QLayoutItem Class

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# QLayoutItem Class Reference

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

`#include <qlayout.h>`

Inherited by QLayout, QSpacerItem, and QWidgetItem.

List of all member functions.

## Public Members

- QLayoutItem ( int alignment = 0 )
- virtual ~QLayoutItem ()
- virtual QSize sizeHint () const = 0
- virtual QSize minimumSize () const = 0
- virtual QSize maximumSize () const = 0
- virtual QSizePolicy::ExpandData expanding () const = 0
- virtual void setGeometry ( const QRect & r ) = 0
- virtual QRect geometry () const = 0
- virtual bool isEmpty () const = 0
- virtual bool hasHeightForWidth () const
- virtual int heightForWidth ( int w ) const
- virtual void invalidate ()
- virtual QWidget * widget ()
- virtual QLayoutIterator iterator ()
- virtual QLayout * layout ()
- virtual QSpacerItem * spacerItem ()
- int alignment () const
- virtual void setAlignment ( int a )

## 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. Copyright © 1995-2003 Trolltech. All Rights Reserved.