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QLayoutItem Class Reference
^{[QtGui module]}

The QLayoutItem class provides an abstract item that a QLayout manipulates. More...

Inherited by QLayout, QSpacerItem and QWidgetItem.

Methods

• __init__ (self, Qt.Alignment alignment = 0)
• __init__ (self, QLayoutItem)
• Qt.Alignment alignment (self)
• QSizePolicy.ControlTypes controlTypes (self)
• Qt.Orientations expandingDirections (self)
• QRect geometry (self)
• bool hasHeightForWidth (self)
• int heightForWidth (self, int)
• invalidate (self)
• bool isEmpty (self)
• QLayout layout (self)
• QSize maximumSize (self)
• int minimumHeightForWidth (self, int)
• QSize minimumSize (self)
• setAlignment (self, Qt.Alignment a)
• setGeometry (self, QRect)
• QSize sizeHint (self)
• QSpacerItem spacerItem (self)
• QWidget widget (self)

The QLayoutItem class provides an abstract item that a QLayout manipulates.

This is used by custom layouts.

Pure virtual functions are provided to return information about the layout, including, sizeHint(), minimumSize(), maximumSize() and expanding().

The layout's geometry can be set and retrieved with setGeometry() and geometry(), and its alignment with setAlignment() and alignment().

isEmpty() returns whether the layout item is empty. If the concrete item is a QWidget, it can be retrieved using widget(). Similarly for layout() and spacerItem().

Some layouts have width and height interdependencies. These can be expressed using hasHeightForWidth(), heightForWidth(), and minimumHeightForWidth(). For more explanation see the Qt Quarterly article Trading Height for Width.

Method Documentation

QLayoutItem.__init__ (self, Qt.Alignment alignment = 0)

Constructs a layout item with an alignment. Not all subclasses support alignment.

QLayoutItem.__init__ (self, QLayoutItem)

Qt.Alignment QLayoutItem.alignment (self)

Returns the alignment of this item.

See also setAlignment().

QSizePolicy.ControlTypes QLayoutItem.controlTypes (self)

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().

Qt.Orientations QLayoutItem.expandingDirections (self)

This method is abstract and should be reimplemented in any sub-class.

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.

QRect QLayoutItem.geometry (self)

This method is abstract and should be reimplemented in any sub-class.

Returns the rectangle covered by this layout item.

See also setGeometry().

bool QLayoutItem.hasHeightForWidth (self)

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

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

int QLayoutItem.heightForWidth (self, int)

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:

 int MyLayout.heightForWidth(int w) const
 {
     if (cache_dirty || cached_width != w) {
         // not all C++ compilers support "mutable"
         MyLayout *that = (MyLayout*)this;
         int h = calculateHeightForWidth(w);
         that->cached_hfw = h;
         return h;
     }
     return cached_hfw;
 }

Caching is strongly recommended; without it layout will take exponential time.

See also hasHeightForWidth().

QLayoutItem.invalidate (self)

Invalidates any cached information in this layout item.

bool QLayoutItem.isEmpty (self)

This method is abstract and should be reimplemented in any sub-class.

Implemented in subclasses to return whether this item is empty, i.e. whether it contains any widgets.

QLayout QLayoutItem.layout (self)

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

QSize QLayoutItem.maximumSize (self)

This method is abstract and should be reimplemented in any sub-class.

Implemented in subclasses to return the maximum size of this item.

int QLayoutItem.minimumHeightForWidth (self, int)

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

QSize QLayoutItem.minimumSize (self)

This method is abstract and should be reimplemented in any sub-class.

Implemented in subclasses to return the minimum size of this item.

QLayoutItem.setAlignment (self, Qt.Alignment a)

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().

QLayoutItem.setGeometry (self, QRect)

This method is abstract and should be reimplemented in any sub-class.

Implemented in subclasses to set this item's geometry to r.

See also geometry().

QSize QLayoutItem.sizeHint (self)

This method is abstract and should be reimplemented in any sub-class.

Implemented in subclasses to return the preferred size of this item.

QSpacerItem QLayoutItem.spacerItem (self)

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

QWidget QLayoutItem.widget (self)

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