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<h1 class="title">QML Tutorial 3 - States and Transitions</h1>
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<p>In this chapter, we make this example a little bit more dynamic by introducing states and transitions.</p>
<p>We want our text to move to the bottom of the screen, rotate and become red when clicked.</p>
<p class="centerAlign"><img src="images/declarative-tutorial3_animation.gif" alt="" /></p><p>Here is the QML code:</p>
<pre class="qml">

  import QtQuick 2.0

  Rectangle {
      id: page
      width: 320; height: 480
      color: "lightgray"

      Text {
          id: helloText
          text: "Hello world!"
          y: 30
          anchors.horizontalCenter: page.horizontalCenter
          font.pointSize: 24; font.bold: true

          MouseArea { id: mouseArea; anchors.fill: parent }

          states: State {
              name: "down"; when: mouseArea.pressed == true
              PropertyChanges { target: helloText; y: 160; rotation: 180; color: "red" }
          }

          transitions: Transition {
              from: ""; to: "down"; reversible: true
              ParallelAnimation {
                  NumberAnimation { properties: "y,rotation"; duration: 500; easing.type: Easing.InOutQuad }
                  ColorAnimation { duration: 500 }
              }
          }
      }

      Grid {
          id: colorPicker
          x: 4; anchors.bottom: page.bottom; anchors.bottomMargin: 4
          rows: 2; columns: 3; spacing: 3

          Cell { cellColor: "red"; onClicked: helloText.color = cellColor }
          Cell { cellColor: "green"; onClicked: helloText.color = cellColor }
          Cell { cellColor: "blue"; onClicked: helloText.color = cellColor }
          Cell { cellColor: "yellow"; onClicked: helloText.color = cellColor }
          Cell { cellColor: "steelblue"; onClicked: helloText.color = cellColor }
          Cell { cellColor: "black"; onClicked: helloText.color = cellColor }
      }
  }

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<a name="walkthrough"></a>
<h2 id="walkthrough">Walkthrough</h2>
<pre class="qml">

          states: State {
              name: "down"; when: mouseArea.pressed == true
              PropertyChanges { target: helloText; y: 160; rotation: 180; color: "red" }
          }

</pre>
<p>First, we create a new <i>down</i> state for our text type. This state will be activated when the <a href="qml-qtquick-mousearea.html">MouseArea</a> is pressed, and deactivated when it is released.</p>
<p>The <i>down</i> state includes a set of property changes from our implicit <i>default state</i> (the items as they were initially defined in the QML). Specifically, we set the <code>y</code> property of the text to <code>160</code>, the rotation to <code>180</code> and the <code>color</code> to red.</p>
<pre class="qml">

          transitions: Transition {
              from: ""; to: "down"; reversible: true
              ParallelAnimation {
                  NumberAnimation { properties: "y,rotation"; duration: 500; easing.type: Easing.InOutQuad }
                  ColorAnimation { duration: 500 }
              }
          }

</pre>
<p>Because we don't want the text to appear at the bottom instantly but rather move smoothly, we add a transition between our two states.</p>
<p><code>from</code> and <code>to</code> define the states between which the transition will run. In this case, we want a transition from the default state to our <i>down</i> state.</p>
<p>Because we want the same transition to be run in reverse when changing back from the <i>down</i> state to the default state, we set <code>reversible</code> to <code>true</code>. This is equivalent to writing the two transitions separately.</p>
<p>The <a href="qml-qtquick-parallelanimation.html">ParallelAnimation</a> type makes sure that the two types of animations (number and color) start at the same time. We could also run them one after the other by using <a href="qml-qtquick-sequentialanimation.html">SequentialAnimation</a> instead.</p>
<p>For more details on states and transitions, see <a href="qtquick-statesanimations-states.html">Qt Quick States</a> and the states and transitions example.</p>
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