QLayoutItem Class

Member Function Documentation

QLayoutItem::QLayoutItem(Qt::Alignment alignment = Qt::Alignment())

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

[virtual] QLayoutItem::~QLayoutItem()

Destroys the QLayoutItem.

Qt::Alignment QLayoutItem::alignment() const

Returns the alignment of this item.

See also setAlignment().

[virtual] QSizePolicy::ControlTypes QLayoutItem::controlTypes() const

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().

[pure virtual] Qt::Orientations QLayoutItem::expandingDirections() const

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.

[pure virtual] QRect QLayoutItem::geometry() const

Returns the rectangle covered by this layout item.

See also setGeometry().

[virtual] bool QLayoutItem::hasHeightForWidth() const

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().

[virtual] int QLayoutItem::heightForWidth(int w) const

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().

[virtual] void QLayoutItem::invalidate()

Invalidates any cached information in this layout item.

[pure virtual] bool QLayoutItem::isEmpty() const

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

[virtual] QLayout *QLayoutItem::layout()

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

See also spacerItem() and widget().

[pure virtual] QSize QLayoutItem::maximumSize() const

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

[virtual] int QLayoutItem::minimumHeightForWidth(int w) const

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

[pure virtual] QSize QLayoutItem::minimumSize() const

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

void QLayoutItem::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().

[pure virtual] void QLayoutItem::setGeometry(const QRect &r)

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

See also geometry().

[pure virtual] QSize QLayoutItem::sizeHint() const

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

[virtual] QSpacerItem *QLayoutItem::spacerItem()

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

See also layout() and widget().

[virtual] QWidget *QLayoutItem::widget()

If this item manages a QWidget, returns that widget. Otherwise, nullptr is returned.

Note: While the functions layout() and spacerItem() perform casts, this function returns another object: QLayout and QSpacerItem inherit QLayoutItem, while QWidget does not.

See also layout() and spacerItem().