com.trolltech.qt.core
Class QIODevice

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.QIODevice
All Implemented Interfaces:
QtJambiInterface
Direct Known Subclasses:
QAbstractSocket, QBuffer, QFile, QLocalSocket, QNetworkReply, QProcess

public abstract class QIODevice
extends QObject

The QIODevice class is the base interface class of all I/O devices in Qt. QIODevice provides both a common implementation and an abstract interface for devices that support reading and writing of blocks of data, such as QFile, QBuffer and QTcpSocket. QIODevice is abstract and can not be instantiated, but it is common to use the interface it defines to provide device-independent I/O features. For example, Qt's XML classes operate on a QIODevice pointer, allowing them to be used with various devices (such as files and buffers).

Before accessing the device, open() must be called to set the correct OpenMode (such as ReadOnly or ReadWrite ). You can then write to the device with write() or putChar(), and read by calling either read(), readLine(), or readAll(). Call close() when you are done with the device.

QIODevice distinguishes between two types of devices: random-access devices and sequential devices.

You can use isSequential() to determine the type of device.

QIODevice emits readyRead() when new data is available for reading; for example, if new data has arrived on the network or if additional data is appended to a file that you are reading from. You can call bytesAvailable() to determine the number of bytes that currently available for reading. It's common to use bytesAvailable() together with the readyRead() signal when programming with asynchronous devices such as QTcpSocket, where fragments of data can arrive at arbitrary points in time. QIODevice emits the bytesWritten() signal every time a payload of data has been written to the device. Use bytesToWrite() to determine the current amount of data waiting to be written.

Certain subclasses of QIODevice, such as QTcpSocket and QProcess, are asynchronous. This means that I/O functions such as write() or read() always return immediately, while communication with the device itself may happen when control goes back to the event loop. QIODevice provides functions that allow you to force these operations to be performed immediately, while blocking the calling thread and without entering the event loop. This allows QIODevice subclasses to be used without an event loop, or in a separate thread:

Calling these functions from the main, GUI thread, may cause your user interface to freeze. Example:
        QProcess gzip = new QProcess();
        gzip.start("gzip", Arrays.asList("-c"));
        if (!gzip.waitForStarted())
            return false;

        gzip.write(new QByteArray("uncompressed data"));

        QByteArray compressed = new QByteArray();
        while (gzip.waitForReadyRead(5000))
            compressed.append(gzip.readAll());
By subclassing QIODevice, you can provide the same interface to your own I/O devices. Subclasses of QIODevice are only required to implement the protected readData() and writeData() functions. QIODevice uses these functions to implement all its convenience functions, such as getChar(), readLine() and write(). QIODevice also handles access control for you, so you can safely assume that the device is opened in write mode if writeData() is called.

Some subclasses, such as QFile and QTcpSocket, are implemented using a memory buffer for intermediate storing of data. This reduces the number of required device accessing calls, which are often very slow. Buffering makes functions like getChar() and putChar() fast, as they can operate on the memory buffer instead of directly on the device itself. Certain I/O operations, however, don't work well with a buffer. For example, if several users open the same device and read it character by character, they may end up reading the same data when they meant to read a separate chunk each. For this reason, QIODevice allows you to bypass any buffering by passing the Unbuffered flag to open(). When subclassing QIODevice, remember to bypass any buffer you may use when the device is open in Unbuffered mode.

See also:
QBuffer, QFile, and QTcpSocket.


Nested Class Summary
static class QIODevice.OpenMode
           
static class QIODevice.OpenModeFlag
          This enum is used with open() to describe the mode in which a device is opened.
 
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
 QSignalEmitter.Signal0 aboutToClose
          This signal is emitted when the device is about to close.
 QSignalEmitter.Signal1 bytesWritten
          This signal takes 1 generic argument(s).
 QSignalEmitter.Signal0 readChannelFinished
          This signal is emitted when the input (reading) stream is closed in this device.
 QSignalEmitter.Signal0 readyRead
          This signal is emitted once every time new data is available for reading from the device.
 
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
currentSender
 
Constructor Summary
QIODevice()
          Constructs a QIODevice object.
QIODevice(QObject parent)
          Constructs a QIODevice object with the given parent.
 
Method Summary
 boolean atEnd()
          Returns true if the current read and write position is at the end of the device (i.
 long bytesAvailable()
          Returns the number of bytes that are available for reading.
 long bytesToWrite()
          For buffered devices, this function returns the number of bytes waiting to be written.
 boolean canReadLine()
          Returns true if a complete line of data can be read from the device; otherwise returns false.
 void close()
          First emits aboutToClose() , then closes the device and sets its OpenMode to NotOpen .
 java.lang.String errorString()
          Returns a human-readable description of the last device error that occurred.
 int getByte()
          Gets a byte from the device.
 boolean isOpen()
          Returns true if the device is open; otherwise returns false.
 boolean isReadable()
          Returns true if data can be read from the device; otherwise returns false.
 boolean isSequential()
          Returns true if this device is sequential; otherwise returns false.
 boolean isTextModeEnabled()
          Returns true if the Text flag is enabled; otherwise returns false.
 boolean isWritable()
          Returns true if data can be written to the device; otherwise returns false.
 boolean open(QIODevice.OpenMode mode)
          Opens the device and sets its OpenMode to mode.
 boolean open(QIODevice.OpenModeFlag[] mode)
           
 QIODevice.OpenMode openMode()
          Returns the mode in which the device has been opened; i.
 int peek(byte[] data)
           
 QByteArray peek(long maxlen)
          This is an overloaded member function, provided for convenience.
 long pos()
          For random-access devices, this function returns the position that data is written to or read from.
 boolean putByte(byte c)
          Writes the character c to the device.
 int read(byte[] data)
           
 QByteArray read(long maxlen)
          This is an overloaded member function, provided for convenience.
 QByteArray readAll()
          This is an overloaded member function, provided for convenience.
protected abstract  int readData(byte[] data)
          Reads up to maxSize bytes from the device into data, and returns the number of bytes read or -1 if an error occurred.
 QByteArray readLine()
          This is an overloaded member function, provided for convenience.
 int readLine(byte[] data)
           
 QByteArray readLine(long maxlen)
          This is an overloaded member function, provided for convenience.
protected  int readLineData(byte[] data)
          Reads up to maxSize characters into data and returns the number of characters read.
 boolean reset()
          Seeks to the start of input for random-access devices.
 boolean seek(long pos)
          For random-access devices, this function sets the current position to pos, returning true on success, or false if an error occurred.
protected  void setErrorString(java.lang.String errorString)
          Sets the human readable description of the last device error that occurred to str.
protected  void setOpenMode(QIODevice.OpenMode openMode)
          Sets the OpenMode of the device to openMode.
protected  void setOpenMode(QIODevice.OpenModeFlag[] openMode)
           
 void setTextModeEnabled(boolean enabled)
          If enabled is true, this function sets the Text flag on the device; otherwise the Text flag is removed.
 long size()
          For open random-access devices, this function returns the size of the device.
 void ungetByte(byte c)
          Puts the character c back into the device, and decrements the current position unless the position is 0.
 boolean waitForBytesWritten(int msecs)
          For buffered devices, this function waits until a payload of buffered written data has been written to the device and the bytesWritten() signal has been emitted, or until msecs milliseconds have passed.
 boolean waitForReadyRead(int msecs)
          Blocks until data is available for reading and the readyRead() signal has been emitted, or until msecs milliseconds have passed.
 int write(byte[] data)
           
 long write(QByteArray data)
          This is an overloaded member function, provided for convenience.
protected abstract  int writeData(byte[] data)
          Writes up to maxSize bytes from data to the device.
 
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
 

Field Detail

aboutToClose

public final QSignalEmitter.Signal0 aboutToClose
This signal is emitted when the device is about to close. Connect this signal if you have operations that need to be performed before the device closes (e.g., if you have data in a separate buffer that needs to be written to the device).


bytesWritten

public final QSignalEmitter.Signal1 bytesWritten

This signal takes 1 generic argument(s). We list their type and the name they go by in the description of this signal. <java.lang.Long(named: bytes)>:

This signal is emitted every time a payload of data has been written to the device. The bytes argument is set to the number of bytes that were written in this payload.

bytesWritten() is not emitted recursively; if you reenter the event loop or call waitForBytesWritten() inside a slot connected to the bytesWritten() signal, the signal will not be reemitted (although waitForBytesWritten() may still return true).

See also:
readyRead() .


readChannelFinished

public final QSignalEmitter.Signal0 readChannelFinished
This signal is emitted when the input (reading) stream is closed in this device. It is emitted as soon as the closing is detected, which means that there might still be data available for reading with read().

See also:
atEnd(), and read().


readyRead

public final QSignalEmitter.Signal0 readyRead
This signal is emitted once every time new data is available for reading from the device. It will only be emitted again once new data is available, such as when a new payload of network data has arrived on your network socket, or when a new block of data has been appended to your device.

readyRead() is not emitted recursively; if you reenter the event loop or call waitForReadyRead() inside a slot connected to the readyRead() signal, the signal will not be reemitted (although waitForReadyRead() may still return true).

Note for developers implementing classes derived from QIODevice: you should always emit readyRead() when new data has arrived (do not emit it only because there's data still to be read in your buffers). Do not emit readyRead() in other conditions.

See also:
bytesWritten() .

Constructor Detail

QIODevice

public QIODevice()
Constructs a QIODevice object.


QIODevice

public QIODevice(QObject parent)
Constructs a QIODevice object with the given parent.

Method Detail

errorString

public final java.lang.String errorString()
Returns a human-readable description of the last device error that occurred.

See also:
setErrorString().


isOpen

public final boolean isOpen()
Returns true if the device is open; otherwise returns false. A device is open if it can be read from and/or written to. By default, this function returns false if openMode() returns NotOpen.

See also:
openMode(), and OpenMode.


isReadable

public final boolean isReadable()
Returns true if data can be read from the device; otherwise returns false. Use bytesAvailable() to determine how many bytes can be read.

This is a convenience function which checks if the OpenMode of the device contains the ReadOnly flag.

See also:
openMode(), and OpenMode.


isTextModeEnabled

public final boolean isTextModeEnabled()
Returns true if the Text flag is enabled; otherwise returns false.

See also:
setTextModeEnabled().


isWritable

public final boolean isWritable()
Returns true if data can be written to the device; otherwise returns false.

This is a convenience function which checks if the OpenMode of the device contains the WriteOnly flag.

See also:
openMode(), and OpenMode.


openMode

public final QIODevice.OpenMode openMode()
Returns the mode in which the device has been opened; i. . ReadOnly or WriteOnly .

See also:
setOpenMode(), and OpenMode.


peek

public final QByteArray peek(long maxlen)
This is an overloaded member function, provided for convenience.

Peeks at most maxSize bytes from the device, returning the data peeked as a QByteArray.

Example:

        public boolean isExeFile(QFile file)
        {
            return file.peek(2).equals("MZ");
        }
This function has no way of reporting errors; returning an empty QByteArray() can mean either that no data was currently available for peeking, or that an error occurred.

See also:
read().


putByte

public final boolean putByte(byte c)
Writes the character c to the device. Returns true on success; otherwise returns false.

See also:
write(), getChar(), and ungetChar().


read

public final QByteArray read(long maxlen)
This is an overloaded member function, provided for convenience.

Reads at most maxSize bytes from the device, and returns the data read as a QByteArray.

This function has no way of reporting errors; returning an empty QByteArray() can mean either that no data was currently available for reading, or that an error occurred.


readAll

public final QByteArray readAll()
This is an overloaded member function, provided for convenience.

Reads all available data from the device, and returns it as a QByteArray.

This function has no way of reporting errors; returning an empty QByteArray() can mean either that no data was currently available for reading, or that an error occurred.


readLine

public final QByteArray readLine()
This is an overloaded member function, provided for convenience.

Reads a line from the device, but no more than maxSize characters, and returns the result as a QByteArray.

This function has no way of reporting errors; returning an empty QByteArray() can mean either that no data was currently available for reading, or that an error occurred.


readLine

public final QByteArray readLine(long maxlen)
This is an overloaded member function, provided for convenience.

Reads a line from the device, but no more than maxSize characters, and returns the result as a QByteArray.

This function has no way of reporting errors; returning an empty QByteArray() can mean either that no data was currently available for reading, or that an error occurred.


setErrorString

protected final void setErrorString(java.lang.String errorString)
Sets the human readable description of the last device error that occurred to str.

See also:
errorString().


setOpenMode

protected final void setOpenMode(QIODevice.OpenModeFlag[] openMode)

setOpenMode

protected final void setOpenMode(QIODevice.OpenMode openMode)
Sets the OpenMode of the device to openMode. Call this function to set the open mode if the flags change after the device has been opened.

See also:
openMode(), and OpenMode.


setTextModeEnabled

public final void setTextModeEnabled(boolean enabled)
If enabled is true, this function sets the Text flag on the device; otherwise the Text flag is removed. This feature is useful for classes that provide custom end-of-line handling on a QIODevice.

See also:
isTextModeEnabled(), open(), and setOpenMode().


ungetByte

public final void ungetByte(byte c)
Puts the character c back into the device, and decrements the current position unless the position is 0. This function is usually called to "undo" a getChar() operation, such as when writing a backtracking parser.

If c was not previously read from the device, the behavior is undefined.


write

public final long write(QByteArray data)
This is an overloaded member function, provided for convenience.

Writes the content of byteArray to the device. Returns the number of bytes that were actually written, or -1 if an error occurred.

See also:
read(), and writeData().


atEnd

public boolean atEnd()
Returns true if the current read and write position is at the end of the device (i. . there is no more data available for reading on the device); otherwise returns false.

For some devices, atEnd() can return true even though there is more data to read. This special case only applies to devices that generate data in direct response to you calling read() (e.g., /dev or /proc files on Unix and Mac OS X, or console input / stdin on all platforms).

See also:
bytesAvailable(), read(), and isSequential().


bytesAvailable

public long bytesAvailable()
Returns the number of bytes that are available for reading. This function is commonly used with sequential devices to determine the number of bytes to allocate in a buffer before reading.

Subclasses that reimplement this function must call the base implementation in order to include the size of QIODevices' buffer. Example:

        public long bytesAvailable()
        {
            return buffer.size() + super.bytesAvailable();
        }

See also:
bytesToWrite(), readyRead() , and isSequential().


bytesToWrite

public long bytesToWrite()
For buffered devices, this function returns the number of bytes waiting to be written. For devices with no buffer, this function returns 0.

See also:
bytesAvailable(), bytesWritten() , and isSequential().


canReadLine

public boolean canReadLine()
Returns true if a complete line of data can be read from the device; otherwise returns false.

Note that unbuffered devices, which have no way of determining what can be read, always return false.

This function is often called in conjunction with the readyRead() signal.

Subclasses that reimplement this function must call the base implementation in order to include the size of the QIODevice's buffer. Example:

        public boolean canReadLine()
        {
            return buffer.contains("\n") || super.canReadLine();
        }

See also:
readyRead() , and readLine().


close

public void close()
First emits aboutToClose() , then closes the device and sets its OpenMode to NotOpen . The error string is also reset.

See also:
setOpenMode(), and OpenMode.


isSequential

public boolean isSequential()
Returns true if this device is sequential; otherwise returns false.

Sequential devices, as opposed to a random-access devices, have no concept of a start, an end, a size, or a current position, and they do not support seeking. You can only read from the device when it reports that data is available. The most common example of a sequential device is a network socket. On Unix, special files such as /dev/zero and fifo pipes are sequential.

Regular files, on the other hand, do support random access. They have both a size and a current position, and they also support seeking backwards and forwards in the data stream. Regular files are non-sequential.

See also:
bytesAvailable().


open

public final boolean open(QIODevice.OpenModeFlag[] mode)

open

public boolean open(QIODevice.OpenMode mode)
Opens the device and sets its OpenMode to mode. Returns true if successful; otherwise returns false. This function should be called from any reimplementations of open() or other functions that open the device.

See also:
openMode(), and OpenMode.


pos

public long pos()
For random-access devices, this function returns the position that data is written to or read from. For sequential devices or closed devices, where there is no concept of a "current position", 0 is returned.

The current read/write position of the device is maintained internally by QIODevice, so reimplementing this function is not necessary. When subclassing QIODevice, use QIODevice::seek() to notify QIODevice about changes in the device position.

See also:
isSequential(), and seek().


readData

protected abstract int readData(byte[] data)
Reads up to maxSize bytes from the device into data, and returns the number of bytes read or -1 if an error occurred. If there are no bytes to be read, this function should return -1 if there can never be more bytes available (for example: socket closed, pipe closed, sub-process finished).

This function is called by QIODevice. Reimplement this function when creating a subclass of QIODevice.

See also:
read(), readLine(), and writeData().


readLineData

protected int readLineData(byte[] data)
Reads up to maxSize characters into data and returns the number of characters read.

This function is called by readLine(), and provides its base implementation, using getChar(). Buffered devices can improve the performance of readLine() by reimplementing this function.

readLine() appends a '\0' byte to data; readLineData() does not need to do this.

If you reimplement this function, be careful to return the correct value: it should return the number of bytes read in this line, including the terminating newline, or 0 if there is no line to be read at this point. If an error occurs, it should return -1 if and only if no bytes were read. Reading past EOF is considered an error.


reset

public boolean reset()
Seeks to the start of input for random-access devices. Returns true on success; otherwise returns false (for example, if the device is not open).

Note that when using a QTextStream on a QFile, calling reset() on the QFile will not have the expected result because QTextStream buffers the file. Use the QTextStream::seek() function instead.

See also:
seek().


seek

public boolean seek(long pos)
For random-access devices, this function sets the current position to pos, returning true on success, or false if an error occurred. For sequential devices, the default behavior is to do nothing and return false.

When subclassing QIODevice, you must call QIODevice::seek() at the start of your function to ensure integrity with QIODevice's built-in buffer. The base implementation always returns true.

See also:
pos(), and isSequential().


size

public long size()
For open random-access devices, this function returns the size of the device. For open sequential devices, bytesAvailable() is returned.

If the device is closed, the size returned will not reflect the actual size of the device.

See also:
isSequential(), and pos().


waitForBytesWritten

public boolean waitForBytesWritten(int msecs)
For buffered devices, this function waits until a payload of buffered written data has been written to the device and the bytesWritten() signal has been emitted, or until msecs milliseconds have passed. If msecs is -1, this function will not time out. For unbuffered devices, it returns immediately.

Returns true if a payload of data was written to the device; otherwise returns false (i.e. if the operation timed out, or if an error occurred).

This function can operate without an event loop. It is useful when writing non-GUI applications and when performing I/O operations in a non-GUI thread.

If called from within a slot connected to the bytesWritten() signal, bytesWritten() will not be reemitted.

Reimplement this function to provide a blocking API for a custom device. The default implementation does nothing, and returns false.

Warning: Calling this function from the main (GUI) thread might cause your user interface to freeze.

See also:
waitForReadyRead().


waitForReadyRead

public boolean waitForReadyRead(int msecs)
Blocks until data is available for reading and the readyRead() signal has been emitted, or until msecs milliseconds have passed. If msecs is -1, this function will not time out.

Returns true if data is available for reading; otherwise returns false (if the operation timed out or if an error occurred).

This function can operate without an event loop. It is useful when writing non-GUI applications and when performing I/O operations in a non-GUI thread.

If called from within a slot connected to the readyRead() signal, readyRead() will not be reemitted.

Reimplement this function to provide a blocking API for a custom device. The default implementation does nothing, and returns false.

Warning: Calling this function from the main (GUI) thread might cause your user interface to freeze.

See also:
waitForBytesWritten().


writeData

protected abstract int writeData(byte[] data)
Writes up to maxSize bytes from data to the device. Returns the number of bytes written, or -1 if an error occurred.

This function is called by QIODevice. Reimplement this function when creating a subclass of QIODevice.

See also:
read(), and write().


getByte

public final int getByte()
Gets a byte from the device.

Returns:
-1 on failure, or the value of the byte on success

peek

public final int peek(byte[] data)

read

public final int read(byte[] data)

readLine

public final int readLine(byte[] data)

write

public final int write(byte[] data)