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authorGeir Vattekar <geir.vattekar@nokia.com>2012-05-07 13:06:02 +0200
committerQt by Nokia <qt-info@nokia.com>2012-05-09 00:56:16 +0200
commit727180c98472d94ec393e8fb15bb0938ddacb2a0 (patch)
tree04426756896b1ec840f7f68bdcca8451bd09644c /src/quick/doc/src/behaviors-and-states.qdoc
parent0b1ab6ba5553ecd0ba485d0d4a1aead83482fb46 (diff)
Doc: Moving Qt Quick docs for new doc structure
-moved documentation from doc/src/qtquick2 doc/src/localstorage doc/src/particles to src/quick/doc/ -fixed qdocconf file -fixed snippets, images, and other qdoc errors related to the new directories -fixed links in the main Qt Quick page Change-Id: Ie3408c2624f623c17de07e5635d5c7284d02b973 Reviewed-by: Alan Alpert <alan.alpert@nokia.com>
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+/****************************************************************************
+**
+** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:FDL$
+** GNU Free Documentation License
+** Alternatively, this file may be used under the terms of the GNU Free
+** Documentation License version 1.3 as published by the Free Software
+** Foundation and appearing in the file included in the packaging of
+** this file.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms
+** and conditions contained in a signed written agreement between you
+** and Nokia.
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*!
+\page qtquick-behaviors-states.html tutorial
+\title Using QML Behaviors with States
+\brief animating property changes with behaviors
+
+\section1 Using Behaviors with States
+
+In some cases you may choose to use a Behavior to animate a property change caused by a state change. While this works well for some situations, in other situations it may lead to unexpected behavior.
+
+Here's an example that shows the problem:
+
+\qml
+import QtQuick 2.0
+
+Rectangle {
+ width: 400
+ height: 400
+
+ Rectangle {
+ id: coloredRect
+ width: 100
+ height: 100
+ anchors.centerIn: parent
+
+ color: "red"
+ Behavior on color {
+ ColorAnimation {}
+ }
+
+ MouseArea {
+ id: mouser
+ anchors.fill: parent
+ hoverEnabled: true
+ }
+
+ states: State {
+ name: "GreenState"
+ when: mouser.containsMouse
+
+ PropertyChanges {
+ target: coloredRect
+ color: "green"
+ }
+ }
+ }
+}
+\endqml
+
+Testing the example by quickly and repeatedly moving the mouse in to and out of the colored rectangle shows that the colored rectangle will settle into a green color over time, never returning to full red. This is not what we wanted! The
+problem occurs because we have used a Behavior to animate the change in color, and our state change is trigged by the mouse entering or exiting the MouseArea, which is easily interrupted.
+
+To state the problem more formally, using States and Behaviors together can cause unexpected behavior when:
+\list
+\li a Behavior is used to animate a property change, specifically when moving from an explicitly defined state back to the implicit base state; and
+\li this Behavior can be interrupted to (re-)enter an explicitly defined state.
+\endlist
+
+The problem occurs because of the way the base state is defined for QML: as the "snapshot" state of the application just prior to entering an explicitly defined state. In this case, if we are in the process of animating from green back
+to red, and interrupt the animation to return to "GreenState", the base state will include the color in its intermediate, mid-animation form.
+
+While future versions of QML should be able to handle this situation more gracefully, there are currently several ways to rework your application to avoid this problem.
+
+1. Use a transition to animate the change, rather than a Behavior.
+
+\qml
+import QtQuick 2.0
+
+Rectangle {
+ width: 400
+ height: 400
+
+ Rectangle {
+ id: coloredRect
+ width: 100
+ height: 100
+ anchors.centerIn: parent
+
+ color: "red"
+
+ MouseArea {
+ id: mouser
+ anchors.fill: parent
+ hoverEnabled: true
+ }
+
+ states: State {
+ name: "GreenState"
+ when: mouser.containsMouse
+
+ PropertyChanges {
+ target: coloredRect
+ color: "green"
+ }
+ }
+
+ transitions: Transition {
+ ColorAnimation {}
+ }
+ }
+}
+\endqml
+
+2. Use a conditional binding to change the property value, rather than a state
+
+\qml
+import QtQuick 2.0
+
+Rectangle {
+ width: 400
+ height: 400
+
+ Rectangle {
+ id: coloredRect
+ width: 100
+ height: 100
+ anchors.centerIn: parent
+
+ color: mouser.containsMouse ? "green" : "red"
+ Behavior on color {
+ ColorAnimation {}
+ }
+
+ MouseArea {
+ id: mouser
+ anchors.fill: parent
+ hoverEnabled: true
+ }
+ }
+}
+\endqml
+
+3. Use only explicitly defined states, rather than an implicit base state
+
+\qml
+import QtQuick 2.0
+
+Rectangle {
+ width: 400
+ height: 400
+
+ Rectangle {
+ id: coloredRect
+ width: 100
+ height: 100
+ anchors.centerIn: parent
+
+ Behavior on color {
+ ColorAnimation {}
+ }
+
+ MouseArea {
+ id: mouser
+ anchors.fill: parent
+ hoverEnabled: true
+ }
+
+ states: [
+ State {
+ name: "GreenState"
+ when: mouser.containsMouse
+
+ PropertyChanges {
+ target: coloredRect
+ color: "green"
+ }
+ },
+ State {
+ name: "RedState"
+ when: !mouser.containsMouse
+
+ PropertyChanges {
+ target: coloredRect
+ color: "red"
+ }
+ }]
+ }
+}
+\endqml
+
+*/