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

# QwtAbstractLegend(3)

Abstract base class for legend widgets.

## NAME

QwtAbstractLegend - Abstract base class for legend widgets.

## SYNOPSIS

`#include <qwt_abstract_legend.h>`

Inherits QFrame.

Inherited by **QwtLegend**.

### Public Slots

virtual void **updateLegend** (const QVariant &itemInfo, const QList\< **QwtLegendData** \> &data)=0\
 Update the entries for a plot item.

### Public Member Functions

**QwtAbstractLegend** (QWidget \*parent=NULL)\
 virtual **~QwtAbstractLegend** ()\
 Destructor.  virtual void **renderLegend** (QPainter \*painter, const QRectF &rect, bool fillBackground) const =0\
 virtual bool **isEmpty** () const =0\
 virtual int **scrollExtent** (Qt::Orientation) const\

## Detailed Description

Abstract base class for legend widgets.

Legends, that need to be under control of the **QwtPlot** layout system need to be derived from **QwtAbstractLegend**.

**Note:**

Other type of legends can be implemented by connecting to the **QwtPlot::legendDataChanged()** signal. But as these legends are unknown to the plot layout system the layout code ( on screen and for **QwtPlotRenderer** ) need to be organized in application code.

**See also:**

**QwtLegend**

## Constructor & Destructor Documentation

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

Constructor

**Parameters:**

*parent* Parent widget

## Member Function Documentation

### virtual bool QwtAbstractLegend::isEmpty () const` [pure virtual]`

**Returns:**

True, when no plot item is inserted

Implemented in **QwtLegend**.

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

Implemented in **QwtLegend**.

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

Return the extent, that is needed for elements to scroll the legend ( usually scrollbars ),

**Parameters:**

*orientation* Orientation

**Returns:**

Extent of the corresponding scroll element

Reimplemented in **QwtLegend**.

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

Update the entries for a plot item.

**Parameters:**

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

## Author

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