com.trolltech.qt.core
Class QSettings

java.lang.Object
  extended by com.trolltech.qt.internal.QSignalEmitterInternal
      extended by com.trolltech.qt.QSignalEmitter
          extended by com.trolltech.qt.QtJambiObject
              extended by com.trolltech.qt.core.QObject
                  extended by com.trolltech.qt.core.QSettings
All Implemented Interfaces:
QtJambiInterface

public class QSettings
extends QObject

The QSettings class provides persistent platform-independent application settings. Users normally expect an application to remember its settings (window sizes and positions, options, etc.) across sessions. This information is often stored in the system registry on Windows, and in XML preferences files on Mac OS X. On Unix systems, in the absence of a standard, many applications (including the KDE applications) use INI text files.

QSettings is an abstraction around these technologies, enabling you to save and restore application settings in a portable manner. It also supports custom storage formats.

QSettings's API is based on QVariant, allowing you to save most value-based types, such as QString, QRect, and QImage, with the minimum of effort.

If all you need is a non-persistent memory-based structure, consider using QMap<QString, QVariant> instead.

Basic Usage

When creating a QSettings object, you must pass the name of your company or organization as well as the name of your application. For example, if your product is called Star Runner and your company is called MySoft, you would construct the QSettings object as follows:
    QSettings settings = new QSettings("MySoft", "Star Runner");
QSettings objects can be created either on the stack or on the heap (i.e. using new). Constructing and destroying a QSettings object is very fast.

If you use QSettings from many places in your application, you might want to specify the organization name and the application name using QCoreApplication::setOrganizationName() and QCoreApplication::setApplicationName(), and then use the default QSettings constructor:

    QCoreApplication.setOrganizationName("MySoft");

    QCoreApplication.setOrganizationDomain("mysoft.com");

    QCoreApplication.setApplicationName("Star Runner");
...
    QSettings settings = new QSettings();
(Here, we also specify the organization's Internet domain. When the Internet domain is set, it is used on Mac OS X instead of the organization name, since Mac OS X applications conventionally use Internet domains to identify themselves. If no domain is set, a fake domain is derived from the organization name. See the Platform-Specific Notes below for details.)

QSettings stores settings. Each setting consists of a QString that specifies the setting's name (the key) and a QVariant that stores the data associated with the key. To write a setting, use setValue(). For example:

    settings.setValue("editor/wrapMargin", 68);
If there already exists a setting with the same key, the existing value is overwritten by the new value. For efficiency, the changes may not be saved to permanent storage immediately. (You can always call sync() to commit your changes.)

You can get a setting's value back using value():

    int margin = (Integer) settings.value("editor/wrapMargin");
If there is no setting with the specified name, QSettings returns a null QVariant (which can be converted to the integer 0). You can specify another default value by passing a second argument to value():
    int margin = (Integer) settings.value("editor/wrapMargin", 80);
To test whether a given key exists, call contains(). To remove the setting associated with a key, call remove(). To obtain the list of all keys, call allKeys(). To remove all keys, call clear().

QVariant and GUI Types

Because
QVariant is part of the QtCore library, it cannot provide conversion functions to data types such as QColor, QImage, and QPixmap, which are part of QtGui. In other words, there is no toColor(), toImage(), or toPixmap() functions in QVariant.

Instead, you can use the QVariant::value() or the qVariantValue() template function. For example:

        QSettings settings = new QSettings("MySoft", "Star Runner");
        QColor color = (QColor) settings.value("DataPump/bgcolor");
The inverse conversion (e.g., from QColor to QVariant) is automatic for all data types supported by QVariant, including GUI-related types:
        QSettings settings = new QSettings("MySoft", "Star Runner");
        QColor color = widget.palette().window().color();
        settings.setValue("DataPump/bgcolor", color);
Custom types registered using qRegisterMetaType() and qRegisterMetaTypeStreamOperators() can be stored using QSettings.

Key Syntax

Setting keys can contain any Unicode characters. The Windows registry and INI files use case-insensitive keys, whereas the Carbon Preferences API on Mac OS X uses case-sensitive keys. To avoid portability problems, follow these two simple rules:
  1. Always refer to the same key using the same case. For example, if you refer to a key as "text fonts" in one place in your code, don't refer to it as "Text Fonts" somewhere else.
  2. Avoid key names that are identical except for the case. For example, if you have a key called "MainWindow", don't try to save another key as "mainwindow".
  3. Do not use slashes ('/' and '\') in key names; the backslash character is used to separate sub keys (see below). On windows '\' are converted by QSettings to '/', which makes them identical.
You can form hierarchical keys using the '/' character as a separator, similar to Unix file paths. For example:
    settings.setValue("mainwindow/size", win.size());

    settings.setValue("mainwindow/fullScreen", win.isFullScreen());

    settings.setValue("outputpanel/visible", panel.isVisible());
If you want to save or restore many settings with the same prefix, you can specify the prefix using beginGroup() and call endGroup() at the end. Here's the same example again, but this time using the group mechanism:
    settings.beginGroup("mainwindow");
    settings.setValue("size", win.size());
    settings.setValue("fullScreen", win.isFullScreen());
    settings.endGroup();

settings.beginGroup("outputpanel"); settings.setValue("visible", panel.isVisible()); settings.endGroup();
If a group is set using beginGroup(), the behavior of most functions changes consequently. Groups can be set recursively.

In addition to groups, QSettings also supports an "array" concept. See beginReadArray() and beginWriteArray() for details.

Fallback Mechanism

Let's assume that you have created a QSettings object with the organization name MySoft and the application name Star Runner. When you look up a value, up to four locations are searched in that order:
  1. a user-specific location for the Star Runner application
  2. a user-specific location for all applications by MySoft
  3. a system-wide location for the Star Runner application
  4. a system-wide location for all applications by MySoft
(See
Platform-Specific Notes below for information on what these locations are on the different platforms supported by Qt.)

If a key cannot be found in the first location, the search goes on in the second location, and so on. This enables you to store system-wide or organization-wide settings and to override them on a per-user or per-application basis. To turn off this mechanism, call setFallbacksEnabled(false).

Although keys from all four locations are available for reading, only the first file (the user-specific location for the application at hand) is accessible for writing. To write to any of the other files, omit the application name and/or specify QSettings::SystemScope (as opposed to QSettings::UserScope , the default).

Let's see with an example:

    QSettings obj1 = new QSettings("MySoft", "Star Runner");

    QSettings obj2 = new QSettings("MySoft");
    QSettings obj3 = new QSettings(QSettings.Scope.SystemScope, "MySoft", "Star Runner");
    QSettings obj4 = new QSettings(QSettings.Scope.SystemScope, "MySoft");
The table below summarizes which QSettings objects access which location. "X" means that the location is the main location associated to the QSettings object and is used both for reading and for writing; "o" means that the location is used as a fallback when reading.
Locations
obj1
obj2
obj3
obj4
1. User, Application X
2. User, Organization o X
3. System, Application o X
4. System, Organization o o o X
The beauty of this mechanism is that it works on all platforms supported by Qt and that it still gives you a lot of flexibility, without requiring you to specify any file names or registry paths.

If you want to use INI files on all platforms instead of the native API, you can pass QSettings::IniFormat as the first argument to the QSettings constructor, followed by the scope, the organization name, and the application name:

    QSettings settings = new QSettings(QSettings.Format.IniFormat,
                                       QSettings.Scope.UserScope,
                                       "MySoft", "Star Runner");
The Settings Editor example lets you experiment with different settings location and with fallbacks turned on or off.

Restoring the State of a GUI Application

QSettings is often used to store the state of a GUI application. The following example illustrates how to use QSettings to save and restore the geometry of an application's main window.
public void writeSettings()
{
    QSettings settings = new QSettings("Moose Soft", "Clipper");

    settings.beginGroup("MainWindow");
    settings.setValue("size", size());
    settings.setValue("pos", pos());
    settings.endGroup();
}

public void readSettings() { QSettings settings = new QSettings("Moose Soft", "Clipper"); settings.beginGroup("MainWindow"); resize((QSize) settings.value("size", new QSize(400, 400))); move((QPoint) settings.value("pos", new QPoint(200, 200))); settings.endGroup(); }
See
Window Geometry for a discussion on why it is better to call QWidget::resize() and QWidget::move() rather than QWidget::setGeometry() to restore a window's geometry.

The readSettings() and writeSettings() functions must be called from the main window's constructor and close event handler as follows:

public MainWindow()
{
...
    readSettings();

}

protected void closeEvent(QCloseEvent event) { if (letsCutItOut()) { writeSettings(); event.accept(); } else { event.ignore(); } }
See the Application example for a self-contained example that uses QSettings.

Accessing Settings from Multiple Threads or Processes Simultaneously

QSettings is
reentrant. This means that you can use distinct QSettings object in different threads simultaneously. This guarantee stands even when the QSettings objects refer to the same files on disk (or to the same entries in the system registry). If a setting is modified through one QSettings object, the change will immediately be visible in any other QSettings objects that operate on the same location and that live in the same process.

QSettings can safely be used from different processes (which can be different instances of your application running at the same time or different applications altogether) to read and write to the same system locations. It uses advisory file locking and a smart merging algorithm to ensure data integrity. Changes performed by another process aren't visible in the current process until sync() is called.

Platform-Specific Notes

Locations Where Application Settings Are Stored

As mentioned in the Fallback Mechanism section, QSettings stores settings for an application in up to four locations, depending on whether the settings are user-specific or system-wide and whether the the settings are application-specific or organization-wide. For simplicity, we're assuming the organization is called MySoft and the application is called Star Runner.

On Unix systems, if the file format is NativeFormat , the following files are used by default:

  1. $HOME/.config/MySoft/Star Runner.conf (Qt for Embedded Linux: $HOME/Settings/MySoft/Star Runner.conf)
  2. $HOME/.config/MySoft.conf (Qt for Embedded Linux: $HOME/Settings/MySoft.conf)
  3. /etc/xdg/MySoft/Star Runner.conf
  4. /etc/xdg/MySoft.conf
On Mac OS X versions 10.2 and 10.3, these files are used by default:
  1. $HOME/Library/Preferences/com.MySoft.Star Runner.plist
  2. $HOME/Library/Preferences/com.MySoft.plist
  3. /Library/Preferences/com.MySoft.Star Runner.plist
  4. /Library/Preferences/com.MySoft.plist
On Windows, NativeFormat settings are stored in the following registry paths:
  1. HKEY_CURRENT_USER\Software\MySoft\Star Runner
  2. HKEY_CURRENT_USER\Software\MySoft
  3. HKEY_LOCAL_MACHINE\Software\MySoft\Star Runner
  4. HKEY_LOCAL_MACHINE\Software\MySoft
If the file format is IniFormat , the following files are used on Unix and Mac OS X:
  1. $HOME/.config/MySoft/Star Runner.ini (Qt for Embedded Linux: $HOME/Settings/MySoft/Star Runner.ini)
  2. $HOME/.config/MySoft.ini (Qt for Embedded Linux: $HOME/Settings/MySoft.ini)
  3. /etc/xdg/MySoft/Star Runner.ini
  4. /etc/xdg/MySoft.ini
On Windows, the following files are used:
  1. %APPDATA%\MySoft\Star Runner.ini
  2. %APPDATA%\MySoft.ini
  3. %COMMON_APPDATA%\MySoft\Star Runner.ini
  4. %COMMON_APPDATA%\MySoft.ini
The %APPDATA% path is usually C:\Documents and Settings\User Name\Application DataUser Name; the %COMMON_APPDATA% path is usually C:\Documents and Settings\All Users\Application Data.

The paths for the .ini and .conf files can be changed using setPath(). On Unix and Mac OS X, the user can override them by by setting the XDG_CONFIG_HOME environment variable; see setPath() for details.

Accessing INI and .plist Files Directly

Sometimes you do want to access settings stored in a specific file or registry path. On all platforms, if you want to read an INI file directly, you can use the QSettings constructor that takes a file name as first argument and pass QSettings::IniFormat as second argument. For example:
        QSettings settings = new QSettings("/home/petra/misc/myapp.ini",
                           QSettings.Format.IniFormat);
You can then use the QSettings object to read and write settings in the file.

On Mac OS X, you can access XML-based .plist files by passing QSettings::NativeFormat as second argument. For example:

        QSettings settings = new QSettings("/Users/petra/misc/myapp.plist",
                           QSettings.Format.NativeFormat);

Accessing the Windows Registry Directly

On Windows, QSettings lets you access settings that have been written with QSettings (or settings in a supported format, e.g., string data) in the system registry. This is done by constructing a QSettings object with a path in the registry and
QSettings::NativeFormat .

For example:

        QSettings settings = new QSettings("HKEY_CURRENT_USER\\Software\\Microsoft\\Office",
                           QSettings.Format.NativeFormat);
All the registry entries that appear under the specified path can be read or written through the QSettings object as usual (using forward slashes instead of backslashes). For example:
        settings.setValue("11.0/Outlook/Security/DontTrustInstalledFiles", 0);
Note that the backslash character is, as mentioned, used by QSettings to separate subkeys. As a result, you cannot read or write windows registry entries that contain slashes or backslashes; you should use a native windows API if you need to do so.

Accessing Common Registry Settings on Windows

On Windows, it is possible for a key to have both a value and subkeys. Its default value is accessed by using "Default" or "." in place of a subkey:
        settings.setValue("HKEY_CURRENT_USER\\MySoft\\Star Runner\\Galaxy", "Milkyway");
        settings.setValue("HKEY_CURRENT_USER\\MySoft\\Star Runner\\Galaxy\\Sun", "OurStar");
        settings.value("HKEY_CURRENT_USER\\MySoft\\Star Runner\\Galaxy\\Default"); // returns "Milkyway"
On other platforms than Windows, "Default" and "." would be treated as regular subkeys.

Platform Limitations

While QSettings attempts to smooth over the differences between the different supported platforms, there are still a few differences that you should be aware of when porting your application:

See also:
QVariant, QSessionManager, Settings Editor Example, and Application Example.


Nested Class Summary
static class QSettings.Format
          This enum type specifies the storage format used by QSettings.
static class QSettings.Scope
          This enum specifies whether settings are user-specific or shared by all users of the same system.
static class QSettings.Status
          The following status values are possible.
 
Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter
QSignalEmitter.AbstractSignal, QSignalEmitter.PrivateSignal0, QSignalEmitter.PrivateSignal1, QSignalEmitter.PrivateSignal2, QSignalEmitter.PrivateSignal3, QSignalEmitter.PrivateSignal4, QSignalEmitter.PrivateSignal5, QSignalEmitter.PrivateSignal6, QSignalEmitter.PrivateSignal7, QSignalEmitter.PrivateSignal8, QSignalEmitter.PrivateSignal9, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9
 
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal
 
Field Summary
 
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
currentSender
 
Constructor Summary
QSettings()
          Constructs a QSettings object for accessing settings of the application and organization set previously with a call to QCoreApplication::setOrganizationName(), QCoreApplication::setOrganizationDomain(), and QCoreApplication::setApplicationName().
QSettings(QObject parent)
          Constructs a QSettings object for accessing settings of the application and organization set previously with a call to QCoreApplication::setOrganizationName(), QCoreApplication::setOrganizationDomain(), and QCoreApplication::setApplicationName().
QSettings(QSettings.Format format, QSettings.Scope scope, java.lang.String organization)
          Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.
QSettings(QSettings.Format format, QSettings.Scope scope, java.lang.String organization, java.lang.String application)
          Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.
QSettings(QSettings.Format format, QSettings.Scope scope, java.lang.String organization, java.lang.String application, QObject parent)
          Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.
QSettings(QSettings.Scope scope, java.lang.String organization)
          Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.
QSettings(QSettings.Scope scope, java.lang.String organization, java.lang.String application)
          Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.
QSettings(QSettings.Scope scope, java.lang.String organization, java.lang.String application, QObject parent)
          Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.
QSettings(java.lang.String organization)
          Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.
QSettings(java.lang.String fileName, QSettings.Format format)
          Constructs a QSettings object for accessing the settings stored in the file called fileName, with parent parent.
QSettings(java.lang.String fileName, QSettings.Format format, QObject parent)
          Constructs a QSettings object for accessing the settings stored in the file called fileName, with parent parent.
QSettings(java.lang.String organization, java.lang.String application)
          Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.
QSettings(java.lang.String organization, java.lang.String application, QObject parent)
          Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.
 
Method Summary
 java.util.List allKeys()
          Returns a list of all keys, including subkeys, that can be read using the QSettings object.
 java.lang.String applicationName()
          Returns the application name used for storing the settings.
 void beginGroup(java.lang.String prefix)
          Appends prefix to the current group.
 int beginReadArray(java.lang.String prefix)
          Adds prefix to the current group and starts reading from an array.
 void beginWriteArray(java.lang.String prefix)
          Adds prefix to the current group and starts writing an array of size size.
 void beginWriteArray(java.lang.String prefix, int size)
          Adds prefix to the current group and starts writing an array of size size.
 java.util.List childGroups()
          Returns a list of all key top-level groups that contain keys that can be read using the QSettings object.
 java.util.List childKeys()
          Returns a list of all top-level keys that can be read using the QSettings object.
 void clear()
          Removes all entries in the primary location associated to this QSettings object.
 boolean contains(java.lang.String key)
          Returns true if there exists a setting called key; returns false otherwise.
static QSettings.Format defaultFormat()
          Returns default file format used for storing settings for the QSettings(QObject *) constructor.
 void endArray()
          Closes the array that was started using beginReadArray() or beginWriteArray().
 void endGroup()
          Resets the group to what it was before the corresponding beginGroup() call.
 boolean fallbacksEnabled()
          Returns true if fallbacks are enabled; returns false otherwise.
 java.lang.String fileName()
          Returns the path where settings written using this QSettings object are stored.
 QSettings.Format format()
          Returns the format used for storing the settings.
 java.lang.String group()
          Returns the current group.
 QTextCodec iniCodec()
          Returns the codec that is used for accessing INI files.
 boolean isWritable()
          Returns true if settings can be written using this QSettings object; returns false otherwise.
 java.lang.String organizationName()
          Returns the organization name used for storing the settings.
 void remove(java.lang.String key)
          Removes the setting key and any sub-settings of key.
 QSettings.Scope scope()
          Returns the scope used for storing the settings.
 void setArrayIndex(int i)
          Sets the current array index to i.
static void setDefaultFormat(QSettings.Format format)
          Sets the default file format to the given format, used for storing settings for the QSettings(QObject *) constructor.
 void setFallbacksEnabled(boolean b)
          Sets whether fallbacks are enabled to b.
 void setIniCodec(QTextCodec codec)
          Sets the codec for accessing INI files (including .
 void setIniCodec(java.lang.String codecName)
          This is an overloaded method provided for convenience.
static void setPath(QSettings.Format format, QSettings.Scope scope, java.lang.String path)
          Sets the path used for storing settings for the given format and scope, to path.
 void setValue(java.lang.String key, java.lang.Object value)
          Sets the value of setting key to value.
 QSettings.Status status()
          Returns a status code indicating the first error that was met by QSettings, or QSettings::NoError if no error occurred.
 void sync()
          Writes any unsaved changes to permanent storage, and reloads any settings that have been changed in the meantime by another application.
 java.lang.Object value(java.lang.String key)
          Returns the value for setting key.
 java.lang.Object value(java.lang.String key, java.lang.Object defaultValue)
          Returns the value for setting key.
 
Methods inherited from class com.trolltech.qt.core.QObject
childEvent, children, connectSlotsByName, customEvent, disposeLater, dumpObjectInfo, dumpObjectTree, dynamicPropertyNames, event, eventFilter, findChild, findChild, findChild, findChildren, findChildren, findChildren, findChildren, indexOfProperty, installEventFilter, isWidgetType, killTimer, moveToThread, objectName, parent, properties, property, removeEventFilter, setObjectName, setParent, setProperty, startTimer, timerEvent, toString, userProperty
 
Methods inherited from class com.trolltech.qt.QtJambiObject
dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
__qt_signalInitialization
 
Methods inherited from class java.lang.Object
clone, getClass, hashCode, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface com.trolltech.qt.QtJambiInterface
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership
 

Constructor Detail

QSettings

public QSettings()
Constructs a QSettings object for accessing settings of the application and organization set previously with a call to QCoreApplication::setOrganizationName(), QCoreApplication::setOrganizationDomain(), and QCoreApplication::setApplicationName().

The scope is QSettings::UserScope and the format is defaultFormat() (QSettings::NativeFormat by default).

The code

        QSettings settings = new QSettings("Moose Soft", "Facturo-Pro");
is equivalent to
        QCoreApplication.setOrganizationName("Moose Soft");
        QCoreApplication.setApplicationName("Facturo-Pro");
        QSettings settings = new QSettings();
If QCoreApplication::setOrganizationName() and QCoreApplication::setApplicationName() has not been previously called, the QSettings object will not be able to read or write any settings, and status() will return AccessError .

On Mac OS X, if both a name and an Internet domain are specified for the organization, the domain is preferred over the name. On other platforms, the name is preferred over the domain.

See also:
QCoreApplication::setOrganizationName(), QCoreApplication::setOrganizationDomain(), QCoreApplication::setApplicationName(), and setDefaultFormat().


QSettings

public QSettings(QObject parent)
Constructs a QSettings object for accessing settings of the application and organization set previously with a call to QCoreApplication::setOrganizationName(), QCoreApplication::setOrganizationDomain(), and QCoreApplication::setApplicationName().

The scope is QSettings::UserScope and the format is defaultFormat() (QSettings::NativeFormat by default).

The code

        QSettings settings = new QSettings("Moose Soft", "Facturo-Pro");
is equivalent to
        QCoreApplication.setOrganizationName("Moose Soft");
        QCoreApplication.setApplicationName("Facturo-Pro");
        QSettings settings = new QSettings();
If QCoreApplication::setOrganizationName() and QCoreApplication::setApplicationName() has not been previously called, the QSettings object will not be able to read or write any settings, and status() will return AccessError .

On Mac OS X, if both a name and an Internet domain are specified for the organization, the domain is preferred over the name. On other platforms, the name is preferred over the domain.

See also:
QCoreApplication::setOrganizationName(), QCoreApplication::setOrganizationDomain(), QCoreApplication::setApplicationName(), and setDefaultFormat().


QSettings

public QSettings(QSettings.Format format,
                 QSettings.Scope scope,
                 java.lang.String organization,
                 java.lang.String application)
Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.

If scope is QSettings::UserScope , the QSettings object searches user-specific settings first, before it searches system-wide settings as a fallback. If scope is QSettings::SystemScope , the QSettings object ignores user-specific settings and provides access to system-wide settings.

If format is QSettings::NativeFormat , the native API is used for storing settings. If format is QSettings::IniFormat , the INI format is used.

If no application name is given, the QSettings object will only access the organization-wide locations.


QSettings

public QSettings(QSettings.Format format,
                 QSettings.Scope scope,
                 java.lang.String organization)
Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.

If scope is QSettings::UserScope , the QSettings object searches user-specific settings first, before it searches system-wide settings as a fallback. If scope is QSettings::SystemScope , the QSettings object ignores user-specific settings and provides access to system-wide settings.

If format is QSettings::NativeFormat , the native API is used for storing settings. If format is QSettings::IniFormat , the INI format is used.

If no application name is given, the QSettings object will only access the organization-wide locations.


QSettings

public QSettings(QSettings.Format format,
                 QSettings.Scope scope,
                 java.lang.String organization,
                 java.lang.String application,
                 QObject parent)
Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.

If scope is QSettings::UserScope , the QSettings object searches user-specific settings first, before it searches system-wide settings as a fallback. If scope is QSettings::SystemScope , the QSettings object ignores user-specific settings and provides access to system-wide settings.

If format is QSettings::NativeFormat , the native API is used for storing settings. If format is QSettings::IniFormat , the INI format is used.

If no application name is given, the QSettings object will only access the organization-wide locations.


QSettings

public QSettings(QSettings.Scope scope,
                 java.lang.String organization,
                 java.lang.String application)
Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.

If scope is QSettings::UserScope , the QSettings object searches user-specific settings first, before it searches system-wide settings as a fallback. If scope is QSettings::SystemScope , the QSettings object ignores user-specific settings and provides access to system-wide settings.

The storage format is QSettings::NativeFormat .

If no application name is given, the QSettings object will only access the organization-wide locations.

See also:
setDefaultFormat().


QSettings

public QSettings(QSettings.Scope scope,
                 java.lang.String organization)
Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.

If scope is QSettings::UserScope , the QSettings object searches user-specific settings first, before it searches system-wide settings as a fallback. If scope is QSettings::SystemScope , the QSettings object ignores user-specific settings and provides access to system-wide settings.

The storage format is QSettings::NativeFormat .

If no application name is given, the QSettings object will only access the organization-wide locations.

See also:
setDefaultFormat().


QSettings

public QSettings(QSettings.Scope scope,
                 java.lang.String organization,
                 java.lang.String application,
                 QObject parent)
Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.

If scope is QSettings::UserScope , the QSettings object searches user-specific settings first, before it searches system-wide settings as a fallback. If scope is QSettings::SystemScope , the QSettings object ignores user-specific settings and provides access to system-wide settings.

The storage format is QSettings::NativeFormat .

If no application name is given, the QSettings object will only access the organization-wide locations.

See also:
setDefaultFormat().


QSettings

public QSettings(java.lang.String fileName,
                 QSettings.Format format)
Constructs a QSettings object for accessing the settings stored in the file called fileName, with parent parent. If the file doesn't already exist, it is created.

If format is QSettings::NativeFormat , the meaning of fileName depends on the platform. On Unix, fileName is the name of an INI file. On Mac OS X, fileName is the name of a .plist file. On Windows, fileName is a path in the system registry.

If format is QSettings::IniFormat , fileName is the name of an INI file.

Warning: This function is provided for convenience. It works well for accessing INI or .plist files generated by Qt, but might fail on some syntaxes found in such files originated by other programs. In particular, be aware of the following limitations:

See also:
fileName().


QSettings

public QSettings(java.lang.String fileName,
                 QSettings.Format format,
                 QObject parent)
Constructs a QSettings object for accessing the settings stored in the file called fileName, with parent parent. If the file doesn't already exist, it is created.

If format is QSettings::NativeFormat , the meaning of fileName depends on the platform. On Unix, fileName is the name of an INI file. On Mac OS X, fileName is the name of a .plist file. On Windows, fileName is a path in the system registry.

If format is QSettings::IniFormat , fileName is the name of an INI file.

Warning: This function is provided for convenience. It works well for accessing INI or .plist files generated by Qt, but might fail on some syntaxes found in such files originated by other programs. In particular, be aware of the following limitations:

See also:
fileName().


QSettings

public QSettings(java.lang.String organization,
                 java.lang.String application)
Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.

Example:

        QSettings settings = new QSettings("Moose Tech", "Facturo-Pro");
The scope is QSettings::UserScope and the format is QSettings::NativeFormat .

See also:
setDefaultFormat(), and Fallback Mechanism.


QSettings

public QSettings(java.lang.String organization)
Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.

Example:

        QSettings settings = new QSettings("Moose Tech", "Facturo-Pro");
The scope is QSettings::UserScope and the format is QSettings::NativeFormat .

See also:
setDefaultFormat(), and Fallback Mechanism.


QSettings

public QSettings(java.lang.String organization,
                 java.lang.String application,
                 QObject parent)
Constructs a QSettings object for accessing settings of the application called application from the organization called organization, and with parent parent.

Example:

        QSettings settings = new QSettings("Moose Tech", "Facturo-Pro");
The scope is QSettings::UserScope and the format is QSettings::NativeFormat .

See also:
setDefaultFormat(), and Fallback Mechanism.

Method Detail

allKeys

public final java.util.List allKeys()
Returns a list of all keys, including subkeys, that can be read using the QSettings object.

Example:

        QSettings settings = new QSettings();
        settings.setValue("fridge/color", Qt.GlobalColor.white);
        settings.setValue("fridge/size", new QSize(32, 96));
        settings.setValue("sofa", true);
        settings.setValue("tv", false);

        List<String> keys = settings.allKeys();
        // keys: ["fridge/color", "fridge/size", "sofa", "tv"]
If a group is set using beginGroup(), only the keys in the group are returned, without the group prefix:
        settings.beginGroup("fridge");
        keys = settings.allKeys();
        // keys: ["color", "size"]

See also:
childGroups(), and childKeys().


applicationName

public final java.lang.String applicationName()
Returns the application name used for storing the settings.

See also:
QCoreApplication::applicationName(), format(), scope(), and organizationName().


beginGroup

public final void beginGroup(java.lang.String prefix)
Appends prefix to the current group.

The current group is automatically prepended to all keys specified to QSettings. In addition, query functions such as childGroups(), childKeys(), and allKeys() are based on the group. By default, no group is set.

Groups are useful to avoid typing in the same setting paths over and over. For example:

        settings.beginGroup("mainwindow");
        settings.setValue("size", win.size());
        settings.setValue("fullScreen", win.isFullScreen());
        settings.endGroup();

        settings.beginGroup("outputpanel");
        settings.setValue("visible", panel.isVisible());
        settings.endGroup();
This will set the value of three settings: Call endGroup() to reset the current group to what it was before the corresponding beginGroup() call. Groups can be nested.

See also:
endGroup(), and group().


beginReadArray

public final int beginReadArray(java.lang.String prefix)
Adds prefix to the current group and starts reading from an array. Returns the size of the array.

Example:

        class Login {
            public String userName;
            public String password;
        };
        List<Login> logins = new ArrayList<Login>();
        // ...

        QSettings settings = new QSettings();
        int size = settings.beginReadArray("logins");
        for (int i = 0; i < size; ++i) {
            settings.setArrayIndex(i);
            Login login = new Login();
            login.userName = settings.value("userName").toString();
            login.password = settings.value("password").toString();
            logins.add(login);
        }
        settings.endArray();
Use beginWriteArray() to write the array in the first place.

See also:
beginWriteArray(), endArray(), and setArrayIndex().


beginWriteArray

public final void beginWriteArray(java.lang.String prefix)
Adds prefix to the current group and starts writing an array of size size. If size is -1 (the default), it is automatically determined based on the indexes of the entries written.

If you have many occurrences of a certain set of keys, you can use arrays to make your life easier. For example, let's suppose that you want to save a variable-length list of user names and passwords. You could then write:

        class Login {
            String userName;
            String password;
        };
        List<Login> logins = new ArrayList<Login>();
        // ...

        QSettings settings = new QSettings();
        settings.beginWriteArray("logins");
        for (int i = 0; i < logins.size(); ++i) {
            settings.setArrayIndex(i);
            settings.setValue("userName", logins.get(i).userName);
            settings.setValue("password", logins.get(i).password);
        }
        settings.endArray();
The generated keys will have the form To read back an array, use beginReadArray().

See also:
beginReadArray(), endArray(), and setArrayIndex().


beginWriteArray

public final void beginWriteArray(java.lang.String prefix,
                                  int size)
Adds prefix to the current group and starts writing an array of size size. If size is -1 (the default), it is automatically determined based on the indexes of the entries written.

If you have many occurrences of a certain set of keys, you can use arrays to make your life easier. For example, let's suppose that you want to save a variable-length list of user names and passwords. You could then write:

        class Login {
            String userName;
            String password;
        };
        List<Login> logins = new ArrayList<Login>();
        // ...

        QSettings settings = new QSettings();
        settings.beginWriteArray("logins");
        for (int i = 0; i < logins.size(); ++i) {
            settings.setArrayIndex(i);
            settings.setValue("userName", logins.get(i).userName);
            settings.setValue("password", logins.get(i).password);
        }
        settings.endArray();
The generated keys will have the form To read back an array, use beginReadArray().

See also:
beginReadArray(), endArray(), and setArrayIndex().


childGroups

public final java.util.List childGroups()
Returns a list of all key top-level groups that contain keys that can be read using the QSettings object.

Example:

        QSettings settings = new QSettings();
        settings.setValue("fridge/color", Qt.GlobalColor.white);
        settings.setValue("fridge/size", new QSize(32, 96));
        settings.setValue("sofa", true);
        settings.setValue("tv", false);

        List<String> groups = settings.childGroups();
        // group: ["fridge"]
If a group is set using beginGroup(), the first-level keys in that group are returned, without the group prefix.
        settings.beginGroup("fridge");
        groups = settings.childGroups();
        // groups: []
You can navigate through the entire setting hierarchy using childKeys() and childGroups() recursively.

See also:
childKeys(), and allKeys().


childKeys

public final java.util.List childKeys()
Returns a list of all top-level keys that can be read using the QSettings object.

Example:

        QSettings settings = new QSettings();
        settings.setValue("fridge/color", Qt.GlobalColor.white);
        settings.setValue("fridge/size", new QSize(32, 96));
        settings.setValue("sofa", true);
        settings.setValue("tv", false);

        List<String> keys = settings.childKeys();
        // keys: ["sofa", "tv"]
If a group is set using beginGroup(), the top-level keys in that group are returned, without the group prefix:
        settings.beginGroup("fridge");
        keys = settings.childKeys();
        // keys: ["color", "size"]
You can navigate through the entire setting hierarchy using childKeys() and childGroups() recursively.

See also:
childGroups(), and allKeys().


clear

public final void clear()
Removes all entries in the primary location associated to this QSettings object.

Entries in fallback locations are not removed.

If you only want to remove the entries in the current group(), use remove("") instead.

See also:
remove(), and setFallbacksEnabled().


contains

public final boolean contains(java.lang.String key)
Returns true if there exists a setting called key; returns false otherwise.

If a group is set using beginGroup(), key is taken to be relative to that group.

Note that the Windows registry and INI files use case-insensitive keys, whereas the Carbon Preferences API on Mac OS X uses case-sensitive keys. To avoid portability problems, see the Key Syntax rules.

See also:
value(), and setValue().


endArray

public final void endArray()
Closes the array that was started using beginReadArray() or beginWriteArray().

See also:
beginReadArray(), and beginWriteArray().


endGroup

public final void endGroup()
Resets the group to what it was before the corresponding beginGroup() call.

Example:

        settings.beginGroup("alpha");
        // settings.group() == "alpha"

        settings.beginGroup("beta");
        // settings.group() == "alpha/beta"

        settings.endGroup();
        // settings.group() == "alpha"

        settings.endGroup();
        // settings.group() == ""

See also:
beginGroup(), and group().


fallbacksEnabled

public final boolean fallbacksEnabled()
Returns true if fallbacks are enabled; returns false otherwise.

By default, fallbacks are enabled.

See also:
setFallbacksEnabled().


fileName

public final java.lang.String fileName()
Returns the path where settings written using this QSettings object are stored.

On Windows, if the format is QSettings::NativeFormat , the return value is a system registry path, not a file path.

See also:
isWritable(), and format().


format

public final QSettings.Format format()
Returns the format used for storing the settings.

See also:
defaultFormat(), fileName(), scope(), organizationName(), and applicationName().


group

public final java.lang.String group()
Returns the current group.

See also:
beginGroup(), and endGroup().


iniCodec

public final QTextCodec iniCodec()
Returns the codec that is used for accessing INI files. By default, no codec is used, so a null pointer is returned.

See also:
setIniCodec().


isWritable

public final boolean isWritable()
Returns true if settings can be written using this QSettings object; returns false otherwise.

One reason why isWritable() might return false is if QSettings operates on a read-only file.

Warning: This function is not perfectly reliable, because the file permissions can change at any time.

See also:
fileName(), status(), and sync().


organizationName

public final java.lang.String organizationName()
Returns the organization name used for storing the settings.

See also:
QCoreApplication::organizationName(), format(), scope(), and applicationName().


remove

public final void remove(java.lang.String key)
Removes the setting key and any sub-settings of key.

Example:

        QSettings settings = new QSettings();
        settings.setValue("ape", 0);
        settings.setValue("monkey", 1);
        settings.setValue("monkey/sea", 2);
        settings.setValue("monkey/doe", 4);

        settings.remove("monkey");
        List<String> keys = settings.allKeys();
        // keys: ["ape"]
Be aware that if one of the fallback locations contains a setting with the same key, that setting will be visible after calling remove().

If key is an empty string, all keys in the current group() are removed. For example:

        QSettings settings = new QSettings();
        settings.setValue("ape", 0);
        settings.setValue("monkey", 1);
        settings.setValue("monkey/sea", 2);
        settings.setValue("monkey/doe", 4);

        settings.beginGroup("monkey");
        settings.remove("");
        settings.endGroup();

        List<String> keys = settings.allKeys();
        // keys: ["ape"]
Note that the Windows registry and INI files use case-insensitive keys, whereas the Carbon Preferences API on Mac OS X uses case-sensitive keys. To avoid portability problems, see the Key Syntax rules.

See also:
setValue(), value(), and contains().


scope

public final QSettings.Scope scope()
Returns the scope used for storing the settings.

See also:
format(), organizationName(), and applicationName().


setArrayIndex

public final void setArrayIndex(int i)
Sets the current array index to i. Calls to functions such as setValue(), value(), remove(), and contains() will operate on the array entry at that index.

You must call beginReadArray() or beginWriteArray() before you can call this function.


setFallbacksEnabled

public final void setFallbacksEnabled(boolean b)
Sets whether fallbacks are enabled to b.

By default, fallbacks are enabled.

See also:
fallbacksEnabled().


setIniCodec

public final void setIniCodec(QTextCodec codec)
Sets the codec for accessing INI files (including . onf files on Unix) to codec. The codec is used for decoding any data that is read from the INI file, and for encoding any data that is written to the file. By default, no codec is used, and non-ASCII characters are encoded using standard INI escape sequences.

Warning: The codec must be set immediately after creating the QSettings object, before accessing any data.

See also:
iniCodec().


setValue

public final void setValue(java.lang.String key,
                           java.lang.Object value)
Sets the value of setting key to value. If the key already exists, the previous value is overwritten.

Note that the Windows registry and INI files use case-insensitive keys, whereas the Carbon Preferences API on Mac OS X uses case-sensitive keys. To avoid portability problems, see the Key Syntax rules.

Example:

        QSettings settings = new QSettings();
        settings.setValue("interval", 30);
        QVariant.toInt(settings.value("interval"));     // returns 30

        settings.setValue("interval", 6.55);
        QVariant.toDouble(settings.value("interval"));  // returns 6.55

See also:
value(), remove(), and contains().


status

public final QSettings.Status status()
Returns a status code indicating the first error that was met by QSettings, or QSettings::NoError if no error occurred.

Be aware that QSettings delays performing some operations. For this reason, you might want to call sync() to ensure that the data stored in QSettings is written to disk before calling status().

See also:
sync().


sync

public final void sync()
Writes any unsaved changes to permanent storage, and reloads any settings that have been changed in the meantime by another application.

This function is called automatically from QSettings's destructor and by the event loop at regular intervals, so you normally don't need to call it yourself.

See also:
status().


value

public final java.lang.Object value(java.lang.String key)
Returns the value for setting key. If the setting doesn't exist, returns defaultValue.

If no default value is specified, a default QVariant is returned.

Note that the Windows registry and INI files use case-insensitive keys, whereas the Carbon Preferences API on Mac OS X uses case-sensitive keys. To avoid portability problems, see the Key Syntax rules.

Example:

        QSettings settings = new QSettings();
        settings.setValue("animal/snake", 58);
        QVariant.toInt(settings.value("animal/snake", 1024));   // returns 58
        QVariant.toInt(settings.value("animal/zebra", 1024));   // returns 1024
        QVariant.toInt(settings.value("animal/zebra"));         // returns 0

See also:
setValue(), contains(), and remove().


value

public final java.lang.Object value(java.lang.String key,
                                    java.lang.Object defaultValue)
Returns the value for setting key. If the setting doesn't exist, returns defaultValue.

If no default value is specified, a default QVariant is returned.

Note that the Windows registry and INI files use case-insensitive keys, whereas the Carbon Preferences API on Mac OS X uses case-sensitive keys. To avoid portability problems, see the Key Syntax rules.

Example:

        QSettings settings = new QSettings();
        settings.setValue("animal/snake", 58);
        QVariant.toInt(settings.value("animal/snake", 1024));   // returns 58
        QVariant.toInt(settings.value("animal/zebra", 1024));   // returns 1024
        QVariant.toInt(settings.value("animal/zebra"));         // returns 0

See also:
setValue(), contains(), and remove().


defaultFormat

public static QSettings.Format defaultFormat()
Returns default file format used for storing settings for the QSettings(QObject *) constructor. If no default format is set, QSettings::NativeFormat is used.

See also:
setDefaultFormat(), and format().


setDefaultFormat

public static void setDefaultFormat(QSettings.Format format)
Sets the default file format to the given format, used for storing settings for the QSettings(QObject *) constructor.

If no default format is set, QSettings::NativeFormat is used.

See also:
defaultFormat(), and format().


setPath

public static void setPath(QSettings.Format format,
                           QSettings.Scope scope,
                           java.lang.String path)
Sets the path used for storing settings for the given format and scope, to path. The format can be a custom format.

The table below summarizes the default values:

Platform
Format
Scope
Path
Windows IniFormat UserScope %APPDATA%
SystemScope %COMMON_APPDATA%
Unix NativeFormat , IniFormat UserScope $HOME/.config
SystemScope /etc/xdg
Qt for Embedded Linux NativeFormat , IniFormat UserScope $HOME/Settings
SystemScope /etc/xdg
Mac OS X IniFormat UserScope $HOME/.config
SystemScope /etc/xdg
The default UserScope paths on Unix and Mac OS X ($HOME/.config or $HOME/Settings) can be overridden by the user by setting the XDG_CONFIG_HOME environment variable. The default SystemScope paths on Unix and Mac OS X (/etc/xdg) can be overridden when building the Qt library using the configure script's --sysconfdir flag (see QLibraryInfo for details).

Setting the NativeFormat paths on Windows and Mac OS X has no effect.

Warning: This function doesn't affect existing QSettings objects.

See also:
registerFormat().


setIniCodec

public final void setIniCodec(java.lang.String codecName)
This is an overloaded method provided for convenience.