Detailed Description
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 is empty. iterator() returns
an iterator for the layout's children. If the concrete item is a
QWidget, it can be retrieved using widget(). Similarly for
layout() and spacerItem().
See also QLayout, Widget Appearance and Style and Layout Management.
Member Function Documentation
QLayoutItem::QLayoutItem ( int alignment = 0 )
Constructs a layout item with an alignment that is a bitwise OR
of the Qt::AlignmentFlags. Not all subclasses support
alignment.
QLayoutItem::~QLayoutItem () [virtual]
Destroys the QLayoutItem.
int QLayoutItem::alignment () const
Returns the alignment of this item.
QSizePolicy::ExpandData QLayoutItem::expanding () const [pure virtual]
Implemented in subclasses to return the direction(s) this item
"wants" to expand in (if any).
Reimplemented in QLayout, QSpacerItem and QWidgetItem.
QRect QLayoutItem::geometry () const [pure virtual]
Returns the rectangle covered by this layout item.
Example: customlayout/border.cpp.
bool QLayoutItem::hasHeightForWidth () const [virtual]
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().
Examples: customlayout/border.cpp and customlayout/flow.cpp.
Reimplemented in QGridLayout and QBoxLayout.
int QLayoutItem::heightForWidth ( int w ) const [virtual]
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().
Example: customlayout/flow.cpp.
Reimplemented in QGridLayout and QBoxLayout.
void QLayoutItem::invalidate () [virtual]
Invalidates any cached information in this layout item.
Reimplemented in QLayout.
bool QLayoutItem::isEmpty () const [pure virtual]
Implemented in subclasses to return whether this item is empty,
i.e. whether it contains any widgets.
Reimplemented in QLayout, QSpacerItem and QWidgetItem.
QLayoutIterator QLayoutItem::iterator () [virtual]
Returns an iterator over this item's QLayoutItem children. The
default implementation returns an empty iterator.
Reimplement this function in subclasses that can have children.
Reimplemented in QLayout.
QLayout * QLayoutItem::layout () [virtual]
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 () const [pure virtual]
Implemented in subclasses to return the maximum size of this item.
Reimplemented in QLayout, QSpacerItem and QWidgetItem.
QSize QLayoutItem::minimumSize () const [pure virtual]
Implemented in subclasses to return the minimum size of this item.
Examples: customlayout/border.cpp, customlayout/card.cpp and customlayout/flow.cpp.
Reimplemented in QLayout, QSpacerItem and QWidgetItem.
void QLayoutItem::setAlignment ( int a ) [virtual]
Sets the alignment of this item to a, which is a bitwise OR of
the Qt::AlignmentFlags. Not all subclasses support alignment.
Example: chart/optionsform.cpp.
void QLayoutItem::setGeometry ( const QRect & r ) [pure virtual]
Implemented in subclasses to set this item's geometry to r.
Examples: customlayout/border.cpp, customlayout/card.cpp and customlayout/flow.cpp.
Reimplemented in QLayout, QSpacerItem and QWidgetItem.
QSize QLayoutItem::sizeHint () const [pure virtual]
Implemented in subclasses to return the preferred size of this item.
Examples: customlayout/border.cpp, customlayout/card.cpp and customlayout/flow.cpp.
Reimplemented in QSpacerItem, QWidgetItem, QGridLayout and QBoxLayout.
QSpacerItem * QLayoutItem::spacerItem () [virtual]
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 () [virtual]
If this item is a QWidget, it is returned as a QWidget; otherwise
0 is returned. This function provides type-safe casting.
Reimplemented in QWidgetItem.
This file is part of the Qt toolkit.
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Trolltech. All Rights Reserved.
