Qt Reference Documentation

# QML Example - Toggle Switch

This example shows how to create a reusable switch component in QML.

The code for this example can be found in the `$QTDIR/examples/declarative/ui-components/slideswitch` directory.

The elements that composed the switch are:

- a `on` property (the interface to interact with the switch),
- two images (the background image and the knob),
- two mouse regions for user interation (on the background image and on the knob),
- two states (a on state and a off state),
- two functions or slots to react to the user interation (`toggle()` and `dorelease()`),
- and a transition that describe how to go from one state to the other.

## Switch.qml

     import QtQuick 1.0

     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.svg"
             MouseArea { anchors.fill: parent; onClicked: toggle() }
         }

         Image {
             id: knob
             x: 1; y: 2
             source: "knob.svg"

             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 }
         }
     }

## Walkthrough

### Interface

         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/disactivate 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.

### Images and user interaction

         Image {
             id: background
             source: "background.svg"
             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.svg"

             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

         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:

- In the on state the knob is on the right (`x` position is 78) and the `on` property is `true`.
- In the off state the knob is on the left (`x` position is 1) and the `on` property is `false`.

For more information on states see QML States.

### Functions

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 Integrating JavaScript.

### Transition

         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 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 QML Animation and Transitions.

## Usage

The switch can be used in a QML file, like this:

         Switch { anchors.centerIn: parent; on: false }