com.trolltech.qt.gui
Class QLayout

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.gui.QLayout
All Implemented Interfaces:
QLayoutItemInterface, QtJambiInterface
Direct Known Subclasses:
QBoxLayout, QFormLayout, QGridLayout, QStackedLayout

public abstract class QLayout
extends QObject
implements QLayoutItemInterface

The QLayout class is the base class of geometry managers. This is an abstract base class inherited by the concrete classes QBoxLayout, QGridLayout, QFormLayout, and QStackedLayout.

For users of QLayout subclasses or of QMainWindow there is seldom any need to use the basic functions provided by QLayout, such as setSizeConstraint() or setMenuBar(). See Layout Classes for more information.

To make your own layout manager, implement the functions addItem(), sizeHint(), setGeometry(), itemAt() and takeAt(). You should also implement minimumSize() to ensure your layout isn't resized to zero size if there is too little space. To support children whose heights depend on their widths, implement hasHeightForWidth() and heightForWidth(). See the Border Layout and Flow Layout examples for more information about implementing custom layout managers.

Geometry management stops when the layout manager is deleted.

See also:
QLayoutItem, Layout Classes, Basic Layouts Example, Border Layout Example, and Flow Layout Example.


Nested Class Summary
static class QLayout.SizeConstraint
          The possible values are.
 
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
QLayout()
          Constructs a new child QLayout.
QLayout(QWidget parent)
          Constructs a new top-level QLayout, with parent parent.
 
Method Summary
 boolean activate()
          Redoes the layout for parentWidget() if necessary.
protected  void addChildLayout(QLayout l)
          This function is called from addLayout() or insertLayout() functions in subclasses to add layout l as a sub-layout.
protected  void addChildWidget(QWidget w)
          This function is called from addWidget() functions in subclasses to add w as a child widget.
abstract  void addItem(QLayoutItemInterface arg__1)
          Implemented in subclasses to add an item.
 void addWidget(QWidget w)
          Adds widget w to this layout in a manner specific to the layout.
 Qt.Alignment alignment()
          Returns the alignment of this item.
protected  QRect alignmentRect(QRect arg__1)
          Returns the rectangle that should be covered when the geometry of this layout is set to r, provided that this layout supports setAlignment().
static QSize closestAcceptableSize(QWidget w, QSize s)
          Returns a size that satisfies all size constraints on widget, including heightForWidth() and that is as close as possible to size.
 QRect contentsRect()
          Returns the layout's geometry() rectangle, but taking into account the contents margins.
 QSizePolicy.ControlTypes controlTypes()
          Returns the control type(s) for the layout item.
abstract  int count()
          Must be implemented in subclasses to return the number of items in the layout.
 Qt.Orientations expandingDirections()
          Returns whether this layout item can make use of more space than sizeHint().
 QRect geometry()
          Returns the rectangle covered by this layout item.
 com.trolltech.qt.gui.QContentsMargins getContentsMargins()
          Returns the contents margins of this QLayout.
 boolean hasHeightForWidth()
          Returns true if this layout's preferred height depends on its width; otherwise returns false.
 int heightForWidth(int arg__1)
          Returns the preferred height for this layout item, given the width w.
 int indexOf(QWidget arg__1)
          Searches for widget widget in this layout (not including child layouts).
 void invalidate()
          Invalidates any cached information in this layout item.
 boolean isEmpty()
          Implemented in subclasses to return whether this item is empty, i.e.
 boolean isEnabled()
          Returns true if the layout is enabled; otherwise returns false.
abstract  QLayoutItemInterface itemAt(int index)
          Must be implemented in subclasses to return the layout item at index.
 QLayout layout()
          If this item is a QLayout, it is returned as a QLayout; otherwise 0 is returned.
 QSize maximumSize()
          Implemented in subclasses to return the maximum size of this item.
 QWidget menuBar()
          Returns the menu bar set for this layout, or 0 if no menu bar is set.
 int minimumHeightForWidth(int arg__1)
          Returns the minimum height this widget needs for the given width, w.
 QSize minimumSize()
          Implemented in subclasses to return the minimum size of this item.
 QWidget parentWidget()
          Returns the parent widget of this layout, or 0 if this layout is not installed on any widget.
 void removeItem(QLayoutItemInterface arg__1)
          Removes the layout item item from the layout.
 void removeWidget(QWidget w)
          Removes the widget widget from the layout.
 boolean setAlignment(QLayout l, Qt.Alignment alignment)
          This is an overloaded member function, provided for convenience.
 boolean setAlignment(QLayout l, Qt.AlignmentFlag[] alignment)
          This is an overloaded method provided for convenience.
 void setAlignment(Qt.Alignment alignment)
          Sets the alignment of this item to alignment.
 boolean setAlignment(QWidget w, Qt.Alignment alignment)
          Sets the alignment for widget w to alignment and returns true if w is found in this layout (not including child layouts); otherwise returns false.
 boolean setAlignment(QWidget w, Qt.AlignmentFlag[] alignment)
          This is an overloaded method provided for convenience.
 void setContentsMargins(int left, int top, int right, int bottom)
          Sets the left, top, right, and bottom margins to use around the layout.
 void setContentsMargins(com.trolltech.qt.gui.QContentsMargins margins)
          Sets the contents margins of this QLayout to margins.
 void setEnabled(boolean arg__1)
          Enables this layout if enable is true, otherwise disables it.
 void setGeometry(QRect arg__1)
          Implemented in subclasses to set this item's geometry to r.
 void setMargin(int arg__1)
          This property holds the width of the outside border of the layout.
 void setMenuBar(QWidget w)
          Tells the geometry manager to place the menu bar widget at the top of parentWidget(), outside QWidget::contentsMargins().
 void setSizeConstraint(QLayout.SizeConstraint arg__1)
          This property holds the resize mode of the layout.
 void setWidgetSpacing(int arg__1)
          This property holds the spacing between widgets inside the layout.
 QLayout.SizeConstraint sizeConstraint()
          This property holds the resize mode of the layout.
abstract  QSize sizeHint()
          Implemented in subclasses to return the preferred size of this item.
 QSpacerItem spacerItem()
          If this item is a QSpacerItem, it is returned as a QSpacerItem; otherwise 0 is returned.
abstract  QLayoutItemInterface takeAt(int index)
          Must be implemented in subclasses to remove the layout item at index from the layout, and return the item.
 void update()
          Updates the layout for parentWidget().
 QWidget widget()
          If this item is a QWidget, it is returned as a QWidget; otherwise 0 is returned.
 int widgetSpacing()
          This property holds the spacing between widgets inside the layout.
 
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

QLayout

public QLayout()
Constructs a new child QLayout.

This layout has to be inserted into another layout before geometry management will work.


QLayout

public QLayout(QWidget parent)
Constructs a new top-level QLayout, with parent parent. parent may not be 0.

There can be only one top-level layout for a widget. It is returned by QWidget::layout().

Method Detail

activate

public final boolean activate()
Redoes the layout for parentWidget() if necessary.

You should generally not need to call this because it is automatically called at the most appropriate times. It returns true if the layout was redone.

See also:
update(), and QWidget::updateGeometry().


addChildLayout

protected final void addChildLayout(QLayout l)
This function is called from addLayout() or insertLayout() functions in subclasses to add layout l as a sub-layout.

The only scenario in which you need to call it directly is if you implement a custom layout that supports nested layouts.

See also:
QBoxLayout::addLayout(), QBoxLayout::insertLayout(), and QGridLayout::addLayout().


addChildWidget

protected final void addChildWidget(QWidget w)
This function is called from addWidget() functions in subclasses to add w as a child widget.

If w is already in a layout, this function will give a warning and remove w from the layout. This function must therefore be called before adding w to the layout's data structure.


addWidget

public final void addWidget(QWidget w)
Adds widget w to this layout in a manner specific to the layout. This function uses addItem().


alignment

public final Qt.Alignment alignment()
Returns the alignment of this item.

See also:
setAlignment().

Specified by:
alignment in interface QLayoutItemInterface

alignmentRect

protected final QRect alignmentRect(QRect arg__1)
Returns the rectangle that should be covered when the geometry of this layout is set to r, provided that this layout supports setAlignment().

The result is derived from sizeHint() and expanding(). It is never larger than r.


contentsRect

public final QRect contentsRect()
Returns the layout's geometry() rectangle, but taking into account the contents margins.

See also:
setContentsMargins(), and getContentsMargins().


controlTypes

public final QSizePolicy.ControlTypes controlTypes()
Returns the control type(s) for the layout item. For a QWidgetItem, the control type comes from the widget's size policy; for a QLayoutItem, the control types is derived from the layout's contents.

See also:
QSizePolicy::controlType().

Specified by:
controlTypes in interface QLayoutItemInterface

isEnabled

public final boolean isEnabled()
Returns true if the layout is enabled; otherwise returns false.

See also:
setEnabled().


menuBar

public final QWidget menuBar()
Returns the menu bar set for this layout, or 0 if no menu bar is set.

See also:
setMenuBar().


parentWidget

public final QWidget parentWidget()
Returns the parent widget of this layout, or 0 if this layout is not installed on any widget.

If the layout is a sub-layout, this function returns the parent widget of the parent layout.

See also:
parent().


removeItem

public final void removeItem(QLayoutItemInterface arg__1)
Removes the layout item item from the layout. It is the caller's responsibility to delete the item.

Notice that item can be a layout (since QLayout inherits QLayoutItem).

See also:
removeWidget(), and addItem().


removeWidget

public final void removeWidget(QWidget w)
Removes the widget widget from the layout. After this call, it is the caller's responsibility to give the widget a reasonable geometry or to put the widget back into a layout.

Note: The ownership of widget remains the same as when it was added.

See also:
removeItem(), QWidget::setGeometry(), and addWidget().


setAlignment

public final void setAlignment(Qt.Alignment alignment)
Sets the alignment of this item to alignment.

Note: Item alignment is only supported by QLayoutItem subclasses where it would have a visual effect. Except for QSpacerItem, which provides blank space for layouts, all public Qt classes that inherit QLayoutItem support item alignment.

See also:
alignment().

Specified by:
setAlignment in interface QLayoutItemInterface

setAlignment

public final boolean setAlignment(QLayout l,
                                  Qt.AlignmentFlag[] alignment)
This is an overloaded method provided for convenience.


setAlignment

public final boolean setAlignment(QLayout l,
                                  Qt.Alignment alignment)
This is an overloaded member function, provided for convenience.

Sets the alignment for the layout l to alignment and returns true if l is found in this layout (not including child layouts); otherwise returns false.


setAlignment

public final boolean setAlignment(QWidget w,
                                  Qt.AlignmentFlag[] alignment)
This is an overloaded method provided for convenience.


setAlignment

public final boolean setAlignment(QWidget w,
                                  Qt.Alignment alignment)
Sets the alignment for widget w to alignment and returns true if w is found in this layout (not including child layouts); otherwise returns false.


setContentsMargins

public final void setContentsMargins(int left,
                                     int top,
                                     int right,
                                     int bottom)
Sets the left, top, right, and bottom margins to use around the layout.

By default, QLayout uses the values provided by the style. On most platforms, the margin is 11 pixels in all directions.

See also:
getContentsMargins(), QStyle::pixelMetric(), PM_LayoutLeftMargin , PM_LayoutTopMargin , PM_LayoutRightMargin , and PM_LayoutBottomMargin .


setEnabled

public final void setEnabled(boolean arg__1)
Enables this layout if enable is true, otherwise disables it.

An enabled layout adjusts dynamically to changes; a disabled layout acts as if it did not exist.

By default all layouts are enabled.

See also:
isEnabled().


setMargin

public final void setMargin(int arg__1)
This property holds the width of the outside border of the layout. Use setContentsMargins() and getContentsMargins() instead.

See also:
contentsRect(), and spacing.


setMenuBar

public final void setMenuBar(QWidget w)
Tells the geometry manager to place the menu bar widget at the top of parentWidget(), outside QWidget::contentsMargins(). All child widgets are placed below the bottom edge of the menu bar.

See also:
menuBar().


setSizeConstraint

public final void setSizeConstraint(QLayout.SizeConstraint arg__1)
This property holds the resize mode of the layout. The default mode is SetDefaultConstraint .


setWidgetSpacing

public final void setWidgetSpacing(int arg__1)
This property holds the spacing between widgets inside the layout. If no value is explicitly set, the layout's spacing is inherited from the parent layout, or from the style settings for the parent widget.

For QGridLayout and QFormLayout, it is possible to set different horizontal and vertical spacings using setHorizontalSpacing() and setVerticalSpacing(). In that case, spacing() returns -1.

See also:
contentsRect(), getContentsMargins(), QStyle::layoutSpacing(), and QStyle::pixelMetric().


sizeConstraint

public final QLayout.SizeConstraint sizeConstraint()
This property holds the resize mode of the layout. The default mode is SetDefaultConstraint .


widgetSpacing

public final int widgetSpacing()
This property holds the spacing between widgets inside the layout. If no value is explicitly set, the layout's spacing is inherited from the parent layout, or from the style settings for the parent widget.

For QGridLayout and QFormLayout, it is possible to set different horizontal and vertical spacings using setHorizontalSpacing() and setVerticalSpacing(). In that case, spacing() returns -1.

See also:
contentsRect(), getContentsMargins(), QStyle::layoutSpacing(), and QStyle::pixelMetric().


update

public final void update()
Updates the layout for parentWidget().

You should generally not need to call this because it is automatically called at the most appropriate times.

See also:
activate(), and invalidate().


addItem

public abstract void addItem(QLayoutItemInterface arg__1)
Implemented in subclasses to add an item. How it is added is specific to each subclass.

This function is not usually called in application code. To add a widget to a layout, use the addWidget() function; to add a child layout, use the addLayout() function provided by the relevant QLayout subclass.

Note: The ownership of item is transferred to the layout, and it's the layout's responsibility to delete it.

See also:
addWidget(), QBoxLayout::addLayout(), and QGridLayout::addLayout().


count

public abstract int count()
Must be implemented in subclasses to return the number of items in the layout.

See also:
itemAt().


expandingDirections

public Qt.Orientations expandingDirections()
Returns whether this layout item can make use of more space than sizeHint(). A value of Qt::Vertical or Qt::Horizontal means that it wants to grow in only one dimension, whereas Qt::Vertical | Qt::Horizontal means that it wants to grow in both dimensions.

Specified by:
expandingDirections in interface QLayoutItemInterface

geometry

public QRect geometry()
Returns the rectangle covered by this layout item.

See also:
setGeometry().

Specified by:
geometry in interface QLayoutItemInterface

hasHeightForWidth

public boolean hasHeightForWidth()
Returns true if this layout's preferred height depends on its width; otherwise returns false. The default implementation returns false.

Reimplement this function in layout managers that support height for width.

See also:
heightForWidth(), and QWidget::heightForWidth().

Specified by:
hasHeightForWidth in interface QLayoutItemInterface

heightForWidth

public int heightForWidth(int arg__1)
Returns the preferred height for this layout item, given the width w.

The default implementation returns -1, indicating that the preferred height is independent of the width of the item. Using the function hasHeightForWidth() will typically be much faster than calling this function and testing for -1.

Reimplement this function in layout managers that support height for width. A typical implementation will look like this:

    public int heightForWidth(int w)
    {
        if (cache_dirty || cached_width != w) {
            int h = calculateHeightForWidth(w);
            cached_hfw = h;
            return h;
        }
        return cached_hfw;
    }
Caching is strongly recommended; without it layout will take exponential time.

See also:
hasHeightForWidth().

Specified by:
heightForWidth in interface QLayoutItemInterface

indexOf

public int indexOf(QWidget arg__1)
Searches for widget widget in this layout (not including child layouts).

Returns the index of widget, or -1 if widget is not found.

The default implementation iterates over all items using itemAt()


invalidate

public void invalidate()
Invalidates any cached information in this layout item.

Specified by:
invalidate in interface QLayoutItemInterface

isEmpty

public boolean isEmpty()
Implemented in subclasses to return whether this item is empty, i.e. whether it contains any widgets.

Specified by:
isEmpty in interface QLayoutItemInterface

itemAt

public abstract QLayoutItemInterface itemAt(int index)
Must be implemented in subclasses to return the layout item at index. If there is no such item, the function must return 0. Items are numbered consecutively from 0. If an item is deleted, other items will be renumbered.

This function can be used to iterate over a layout. The following code will draw a rectangle for each layout item in the layout structure of the widget.

        static void paintLayout(QPainter painter, QLayoutItemInterface item)
        {
            QLayout layout = item.layout();
            if (layout!=null) {
                for (int i = 0; i < layout.count(); ++i)
                    paintLayout(painter, layout.itemAt(i));
            }
            painter.drawRect(layout.geometry());
        }

        protected void paintEvent(QPaintEvent event)
        {
            QPainter painter = new QPainter(this);
            if (layout() != null)
                paintLayout(painter, layout());
        }

See also:
count(), and takeAt().


layout

public QLayout layout()
If this item is a QLayout, it is returned as a QLayout; otherwise 0 is returned. This function provides type-safe casting.

Specified by:
layout in interface QLayoutItemInterface

maximumSize

public QSize maximumSize()
Implemented in subclasses to return the maximum size of this item.

Specified by:
maximumSize in interface QLayoutItemInterface

minimumHeightForWidth

public int minimumHeightForWidth(int arg__1)
Returns the minimum height this widget needs for the given width, w. The default implementation simply returns heightForWidth(w).

Specified by:
minimumHeightForWidth in interface QLayoutItemInterface

minimumSize

public QSize minimumSize()
Implemented in subclasses to return the minimum size of this item.

Specified by:
minimumSize in interface QLayoutItemInterface

setGeometry

public void setGeometry(QRect arg__1)
Implemented in subclasses to set this item's geometry to r.

See also:
geometry().

Specified by:
setGeometry in interface QLayoutItemInterface

sizeHint

public abstract QSize sizeHint()
Implemented in subclasses to return the preferred size of this item.

Specified by:
sizeHint in interface QLayoutItemInterface

spacerItem

public QSpacerItem spacerItem()
If this item is a QSpacerItem, it is returned as a QSpacerItem; otherwise 0 is returned. This function provides type-safe casting.

Specified by:
spacerItem in interface QLayoutItemInterface

takeAt

public abstract QLayoutItemInterface takeAt(int index)
Must be implemented in subclasses to remove the layout item at index from the layout, and return the item. If there is no such item, the function must do nothing and return 0. Items are numbered consecutively from 0. If an item is deleted, other items will be renumbered.

The following code fragment shows a safe way to remove all items from a layout:

        QLayoutItemInterface child = null;
        while ((child = layout.takeAt(0)) != null) {
            //...
            //delete child;
        }

See also:
itemAt(), and count().


widget

public QWidget widget()
If this item is a QWidget, it is returned as a QWidget; otherwise 0 is returned. This function provides type-safe casting.

Specified by:
widget in interface QLayoutItemInterface

closestAcceptableSize

public static QSize closestAcceptableSize(QWidget w,
                                          QSize s)
Returns a size that satisfies all size constraints on widget, including heightForWidth() and that is as close as possible to size.


getContentsMargins

public final com.trolltech.qt.gui.QContentsMargins getContentsMargins()
Returns the contents margins of this QLayout.


setContentsMargins

public final void setContentsMargins(com.trolltech.qt.gui.QContentsMargins margins)
Sets the contents margins of this QLayout to margins.