com.trolltech.qt.gui
Class QGraphicsLayout

java.lang.Object
  com.trolltech.qt.internal.QSignalEmitterInternal
      com.trolltech.qt.QSignalEmitter
          com.trolltech.qt.QtJambiObject
              com.trolltech.qt.gui.QGraphicsLayout

All Implemented Interfaces:

QGraphicsLayoutItemInterface, QtJambiInterface

Direct Known Subclasses:

QGraphicsGridLayout, QGraphicsLinearLayout

public abstract class QGraphicsLayout
extends QtJambiObject
implements QGraphicsLayoutItemInterface

The QGraphicsLayout class provides the base class for all layouts in Graphics View. QGraphicsLayout is an abstract class that defines a virtual API for arranging QGraphicsWidget children and other QGraphicsLayoutItem objects for a QGraphicsWidget. QGraphicsWidget assigns responsibility to a QGraphicsLayout through QGraphicsWidget::setLayout(). As the widget is resized, the layout will automatically arrange the widget's children. QGraphicsLayout inherits QGraphicsLayoutItem, so, it can be managed by any layout, including its own subclasses.

Writing a Custom Layout

You can use QGraphicsLayout as a base to write your own custom layout (e.g., a flowlayout), but it is more common to use one of its subclasses instead - QGraphicsLinearLayout or QGraphicsGridLayout. When creating a custom layout, the following functions must be reimplemented as a bare minimum:

Function	Description
QGraphicsLayoutItem::setGeometry()	Notifies you when the geometry of the layout is set. You can store the geometry in your own layout class in a reimplementation of this function.
QGraphicsLayoutItem::sizeHint()	Returns the layout's size hints.
QGraphicsLayout::count()	Returns the number of items in your layout.
QGraphicsLayout::itemAt()	Returns a pointer to an item in your layout.
QGraphicsLayout::removeAt()	Removes an item from your layout without destroying it.

For more details on how to implement each function, refer to the individual function documentation.

Each layout defines its own API for arranging widgets and layout items. For example, with a grid layout, you require a row and a column index with optional row and column spans, alignment, spacing, and more. A linear layout, however, requires a single row or column index to position its items. For a grid layout, the order of insertion does not affect the layout in any way, but for a linear layout, the order is essential. When writing your own layout subclass, you are free to choose the API that best suits your layout.

Activating the Layout

When the layout's geometry changes, QGraphicsLayout immediately rearranges all of its managed items by calling setGeometry() on each item. This rearrangement is called activating the layout.

QGraphicsLayout updates its own geometry to match the contentsRect() of the QGraphicsLayoutItem it is managing. Thus, it will automatically rearrange all its items when the widget is resized. QGraphicsLayout caches the sizes of all its managed items to avoid calling setGeometry() too often.

Note: A QGraphicsLayout will have the same geometry as the contentsRect() of the widget (not the layout) it is assigned to.

Activating the Layout Implicitly

The layout can be activated implicitly using one of two ways: by calling activate() or by calling invalidate(). Calling activate() activates the layout immediately. In contrast, calling invalidate() is delayed, as it posts a LayoutRequest event to the managed widget. Due to event compression, the activate() will only be called once after control has returned to the event loop. This is referred to as invalidating the layout. Invalidating the layout also invalidates any cached information. Also, the invalidate() function is a virtual function. So, you can invalidate your own cache in a subclass of QGraphicsLayout by reimplementing this function.

Event Handling

QGraphicsLayout listens to events for the widget it manages through the virtual widgetEvent() event handler. When the layout is assigned to a widget, all events delivered to the widget are first processed by widgetEvent(). This allows the layout to be aware of any relevant state changes on the widget such as visibility changes or layout direction changes.

Margin Handling

The margins of a QGraphicsLayout can be modified by reimplementing setContentsMargins() and getContentsMargins().

Nested Class Summary

Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter

QSignalEmitter.AbstractSignal, 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

QGraphicsLayout()
Contructs a QGraphicsLayout object.

QGraphicsLayout(QGraphicsLayoutItemInterface parent)
Contructs a QGraphicsLayout object.

Method Summary

void	activate() Activates the layout, causing all items in the layout to be immediately rearranged.
QRectF	contentsRect() Returns the contents rect in local coordinates.
abstract int	count() This pure virtual function must be reimplemented in a subclass of QGraphicsLayout to return the number of items in the layout.
QSizeF	effectiveSizeHint(Qt.SizeHint which, QSizeF constraint) Returns the effective size hint for this QGraphicsLayoutItem.
QRectF	geometry() Returns the item's geometry (e.
com.trolltech.qt.gui.QMarginsF	getContentsMargins() This virtual function provides the left, top, right and bottom contents margins for this QGraphicsLayoutItem.
void	invalidate() Clears any cached geometry and size hint information in the layout, and posts a LayoutRequest event to the managed parent QGraphicsLayoutItem.
boolean	isActivated() Returns true if the layout is currently being activated; otherwise, returns false.
boolean	isLayout() Returns true if this QGraphicsLayoutItem is a layout (e.g., is inherited by an object that arranges other QGraphicsLayoutItem objects); otherwise returns false.
abstract QGraphicsLayoutItemInterface	itemAt(int i) This pure virtual function must be reimplemented in a subclass of QGraphicsLayout to return a pointer to the item at index i.
double	maximumHeight() Returns the maximum height.
QSizeF	maximumSize() Returns the maximum size.
double	maximumWidth() Returns the maximum width.
double	minimumHeight() Returns the minimum height.
QSizeF	minimumSize() Returns the minimum size.
double	minimumWidth() Returns the minimum width.
QGraphicsLayoutItemInterface	parentLayoutItem() Returns the parent of this QGraphicsLayoutItem, or 0 if there is no parent, or if the parent does not inherit from QGraphicsLayoutItem (QGraphicsLayoutItem is often used through multiple inheritance with QObject-derived classes).
double	preferredHeight() Returns the preferred height.
QSizeF	preferredSize() Returns the preferred size.
double	preferredWidth() Returns the preferred width.
abstract void	removeAt(int index) This pure virtual function must be reimplemented in a subclass of QGraphicsLayout to remove the item at index, index, without destroying it.
void	setContentsMargins(double left, double top, double right, double bottom) Sets the contents margins to left, top, right and bottom.
void	setGeometry(QRectF rect) This pure virtual function sets the geometry of the QGraphicsLayoutItem to rect, which is in parent coordinates (e.g., the top-left corner of rect is equivalent to the item's position in parent coordinates).
void	setMaximumHeight(double height) Sets the maximum height to height.
void	setMaximumSize(double w, double h) This convenience function is equivalent to calling setMaximumSize(QSizeF(w, h)).
void	setMaximumSize(QSizeF size) Sets the maximum size to size.
void	setMaximumWidth(double width) Sets the maximum width to width.
void	setMinimumHeight(double height) Sets the minimum height to height.
void	setMinimumSize(double w, double h) This convenience function is equivalent to calling setMinimumSize(QSizeF(w, h)).
void	setMinimumSize(QSizeF size) Sets the minimum size to size.
void	setMinimumWidth(double width) Sets the minimum width to width.
void	setParentLayoutItem(QGraphicsLayoutItemInterface parent) Sets the parent of this QGraphicsLayoutItem to parent.
void	setPreferredHeight(double height) Sets the preferred height to height.
void	setPreferredSize(double w, double h) This convenience function is equivalent to calling setPreferredSize(QSizeF(w, h)).
void	setPreferredSize(QSizeF size) Sets the preferred size to size.
void	setPreferredWidth(double width) Sets the preferred width to width.
void	setSizePolicy(QSizePolicy.Policy hPolicy, QSizePolicy.Policy vPolicy, QSizePolicy.ControlType controlType) This function is equivalent to calling setSizePolicy(QSizePolicy(hPolicy, vPolicy, controlType)).
void	setSizePolicy(QSizePolicy policy) Sets the size policy to policy.
abstract QSizeF	sizeHint(Qt.SizeHint which, QSizeF constraint) This pure virtual function returns the size hint for which of the QGraphicsLayoutItem, using the width or height of constraint to constrain the output.
QSizePolicy	sizePolicy() Returns the current size policy.
void	updateGeometry() This virtual function discards any cached size hint information.
void	widgetEvent(QEvent e) This virtual event handler receives all events for the managed widget.

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, toString, wait, wait, wait

Methods inherited from interface com.trolltech.qt.QtJambiInterface

disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership

Constructor Detail

QGraphicsLayout

public QGraphicsLayout()

Contructs a QGraphicsLayout object.

parent is passed to QGraphicsLayoutItem's constructor and the QGraphicsLayoutItem's isLayout argument is set to true.

QGraphicsLayout

public QGraphicsLayout(QGraphicsLayoutItemInterface parent)

Contructs a QGraphicsLayout object.

parent is passed to QGraphicsLayoutItem's constructor and the QGraphicsLayoutItem's isLayout argument is set to true.

Method Detail

activate

public final void activate()

Activates the layout, causing all items in the layout to be immediately rearranged. This function is based on calling count() and itemAt(), and then calling setGeometry() on all items sequentially. When activated, the layout will adjust its geometry to its parent's contentsRect(). The parent will then invalidate any layout of its own.

If called in sequence or recursively, e.g., by one of the arranged items in response to being resized, this function will do nothing.

Note that the layout is free to use geometry caching to optimize this process. To forcefully invalidate any such cache, you can call invalidate() before calling activate().

See also:

invalidate().

contentsRect

public final QRectF contentsRect()

Returns the contents rect in local coordinates.

The contents rect defines the subrectangle used by an associated layout when arranging subitems. This function is a convenience function that adjusts the item's geometry() by its contents margins. Note that getContentsMargins() is a virtual function that you can reimplement to return the item's contents margins.

See also:

getContentsMargins(), and geometry().

Specified by:

contentsRect in interface QGraphicsLayoutItemInterface

effectiveSizeHint

public final QSizeF effectiveSizeHint(Qt.SizeHint which,
                                      QSizeF constraint)

Returns the effective size hint for this QGraphicsLayoutItem.

which is the size hint in question. constraint is an optional argument that defines a special constrain when calculating the effective size hint. By default, constraint is QSizeF(-1, -1), which means there is no constraint to the size hint.

If you want to specify the widget's size hint for a given width or height, you can provide the fixed dimension in constraint. This is useful for widgets that can grow only either vertically or horizontally, and need to set either their width or their height to a special value.

For example, a text paragraph item fit into a column width of 200 may grow vertically. You can pass QSizeF(200, -1) as a constraint to get a suitable minimum, preferred and maximum height).

You can adjust the effective size hint by reimplementing sizeHint() in a QGraphicsLayoutItem subclass, or by calling one of the following functions: setMinimumSize(), setPreferredSize, or setMaximumSize() (or a combination of both).

This function caches each of the size hints and guarantees that sizeHint() will be called only once for each value of which - unless constraint is not specified and updateGeometry() has been called.

See also:

sizeHint().

Specified by:

effectiveSizeHint in interface QGraphicsLayoutItemInterface

geometry

public final QRectF geometry()

Returns the item's geometry (e. ., position and size) as a QRectF. This function is equivalent to QRectF(pos(), size()).

See also:

setGeometry().

Specified by:

geometry in interface QGraphicsLayoutItemInterface

isActivated

public final boolean isActivated()

Returns true if the layout is currently being activated; otherwise, returns false. If the layout is being activated, this means that it is currently in the process of rearranging its items (i.e., the activate() function has been called, and has not yet returned).

See also:

activate(), and invalidate().

isLayout

public final boolean isLayout()

Returns true if this QGraphicsLayoutItem is a layout (e.g., is inherited by an object that arranges other QGraphicsLayoutItem objects); otherwise returns false.

See also:

QGraphicsLayout.

Specified by:

isLayout in interface QGraphicsLayoutItemInterface

maximumHeight

public final double maximumHeight()

Returns the maximum height.

See also:

setMaximumHeight(), setMaximumSize(), and maximumSize().

Specified by:

maximumHeight in interface QGraphicsLayoutItemInterface

maximumSize

public final QSizeF maximumSize()

Returns the maximum size.

See also:

setMaximumSize(), minimumSize(), preferredSize(), Qt::MaximumSize , and sizeHint().

Specified by:

maximumSize in interface QGraphicsLayoutItemInterface

maximumWidth

public final double maximumWidth()

Returns the maximum width.

See also:

setMaximumWidth(), setMaximumSize(), and maximumSize().

Specified by:

maximumWidth in interface QGraphicsLayoutItemInterface

minimumHeight

public final double minimumHeight()

Returns the minimum height.

See also:

setMinimumHeight(), setMinimumSize(), and minimumSize().

Specified by:

minimumHeight in interface QGraphicsLayoutItemInterface

minimumSize

public final QSizeF minimumSize()

Returns the minimum size.

See also:

setMinimumSize(), preferredSize(), maximumSize(), Qt::MinimumSize , and sizeHint().

Specified by:

minimumSize in interface QGraphicsLayoutItemInterface

minimumWidth

public final double minimumWidth()

Returns the minimum width.

See also:

setMinimumWidth(), setMinimumSize(), and minimumSize().

Specified by:

minimumWidth in interface QGraphicsLayoutItemInterface

parentLayoutItem

public final QGraphicsLayoutItemInterface parentLayoutItem()

Returns the parent of this QGraphicsLayoutItem, or 0 if there is no parent, or if the parent does not inherit from QGraphicsLayoutItem (QGraphicsLayoutItem is often used through multiple inheritance with QObject-derived classes).

See also:

setParentLayoutItem().

Specified by:

parentLayoutItem in interface QGraphicsLayoutItemInterface

preferredHeight

public final double preferredHeight()

Returns the preferred height.

See also:

setPreferredHeight(), setPreferredSize(), and preferredSize().

Specified by:

preferredHeight in interface QGraphicsLayoutItemInterface

preferredSize

public final QSizeF preferredSize()

Returns the preferred size.

See also:

setPreferredSize(), minimumSize(), maximumSize(), Qt::PreferredSize , and sizeHint().

Specified by:

preferredSize in interface QGraphicsLayoutItemInterface

preferredWidth

public final double preferredWidth()

Returns the preferred width.

See also:

setPreferredWidth(), setPreferredSize(), and preferredSize().

Specified by:

preferredWidth in interface QGraphicsLayoutItemInterface

setContentsMargins

public final void setContentsMargins(double left,
                                     double top,
                                     double right,
                                     double bottom)

Sets the contents margins to left, top, right and bottom. The default contents margins for toplevel layouts are style dependent (by querying the pixelMetric for QStyle::PM_LayoutLeftMargin , QStyle::PM_LayoutTopMargin , QStyle::PM_LayoutRightMargin and QStyle::PM_LayoutBottomMargin ).

For sublayouts the default margins are 0.

Changing the contents margins automatically invalidates the layout.

See also:

invalidate().

setMaximumHeight

public final void setMaximumHeight(double height)

Sets the maximum height to height.

See also:

maximumHeight(), setMaximumSize(), and maximumSize().

Specified by:

setMaximumHeight in interface QGraphicsLayoutItemInterface

setMaximumSize

public final void setMaximumSize(QSizeF size)

Sets the maximum size to size. This property overrides sizeHint() for Qt::MaximumSize and ensures that effectiveSizeHint() will never return a size larger than size. In order to unset the maximum size, use an invalid size.

See also:

maximumSize(), minimumSize(), preferredSize(), Qt::MaximumSize , and sizeHint().

Specified by:

setMaximumSize in interface QGraphicsLayoutItemInterface

setMaximumSize

public final void setMaximumSize(double w,
                                 double h)

This convenience function is equivalent to calling setMaximumSize(QSizeF(w, h)).

See also:

maximumSize(), setMinimumSize(), setPreferredSize(), and sizeHint().

Specified by:

setMaximumSize in interface QGraphicsLayoutItemInterface

setMaximumWidth

public final void setMaximumWidth(double width)

Sets the maximum width to width.

See also:

maximumWidth(), setMaximumSize(), and maximumSize().

Specified by:

setMaximumWidth in interface QGraphicsLayoutItemInterface

setMinimumHeight

public final void setMinimumHeight(double height)

Sets the minimum height to height.

See also:

minimumHeight(), setMinimumSize(), and minimumSize().

Specified by:

setMinimumHeight in interface QGraphicsLayoutItemInterface

setMinimumSize

public final void setMinimumSize(QSizeF size)

Sets the minimum size to size. This property overrides sizeHint() for Qt::MinimumSize and ensures that effectiveSizeHint() will never return a size smaller than size. In order to unset the minimum size, use an invalid size.

See also:

minimumSize(), maximumSize(), preferredSize(), Qt::MinimumSize , sizeHint(), setMinimumWidth(), and setMinimumHeight().

Specified by:

setMinimumSize in interface QGraphicsLayoutItemInterface

setMinimumSize

public final void setMinimumSize(double w,
                                 double h)

This convenience function is equivalent to calling setMinimumSize(QSizeF(w, h)).

See also:

minimumSize(), setMaximumSize(), setPreferredSize(), and sizeHint().

Specified by:

setMinimumSize in interface QGraphicsLayoutItemInterface

setMinimumWidth

public final void setMinimumWidth(double width)

Sets the minimum width to width.

See also:

minimumWidth(), setMinimumSize(), and minimumSize().

Specified by:

setMinimumWidth in interface QGraphicsLayoutItemInterface

setParentLayoutItem

public final void setParentLayoutItem(QGraphicsLayoutItemInterface parent)

Sets the parent of this QGraphicsLayoutItem to parent.

See also:

parentLayoutItem().

Specified by:

setParentLayoutItem in interface QGraphicsLayoutItemInterface

setPreferredHeight

public final void setPreferredHeight(double height)

Sets the preferred height to height.

See also:

preferredHeight(), preferredWidth(), setPreferredSize(), and preferredSize().

Specified by:

setPreferredHeight in interface QGraphicsLayoutItemInterface

setPreferredSize

public final void setPreferredSize(QSizeF size)

Sets the preferred size to size. This property overrides sizeHint() for Qt::PreferredSize and provides the default value for effectiveSizeHint(). In order to unset the preferred size, use an invalid size.

See also:

preferredSize(), minimumSize(), maximumSize(), Qt::PreferredSize , and sizeHint().

Specified by:

setPreferredSize in interface QGraphicsLayoutItemInterface

setPreferredSize

public final void setPreferredSize(double w,
                                   double h)

This convenience function is equivalent to calling setPreferredSize(QSizeF(w, h)).

See also:

preferredSize(), setMaximumSize(), setMinimumSize(), and sizeHint().

Specified by:

setPreferredSize in interface QGraphicsLayoutItemInterface

setPreferredWidth

public final void setPreferredWidth(double width)

Sets the preferred width to width.

See also:

preferredWidth(), preferredHeight(), setPreferredSize(), and preferredSize().

Specified by:

setPreferredWidth in interface QGraphicsLayoutItemInterface

setSizePolicy

public final void setSizePolicy(QSizePolicy.Policy hPolicy,
                                QSizePolicy.Policy vPolicy,
                                QSizePolicy.ControlType controlType)

This function is equivalent to calling setSizePolicy(QSizePolicy(hPolicy, vPolicy, controlType)).

See also:

sizePolicy(), and QWidget::sizePolicy().

Specified by:

setSizePolicy in interface QGraphicsLayoutItemInterface

setSizePolicy

public final void setSizePolicy(QSizePolicy policy)

Sets the size policy to policy. The size policy describes how the item should grow horizontally and vertically when arranged in a layout.

QGraphicsLayoutItem's default size policy is (QSizePolicy::Fixed , QSizePolicy::Fixed , QSizePolicy::DefaultType ), but it is common for subclasses to change the default. For example, QGraphicsWidget defaults to (QSizePolicy::Preferred , QSizePolicy::Preferred , QSizePolicy::DefaultType ).

See also:

sizePolicy(), and QWidget::sizePolicy().

Specified by:

setSizePolicy in interface QGraphicsLayoutItemInterface

sizePolicy

public final QSizePolicy sizePolicy()

Returns the current size policy.

See also:

setSizePolicy(), and QWidget::sizePolicy().

Specified by:

sizePolicy in interface QGraphicsLayoutItemInterface

count

public abstract int count()

This pure virtual function must be reimplemented in a subclass of QGraphicsLayout to return the number of items in the layout.

The subclass is free to decide how to store the items.

See also:

itemAt(), and removeAt().

invalidate

public void invalidate()

Clears any cached geometry and size hint information in the layout, and posts a LayoutRequest event to the managed parent QGraphicsLayoutItem.

See also:

activate(), and setGeometry().

itemAt

public abstract QGraphicsLayoutItemInterface itemAt(int i)

This pure virtual function must be reimplemented in a subclass of QGraphicsLayout to return a pointer to the item at index i. The reimplementation can assume that i is valid (i.e., it respects the value of count()).

The subclass is free to decide how to store the items.

See also:

count(), and removeAt().

removeAt

public abstract void removeAt(int index)

This pure virtual function must be reimplemented in a subclass of QGraphicsLayout to remove the item at index, index, without destroying it. The reimplementation can assume that index is valid (i.e., it respects the value of count()).

The subclass is free to decide how to store the items.

See also:

itemAt(), and count().

setGeometry

public void setGeometry(QRectF rect)

This pure virtual function sets the geometry of the QGraphicsLayoutItem to rect, which is in parent coordinates (e.g., the top-left corner of rect is equivalent to the item's position in parent coordinates).

Reimplement this function in a subclass of QGraphicsLayoutItem to enable your item to receive geometry updates.

If rect is outside of the bounds of minimumSize and maximumSize, it will be adjusted to its closest size so that it is within the legal bounds.

See also:

geometry().

Specified by:

setGeometry in interface QGraphicsLayoutItemInterface

sizeHint

public abstract QSizeF sizeHint(Qt.SizeHint which,
                                QSizeF constraint)

This pure virtual function returns the size hint for which of the QGraphicsLayoutItem, using the width or height of constraint to constrain the output.

Reimplement this function in a subclass of QGraphicsLayoutItem to provide the necessary size hints for your items.

See also:

effectiveSizeHint().

Specified by:

sizeHint in interface QGraphicsLayoutItemInterface

updateGeometry

public void updateGeometry()

This virtual function discards any cached size hint information. You should always call this function if you change the return value of the sizeHint() function. Subclasses must always call the base implementation when reimplementing this function.

See also:

effectiveSizeHint().

Specified by:

updateGeometry in interface QGraphicsLayoutItemInterface

widgetEvent

public void widgetEvent(QEvent e)

This virtual event handler receives all events for the managed widget. QGraphicsLayout uses this event handler to listen for layout related events such as geometry changes, layout changes or layout direction changes.

e is a pointer to the event.

You can reimplement this event handler to track similar events for your own custom layout.

See also:

QGraphicsWidget::event(), and QGraphicsItem::sceneEvent().

getContentsMargins

public final com.trolltech.qt.gui.QMarginsF getContentsMargins()

This virtual function provides the left, top, right and bottom contents margins for this QGraphicsLayoutItem. The default implementation assumes all contents margins are 0. The parameters point to values stored in qreals. If any of the pointers is 0, that value will not be updated.

See also:

QGraphicsWidget::setContentsMargins().

Specified by:

getContentsMargins in interface QGraphicsLayoutItemInterface