Qt Quick 2 Legend Example▲
The Qt Quick 2 legend example shows how to make an interactive legend for a graph.
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 Qt Quick 2 Scatter Example.
Running the Example▲
To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.
Legend▲
The legend is simply a column of custom LegendItem items inside a transparent rectangle. Each item is supplied with a series and the graph theme:
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
}
}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:
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
}
}
}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.
The highlight depends on the selection state of the series, so we define two states, which follow the Bar3DSeries::selectedBar property and adjust the legendItem color appropriately:
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
}
}
]To make the legend item interactive, we define a MouseArea to detect clicks on it and adjust the series selection accordingly:
MouseArea {
id: mouseArea
anchors.fill: legendItem
onClicked: {
if (legendItem.state === "selected") {
series.selectedBar = series.invalidSelectionPosition
} else {
series.selectedBar = previousSelection
}
}
}The previousSelection used above is another custom property of LegendItem, which we update whenever selection changes on the series. This way we remember the last selected bar of each series:
Connections {
target: series
function onSelectedBarChanged(position) {
if (position !== series.invalidSelectionPosition) {
previousSelection = position
}
}
}