This example shows how to create a reusable switch component in QML.
The code for this example can be found in the examples/quick/customitems/slideswitch
directory.
The objects that compose the switch are:
on
property (the interface to interact with the switch),toggle()
and dorelease()
),import QtQuick 2.0 Item { id: toggleswitch width: background.width; height: background.height property bool on: false function toggle() { if (toggleswitch.state == "on") toggleswitch.state = "off"; else toggleswitch.state = "on"; } function releaseSwitch() { if (knob.x == 1) { if (toggleswitch.state == "off") return; } if (knob.x == 78) { if (toggleswitch.state == "on") return; } toggle(); } Image { id: background source: "background.png" MouseArea { anchors.fill: parent; onClicked: toggle() } } Image { id: knob x: 1; y: 2 source: "knob.png" MouseArea { anchors.fill: parent drag.target: knob; drag.axis: Drag.XAxis; drag.minimumX: 1; drag.maximumX: 78 onClicked: toggle() onReleased: releaseSwitch() } } states: [ State { name: "on" PropertyChanges { target: knob; x: 78 } PropertyChanges { target: toggleswitch; on: true } }, State { name: "off" PropertyChanges { target: knob; x: 1 } PropertyChanges { target: toggleswitch; on: false } } ] transitions: Transition { NumberAnimation { properties: "x"; easing.type: Easing.InOutQuad; duration: 200 } } }
property bool on: false
This property is the interface of the switch. By default, the switch is off and this property is false
. It can be used to activate/deactivate the switch or to query its current state.
In this example:
Item { Switch { id: mySwitch on: true } Text { text: "The switch is on" visible: mySwitch.on == true } }
the text will only be visible when the switch is on.
Image { id: background source: "background.png" MouseArea { anchors.fill: parent; onClicked: toggle() } }
First, we create the background image of the switch. In order for the switch to toggle when the user clicks on the background, we add a MouseArea as a child item of the image. A
MouseArea
has a onClicked
property that is triggered when the item is clicked. For the moment we will just call a toggle()
function. We will see what this function does in a moment.
Image { id: knob x: 1; y: 2 source: "knob.png" MouseArea { anchors.fill: parent drag.target: knob; drag.axis: Drag.XAxis; drag.minimumX: 1; drag.maximumX: 78 onClicked: toggle() onReleased: releaseSwitch() } }
Then, we place the image of the knob on top of the background. The interaction here is a little more complex. We want the knob to move with the finger when it is clicked. That is what the drag
property of the
MouseArea
is for. We also want to toggle the switch if the knob is released between state. We handle this case in the dorelease()
function that is called in the onReleased
property.
states: [ State { name: "on" PropertyChanges { target: knob; x: 78 } PropertyChanges { target: toggleswitch; on: true } }, State { name: "off" PropertyChanges { target: knob; x: 1 } PropertyChanges { target: toggleswitch; on: false } } ]
We define the two states of the switch:
x
position is 78) and the on
property is true
.x
position is 1) and the on
property is false
.For more information on states see Qt Quick States.
We add two JavaScript functions to our switch:
function toggle() { if (toggleswitch.state == "on") toggleswitch.state = "off"; else toggleswitch.state = "on"; }
This first function is called when the background image or the knob are clicked. We simply want the switch to toggle between the two states (on and off).
function releaseSwitch() { if (knob.x == 1) { if (toggleswitch.state == "off") return; } if (knob.x == 78) { if (toggleswitch.state == "on") return; } toggle(); }
This second function is called when the knob is released and we want to make sure that the knob does not end up between states (neither on nor off). If it is the case call the toggle()
function
otherwise we do nothing.
For more information on scripts see JavaScript Expressions in QML Documents.
transitions: Transition { NumberAnimation { properties: "x"; easing.type: Easing.InOutQuad; duration: 200 } }
At this point, when the switch toggles between the two states the knob will instantly change its x
position between 1 and 78. In order for the knob to move smoothly we add a transition that will animate the
x
property with an easing curve for a duration of 200ms.
For more information on transitions see Animation and Transitions in Qt Quick.
The switch can be used in a QML file, like this:
Switch { anchors.centerIn: parent; on: false }