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<td >Qt 5.12</td><td ><a href="qtdatavisualization-index.html">Qt Data Visualization</a></td><td >Qt Quick 2 Legend Example</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right"><a href="qtdatavisualization-index.html">Qt Data Visualization | Commercial or GPLv3</a></td>
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<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#running-the-example">Running the Example</a></li>
<li class="level1"><a href="#legend">Legend</a></li>
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<h1 class="title">Qt Quick 2 Legend Example</h1>
<span class="subtitle"></span>
<!-- $$$qmllegend-brief -->
<p>Showing graph legend in a QML application.</p>
<!-- @@@qmllegend -->
<!-- $$$qmllegend-description -->
<div class="descr"> <a name="details"></a>
<p>The Qt Quick 2 legend example shows how to make an interactive legend for a graph.</p>
<p class="centerAlign"><img src="images/qmllegend-example.png" alt="" /></p><p>The interesting thing about this example is displaying the legend. We'll concentrate on that and skip explaining the basic functionality - for more detailed QML example documentation, see <a href="qtdatavisualization-qmlscatter-example.html">Qt Quick 2 Scatter Example</a>.</p>
<a name="running-the-example"></a>
<h2 id="running-the-example">Running the Example</h2>
<p>To run the example from Qt Creator, open the <b>Welcome</b> mode and select the example from <b>Examples</b>. For more information, visit Building and Running an Example.</p>
<a name="legend"></a>
<h2 id="legend">Legend</h2>
<p>The legend is simply a column of custom <code>LegendItem</code> items inside a transparent rectangle. Each item is supplied with a series and the graph theme:</p>
<pre class="qml">

  ColumnLayout {
      anchors.fill: parent
      anchors.margins: parent.border.width
      spacing: 0
      clip: true
      LegendItem {
          Layout.fillWidth: true
          Layout.fillHeight: true
          series: station1
          theme: barGraph.theme
      }
      LegendItem {
          Layout.fillWidth: true
          Layout.fillHeight: true
          series: station2
          theme: barGraph.theme
      }
      LegendItem {
          Layout.fillWidth: true
          Layout.fillHeight: true
          series: station3
          theme: barGraph.theme
      }
  }

</pre>
<p>The legend items consist of a marker rectangle, which indicates the color of the series, and a text field, which shows the name of the series. The colors we get from the series and the theme supplied at legend item initialization:</p>
<pre class="qml">

  property Theme3D theme
  property Bar3DSeries series
      ...
  RowLayout {
      anchors.fill: parent
      spacing: 0
      clip: true
      Item {
          id: markerSpace
          Layout.minimumWidth: 20
          Layout.minimumHeight: 20
          Layout.fillWidth: true
          Layout.fillHeight: true
          Layout.alignment: Qt.AlignVCenter
          Rectangle {
              x: parent.x + parent.width / 4
              y: parent.y + parent.height / 4
              width: parent.width / 2
              height: width
              border.color: "black"
              color: series.baseColor
          }
      }
      Item {
          height: markerSpace.height
          Layout.fillWidth: true
          Layout.fillHeight: true
          Layout.alignment: Qt.AlignVCenter
          Layout.minimumWidth: 100
          Text {
              anchors.fill: parent
              text: series.name
              verticalAlignment: Text.AlignVCenter
              clip: true
              color: theme.labelTextColor
              font: theme.font
          }
      }
  }

</pre>
<p>We want the legend to be interactive, so we add additional logic to enable selection of a series by clicking on a legend item, as well as highlighting the legend item corresponding to the selected series.</p>
<p>The highlight depends on the selection state of the series, so we define two states, which follow the <a href="qml-qtdatavisualization-bar3dseries.html#selectedBar-prop">Bar3DSeries::selectedBar</a> property and adjust the <code>legendItem</code> color appropriately:</p>
<pre class="qml">

  states: [
      State  {
          name: "selected"
          when: series.selectedBar != series.invalidSelectionPosition
          PropertyChanges {
              target: legendItem
              color: series.singleHighlightColor
          }
      },
      State  {
          name: "unselected"
          when: series.selectedBar == series.invalidSelectionPosition
          PropertyChanges {
              target: legendItem
              color: theme.labelBackgroundColor
          }
      }
  ]

</pre>
<p>To make the legend item interactive, we define a MouseArea to detect clicks on it and adjust the series selection accordingly:</p>
<pre class="qml">

  MouseArea {
      id: mouseArea
      anchors.fill: legendItem
      onClicked: {
          if (legendItem.state === "selected") {
              series.selectedBar = series.invalidSelectionPosition
          } else {
              series.selectedBar = previousSelection
          }
      }
  }

</pre>
<p>The <code>previousSelection</code> used above is another custom property of <code>LegendItem</code>, which we update whenever selection changes on the series. This way we remember the last selected bar of each series:</p>
<pre class="qml">

  Connections {
      target: series
      onSelectedBarChanged: {
          if (position != series.invalidSelectionPosition) {
              previousSelection = position
          }
      }
  }

</pre>
<p>Files:</p>
<ul>
<li><a href="qtdatavisualization-qmllegend-main-cpp.html">qmllegend/main.cpp</a></li>
<li><a href="qtdatavisualization-qmllegend-qml-qmllegend-data-qml.html">qmllegend/qml/qmllegend/Data.qml</a></li>
<li><a href="qtdatavisualization-qmllegend-qml-qmllegend-legenditem-qml.html">qmllegend/qml/qmllegend/LegendItem.qml</a></li>
<li><a href="qtdatavisualization-qmllegend-qml-qmllegend-newbutton-qml.html">qmllegend/qml/qmllegend/NewButton.qml</a></li>
<li><a href="qtdatavisualization-qmllegend-qml-qmllegend-main-qml.html">qmllegend/qml/qmllegend/main.qml</a></li>
<li><a href="qtdatavisualization-qmllegend-qmllegend-pro.html">qmllegend/qmllegend.pro</a></li>
<li><a href="qtdatavisualization-qmllegend-qmllegend-qrc.html">qmllegend/qmllegend.qrc</a></li>
</ul>
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