QGraphicsLayout Class Reference
[QtGui module]

Margin Handling

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

Member Function Documentation

QGraphicsLayout::QGraphicsLayout ( QGraphicsLayoutItem * parent = 0 )

Contructs a QGraphicsLayout object.

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

QGraphicsLayout::~QGraphicsLayout ()

Destroys the QGraphicsLayout object.

void QGraphicsLayout::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().

int QGraphicsLayout::count () const   [pure virtual]

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().

void QGraphicsLayout::invalidate ()   [virtual]

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().

bool QGraphicsLayout::isActivated () const

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().

QGraphicsLayoutItem * QGraphicsLayout::itemAt ( int i ) const   [pure virtual]

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().

void QGraphicsLayout::removeAt ( int index )   [pure virtual]

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

The implementation must ensure that the parentLayoutItem() of the removed item does not point to this layout, since the item is considered to be removed from the layout hierarchy.

If the layout is to be reused between applications, we recommend that the layout deletes the item, but the graphics view framework does not depend on this.

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

See also itemAt() and count().

void QGraphicsLayout::setContentsMargins ( qreal left, qreal top, qreal right, qreal 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().

void QGraphicsLayout::widgetEvent ( QEvent * e )   [virtual]

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().