---
name: "QwtLegend"
section: "3"
platform: "linux"
package: "libqwt-doc"
version: "6.1.4-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/QwtLegend"
---

# QwtLegend(3)

The legend widget.

## NAME

QwtLegend - The legend widget.

## SYNOPSIS

`#include <qwt_legend.h>`

Inherits **QwtAbstractLegend**.

### Public Slots

virtual void **updateLegend** (const QVariant &, const QList\< **QwtLegendData** \> &)\
 Update the entries for an item.

### Signals

void **clicked** (const QVariant &**itemInfo**, int index)\
 void **checked** (const QVariant &**itemInfo**, bool on, int index)\

### Public Member Functions

**QwtLegend** (QWidget \*parent=NULL)\
 virtual **~QwtLegend** ()\
 Destructor.  void **setMaxColumns** (uint numColums)\
 Set the maximum number of entries in a row.  uint **maxColumns** () const\
 void **setDefaultItemMode** (**QwtLegendData::Mode**)\
 Set the default mode for legend labels.  **QwtLegendData::Mode** **defaultItemMode** () const\
 QWidget \* **contentsWidget** ()\
 const QWidget \* **contentsWidget** () const\
 QWidget \* **legendWidget** (const QVariant &) const\
 QList\< QWidget \* \> **legendWidgets** (const QVariant &) const\
 QVariant **itemInfo** (const QWidget \*) const\
 virtual bool **eventFilter** (QObject \*, QEvent \*)\
 virtual QSize **sizeHint** () const\
 Return a size hint.  virtual int **heightForWidth** (int width) const\
 QScrollBar \* **horizontalScrollBar** () const\
 QScrollBar \* **verticalScrollBar** () const\
 virtual void **renderLegend** (QPainter \*, const QRectF &, bool fillBackground) const\
 virtual void **renderItem** (QPainter \*, const QWidget \*, const QRectF &, bool fillBackground) const\
 virtual bool **isEmpty** () const\
 virtual int **scrollExtent** (Qt::Orientation) const\

### Protected Slots

void **itemClicked** ()\
 void **itemChecked** (bool)\

### Protected Member Functions

virtual QWidget \* **createWidget** (const **QwtLegendData** &) const\
 Create a widget to be inserted into the legend.  virtual void **updateWidget** (QWidget \*widget, const **QwtLegendData** &)\
 Update the widget.

## Detailed Description

The legend widget.

The **QwtLegend** widget is a tabular arrangement of legend items. Legend items might be any type of widget, but in general they will be a **QwtLegendLabel**.

**See also:**

**QwtLegendLabel**, **QwtPlotItem**, **QwtPlot**

## Constructor & Destructor Documentation

### QwtLegend::QwtLegend (QWidget \* parent = `NULL`)` [explicit]`

Constructor

**Parameters:**

*parent* Parent widget

## Member Function Documentation

### void QwtLegend::checked (const QVariant & itemInfo, bool on, int index)` [signal]`

A signal which is emitted when the user has clicked on a legend label, which is in **QwtLegendData::Checkable** mode

**Parameters:**

*itemInfo* Info for the item of the selected legend label \
 *index* Index of the legend label in the list of widgets that are associated with the plot item \
 *on* True when the legend label is checked

**Note:**

clicks are disabled as default

**See also:**

**setDefaultItemMode()**, **defaultItemMode()**, **QwtPlot::itemToInfo()**

### void QwtLegend::clicked (const QVariant & itemInfo, int index)` [signal]`

A signal which is emitted when the user has clicked on a legend label, which is in **QwtLegendData::Clickable** mode.

**Parameters:**

*itemInfo* Info for the item item of the selected legend item \
 *index* Index of the legend label in the list of widgets that are associated with the plot item

**Note:**

clicks are disabled as default

**See also:**

**setDefaultItemMode()**, **defaultItemMode()**, **QwtPlot::itemToInfo()**

### QWidget \* QwtLegend::contentsWidget ()

The contents widget is the only child of the viewport of the internal QScrollArea and the parent widget of all legend items.

**Returns:**

Container widget of the legend items

### const QWidget \* QwtLegend::contentsWidget () const

The contents widget is the only child of the viewport of the internal QScrollArea and the parent widget of all legend items.

**Returns:**

Container widget of the legend items

### QWidget \* QwtLegend::createWidget (const QwtLegendData & legendData) const` [protected]`, ` [virtual]`

Create a widget to be inserted into the legend. The default implementation returns a **QwtLegendLabel**.

**Parameters:**

*legendData* Attributes of the legend entry

**Returns:**

Widget representing data on the legend

**Note:**

**updateWidget()** will called soon after **createWidget()** with the same attributes.

### QwtLegendData::Mode QwtLegend::defaultItemMode () const

**Returns:**

Default item mode

**See also:**

**setDefaultItemMode()**

### bool QwtLegend::eventFilter (QObject \* object, QEvent \* event)` [virtual]`

Handle QEvent::ChildRemoved andQEvent::LayoutRequest events for the **contentsWidget()**.

**Parameters:**

*object* Object to be filtered \
 *event* Event

**Returns:**

Forwarded to QwtAbstractLegend::eventFilter()

### int QwtLegend::heightForWidth (int width) const` [virtual]`

**Returns:**

The preferred height, for a width.

**Parameters:**

*width* Width

### QScrollBar \* QwtLegend::horizontalScrollBar () const

**Returns:**

Horizontal scrollbar

**See also:**

**verticalScrollBar()**

### bool QwtLegend::isEmpty () const` [virtual]`

**Returns:**

True, when no item is inserted

Implements **QwtAbstractLegend**.

### void QwtLegend::itemChecked (bool on)` [protected]`, ` [slot]`

Called internally when the legend has been checked Emits a **checked()** signal.

### void QwtLegend::itemClicked ()` [protected]`, ` [slot]`

Called internally when the legend has been clicked on. Emits a **clicked()** signal.

### QVariant QwtLegend::itemInfo (const QWidget \* widget) const

Find the item that is associated to a widget

**Parameters:**

*widget* Widget on the legend

**Returns:**

Associated item info

**See also:**

**legendWidget()**

### QWidget \* QwtLegend::legendWidget (const QVariant & itemInfo) const

**Returns:**

First widget in the list of widgets associated to an item

**Parameters:**

*itemInfo* Info about an item

**See also:**

**itemInfo()**, **QwtPlot::itemToInfo()**

**Note:**

Almost all types of items have only one widget

### QList\< QWidget \* \> QwtLegend::legendWidgets (const QVariant & itemInfo) const

**Returns:**

List of widgets associated to a item

**Parameters:**

*itemInfo* Info about an item

**See also:**

**legendWidget()**, **itemInfo()**, **QwtPlot::itemToInfo()**

### uint QwtLegend::maxColumns () const

**Returns:**

Maximum number of entries in a row

**See also:**

**setMaxColumns()**, **QwtDynGridLayout::maxColumns()**

### void QwtLegend::renderItem (QPainter \* painter, const QWidget \* widget, const QRectF & rect, bool fillBackground) const` [virtual]`

Render a legend entry into a given rectangle.

**Parameters:**

*painter* Painter \
 *widget* Widget representing a legend entry \
 *rect* Bounding rectangle \
 *fillBackground* When true, fill rect with the widget background

**Note:**

When widget is not derived from **QwtLegendLabel** renderItem does nothing beside the background

### void QwtLegend::renderLegend (QPainter \* painter, const QRectF & rect, bool fillBackground) const` [virtual]`

Render the legend into a given rectangle.

**Parameters:**

*painter* Painter \
 *rect* Bounding rectangle \
 *fillBackground* When true, fill rect with the widget background

**See also:**

**renderLegend()** is used by **QwtPlotRenderer** - not by **QwtLegend** itself

Implements **QwtAbstractLegend**.

### int QwtLegend::scrollExtent (Qt::Orientation orientation) const` [virtual]`

Return the extent, that is needed for the scrollbars

**Parameters:**

*orientation* Orientation

**Returns:**

The width of the vertical scrollbar for Qt::Horizontal and v.v.

Reimplemented from **QwtAbstractLegend**.

### void QwtLegend::setDefaultItemMode (QwtLegendData::Mode mode)

Set the default mode for legend labels. Legend labels will be constructed according to the attributes in a **QwtLegendData** object. When it doesn't contain a value for the QwtLegendData::ModeRole the label will be initialized with the default mode of the legend.

**Parameters:**

*mode* Default item mode

**See also:**

itemMode(), **QwtLegendData::value()**, **QwtPlotItem::legendData()**

**Note:**

Changing the mode doesn't have any effect on existing labels.

### void QwtLegend::setMaxColumns (uint numColums)

Set the maximum number of entries in a row. F.e when the maximum is set to 1 all items are aligned vertically. 0 means unlimited

**Parameters:**

*numColums* Maximum number of entries in a row

**See also:**

**maxColumns()**, **QwtDynGridLayout::setMaxColumns()**

### void QwtLegend::updateLegend (const QVariant & itemInfo, const QList\< QwtLegendData \> & legendData)` [virtual]`, ` [slot]`

Update the entries for an item.

**Parameters:**

*itemInfo* Info for an item \
 *legendData* List of legend entry attributes for the item

### void QwtLegend::updateWidget (QWidget \* widget, const QwtLegendData & legendData)` [protected]`, ` [virtual]`

Update the widget.

**Parameters:**

*widget* Usually a **QwtLegendLabel** \
 *legendData* Attributes to be displayed

**See also:**

**createWidget()**

**Note:**

When widget is no **QwtLegendLabel** **updateWidget()** does nothing.

### QScrollBar \* QwtLegend::verticalScrollBar () const

**Returns:**

Vertical scrollbar

**See also:**

**horizontalScrollBar()**

## Author

Generated automatically by Doxygen for Qwt User's Guide from the source code.