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<td >Qt 5.9</td><td ><a href="qtquick-index.html">Qt Quick</a></td><td >Qt Quick Examples - Toggle Switch</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right">Qt 5.9.4 Reference Documentation</td>
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<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#switch-qml">Switch.qml</a></li>
<li class="level1"><a href="#walkthrough">Walkthrough</a></li>
<li class="level2"><a href="#interface">Interface</a></li>
<li class="level2"><a href="#images-and-user-interaction">Images and User Interaction</a></li>
<li class="level2"><a href="#states">States</a></li>
<li class="level2"><a href="#functions">Functions</a></li>
<li class="level2"><a href="#transition">Transition</a></li>
<li class="level1"><a href="#usage">Usage</a></li>
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<h1 class="title">Qt Quick Examples - Toggle Switch</h1>
<span class="subtitle"></span>
<!-- $$$qmlexampletoggleswitch.html-description -->
<div class="descr"> <a name="details"></a>
<p>This example shows how to create a reusable switch component in QML.</p>
<p>The code for this example can be found in the <code>examples/quick/customitems/slideswitch</code> directory.</p>
<p>The objects that compose the switch are:</p>
<ul>
<li>a <code>on</code> property (the interface to interact with the switch),</li>
<li>two images (the background image and the knob),</li>
<li>two mouse regions for user interation (on the background image and on the knob),</li>
<li>two states (an <i>on</i> state and an <i>off</i> state),</li>
<li>two functions or slots to react to the user interation (<code>toggle()</code> and <code>dorelease()</code>),</li>
<li>and a transition that describe how to go from one state to the other.</li>
</ul>
<a name="switch-qml"></a>
<h2 id="switch-qml">Switch.qml</h2>
<pre class="qml">
import QtQuick 2.0
<span class="type"><a href="qml-qtquick-item.html">Item</a></span> {
<span class="name">id</span>: <span class="name">toggleswitch</span>
<span class="name">width</span>: <span class="name">background</span>.<span class="name">width</span>; <span class="name">height</span>: <span class="name">background</span>.<span class="name">height</span>
property <span class="type">bool</span> <span class="name">on</span>: <span class="number">false</span>
<span class="keyword">function</span> <span class="name">toggle</span>() {
<span class="keyword">if</span> (<span class="name">toggleswitch</span>.<span class="name">state</span> <span class="operator">==</span> <span class="string">"on"</span>)
<span class="name">toggleswitch</span>.<span class="name">state</span> <span class="operator">=</span> <span class="string">"off"</span>;
<span class="keyword">else</span>
<span class="name">toggleswitch</span>.<span class="name">state</span> <span class="operator">=</span> <span class="string">"on"</span>;
}
<span class="keyword">function</span> <span class="name">releaseSwitch</span>() {
<span class="keyword">if</span> (<span class="name">knob</span>.<span class="name">x</span> <span class="operator">==</span> <span class="number">1</span>) {
<span class="keyword">if</span> (<span class="name">toggleswitch</span>.<span class="name">state</span> <span class="operator">==</span> <span class="string">"off"</span>) <span class="keyword">return</span>;
}
<span class="keyword">if</span> (<span class="name">knob</span>.<span class="name">x</span> <span class="operator">==</span> <span class="number">78</span>) {
<span class="keyword">if</span> (<span class="name">toggleswitch</span>.<span class="name">state</span> <span class="operator">==</span> <span class="string">"on"</span>) <span class="keyword">return</span>;
}
<span class="name">toggle</span>();
}
<span class="type"><a href="qml-qtquick-image.html">Image</a></span> {
<span class="name">id</span>: <span class="name">background</span>
<span class="name">source</span>: <span class="string">"background.png"</span>
<span class="type"><a href="qml-qtquick-mousearea.html">MouseArea</a></span> { <span class="name">anchors</span>.fill: <span class="name">parent</span>; <span class="name">onClicked</span>: <span class="name">toggle</span>() }
}
<span class="type"><a href="qml-qtquick-image.html">Image</a></span> {
<span class="name">id</span>: <span class="name">knob</span>
<span class="name">x</span>: <span class="number">1</span>; <span class="name">y</span>: <span class="number">2</span>
<span class="name">source</span>: <span class="string">"knob.png"</span>
<span class="type"><a href="qml-qtquick-mousearea.html">MouseArea</a></span> {
<span class="name">anchors</span>.fill: <span class="name">parent</span>
<span class="name">drag</span>.target: <span class="name">knob</span>; <span class="name">drag</span>.axis: <span class="name">Drag</span>.<span class="name">XAxis</span>; <span class="name">drag</span>.minimumX: <span class="number">1</span>; <span class="name">drag</span>.maximumX: <span class="number">78</span>
<span class="name">onClicked</span>: <span class="name">toggle</span>()
<span class="name">onReleased</span>: <span class="name">releaseSwitch</span>()
}
}
<span class="name">states</span>: [
<span class="type"><a href="qml-qtquick-state.html">State</a></span> {
<span class="name">name</span>: <span class="string">"on"</span>
<span class="type"><a href="qml-qtquick-propertychanges.html">PropertyChanges</a></span> { <span class="name">target</span>: <span class="name">knob</span>; <span class="name">x</span>: <span class="number">78</span> }
<span class="type"><a href="qml-qtquick-propertychanges.html">PropertyChanges</a></span> { <span class="name">target</span>: <span class="name">toggleswitch</span>; <span class="name">on</span>: <span class="number">true</span> }
},
<span class="type"><a href="qml-qtquick-state.html">State</a></span> {
<span class="name">name</span>: <span class="string">"off"</span>
<span class="type"><a href="qml-qtquick-propertychanges.html">PropertyChanges</a></span> { <span class="name">target</span>: <span class="name">knob</span>; <span class="name">x</span>: <span class="number">1</span> }
<span class="type"><a href="qml-qtquick-propertychanges.html">PropertyChanges</a></span> { <span class="name">target</span>: <span class="name">toggleswitch</span>; <span class="name">on</span>: <span class="number">false</span> }
}
]
<span class="name">transitions</span>: <span class="name">Transition</span> {
<span class="type"><a href="qml-qtquick-numberanimation.html">NumberAnimation</a></span> { <span class="name">properties</span>: <span class="string">"x"</span>; <span class="name">easing</span>.type: <span class="name">Easing</span>.<span class="name">InOutQuad</span>; <span class="name">duration</span>: <span class="number">200</span> }
}
}
</pre>
<a name="walkthrough"></a>
<h2 id="walkthrough">Walkthrough</h2>
<a name="interface"></a>
<h3 >Interface</h3>
<pre class="qml">
property <span class="type">bool</span> <span class="name">on</span>: <span class="number">false</span>
</pre>
<p>This property is the interface of the switch. By default, the switch is off and this property is <code>false</code>. It can be used to activate/deactivate the switch or to query its current state.</p>
<p>In this example:</p>
<pre class="qml">
<span class="type"><a href="qml-qtquick-item.html">Item</a></span> {
<span class="type">Switch</span> {
<span class="name">id</span>: <span class="name">mySwitch</span>
<span class="name">on</span>: <span class="number">true</span>
}
<span class="type"><a href="qml-qtquick-text.html">Text</a></span> {
<span class="name">text</span>: <span class="string">"The switch is on"</span>
<span class="name">visible</span>: <span class="name">mySwitch</span>.<span class="name">on</span> <span class="operator">==</span> <span class="number">true</span>
}
}
</pre>
<p>the text will only be visible when the switch is on.</p>
<a name="images-and-user-interaction"></a>
<h3 >Images and User Interaction</h3>
<pre class="qml">
<span class="type"><a href="qml-qtquick-image.html">Image</a></span> {
<span class="name">id</span>: <span class="name">background</span>
<span class="name">source</span>: <span class="string">"background.png"</span>
<span class="type"><a href="qml-qtquick-mousearea.html">MouseArea</a></span> { <span class="name">anchors</span>.fill: <span class="name">parent</span>; <span class="name">onClicked</span>: <span class="name">toggle</span>() }
}
</pre>
<p>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 <a href="qml-qtquick-mousearea.html">MouseArea</a> as a child item of the image. A <code>MouseArea</code> has a <code>onClicked</code> property that is triggered when the item is clicked. For the moment we will just call a <code>toggle()</code> function. We will see what this function does in a moment.</p>
<pre class="qml">
<span class="type"><a href="qml-qtquick-image.html">Image</a></span> {
<span class="name">id</span>: <span class="name">knob</span>
<span class="name">x</span>: <span class="number">1</span>; <span class="name">y</span>: <span class="number">2</span>
<span class="name">source</span>: <span class="string">"knob.png"</span>
<span class="type"><a href="qml-qtquick-mousearea.html">MouseArea</a></span> {
<span class="name">anchors</span>.fill: <span class="name">parent</span>
<span class="name">drag</span>.target: <span class="name">knob</span>; <span class="name">drag</span>.axis: <span class="name">Drag</span>.<span class="name">XAxis</span>; <span class="name">drag</span>.minimumX: <span class="number">1</span>; <span class="name">drag</span>.maximumX: <span class="number">78</span>
<span class="name">onClicked</span>: <span class="name">toggle</span>()
<span class="name">onReleased</span>: <span class="name">releaseSwitch</span>()
}
}
</pre>
<p>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 <code>drag</code> property of the <code>MouseArea</code> is for. We also want to toggle the switch if the knob is released between state. We handle this case in the <code>dorelease()</code> function that is called in the <code>onReleased</code> property.</p>
<a name="states"></a>
<h3 >States</h3>
<pre class="qml">
<span class="name">states</span>: [
<span class="type"><a href="qml-qtquick-state.html">State</a></span> {
<span class="name">name</span>: <span class="string">"on"</span>
<span class="type"><a href="qml-qtquick-propertychanges.html">PropertyChanges</a></span> { <span class="name">target</span>: <span class="name">knob</span>; <span class="name">x</span>: <span class="number">78</span> }
<span class="type"><a href="qml-qtquick-propertychanges.html">PropertyChanges</a></span> { <span class="name">target</span>: <span class="name">toggleswitch</span>; <span class="name">on</span>: <span class="number">true</span> }
},
<span class="type"><a href="qml-qtquick-state.html">State</a></span> {
<span class="name">name</span>: <span class="string">"off"</span>
<span class="type"><a href="qml-qtquick-propertychanges.html">PropertyChanges</a></span> { <span class="name">target</span>: <span class="name">knob</span>; <span class="name">x</span>: <span class="number">1</span> }
<span class="type"><a href="qml-qtquick-propertychanges.html">PropertyChanges</a></span> { <span class="name">target</span>: <span class="name">toggleswitch</span>; <span class="name">on</span>: <span class="number">false</span> }
}
]
</pre>
<p>We define the two states of the switch:</p>
<ul>
<li>In the <i>on</i> state the knob is on the right (<code>x</code> position is 78) and the <code>on</code> property is <code>true</code>.</li>
<li>In the <i>off</i> state the knob is on the left (<code>x</code> position is 1) and the <code>on</code> property is <code>false</code>.</li>
</ul>
<p>For more information on states see <a href="qtquick-statesanimations-states.html">Qt Quick States</a>.</p>
<a name="functions"></a>
<h3 >Functions</h3>
<p>We add two JavaScript functions to our switch:</p>
<pre class="qml">
<span class="keyword">function</span> <span class="name">toggle</span>() {
<span class="keyword">if</span> (<span class="name">toggleswitch</span>.<span class="name">state</span> <span class="operator">==</span> <span class="string">"on"</span>)
<span class="name">toggleswitch</span>.<span class="name">state</span> <span class="operator">=</span> <span class="string">"off"</span>;
<span class="keyword">else</span>
<span class="name">toggleswitch</span>.<span class="name">state</span> <span class="operator">=</span> <span class="string">"on"</span>;
}
</pre>
<p>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 (<i>on</i> and <i>off</i>).</p>
<pre class="qml">
<span class="keyword">function</span> <span class="name">releaseSwitch</span>() {
<span class="keyword">if</span> (<span class="name">knob</span>.<span class="name">x</span> <span class="operator">==</span> <span class="number">1</span>) {
<span class="keyword">if</span> (<span class="name">toggleswitch</span>.<span class="name">state</span> <span class="operator">==</span> <span class="string">"off"</span>) <span class="keyword">return</span>;
}
<span class="keyword">if</span> (<span class="name">knob</span>.<span class="name">x</span> <span class="operator">==</span> <span class="number">78</span>) {
<span class="keyword">if</span> (<span class="name">toggleswitch</span>.<span class="name">state</span> <span class="operator">==</span> <span class="string">"on"</span>) <span class="keyword">return</span>;
}
<span class="name">toggle</span>();
}
</pre>
<p>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 <i>on</i> nor <i>off</i>). If it is the case call the <code>toggle()</code> function otherwise we do nothing.</p>
<p>For more information on scripts see JavaScript Expressions in QML Documents.</p>
<a name="transition"></a>
<h3 >Transition</h3>
<pre class="qml">
<span class="name">transitions</span>: <span class="name">Transition</span> {
<span class="type"><a href="qml-qtquick-numberanimation.html">NumberAnimation</a></span> { <span class="name">properties</span>: <span class="string">"x"</span>; <span class="name">easing</span>.type: <span class="name">Easing</span>.<span class="name">InOutQuad</span>; <span class="name">duration</span>: <span class="number">200</span> }
}
</pre>
<p>At this point, when the switch toggles between the two states the knob will instantly change its <code>x</code> position between 1 and 78. In order for the knob to move smoothly we add a transition that will animate the <code>x</code> property with an easing curve for a duration of 200ms.</p>
<p>For more information on transitions see <a href="qtquick-statesanimations-animations.html">Animation and Transitions in Qt Quick</a>.</p>
<a name="usage"></a>
<h2 id="usage">Usage</h2>
<p>The switch can be used in a QML file, like this:</p>
<pre class="qml">
<span class="type">Switch</span> { <span class="name">anchors</span>.centerIn: <span class="name">parent</span>; <span class="name">on</span>: <span class="number">false</span> }
</pre>
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