Implementing parent change animation with QML

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This code snippet shows how to implement an animation when the QML element's parent changes.

Article Metadata

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Tested with

Devices(s): Nokia 900

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Compatibility

Platform(s): S60 5th Edition
Maemo

Dependencies: Qt 4.7 and later

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Article

Keywords: QML, ParentChange, ParentAnimation

Created: kratsan (22 Jun 2010)

Last edited: hamishwillee (18 Oct 2012)

Overview

In the following code snippet there are two QML files. The file ui.qml contains the main view which places six differently coloured rectangles in the 3 x 2 QML Grid element. MyRect.qml contains the implementation of our self-made rectangle which will scale to full screen when clicked. At the same time its parent is changed.

The code snippet is meant to be run with qmlviewer.

Preconditions

• Qt 4.7 or higher is installed on your platform.

Source

ui.qml

import Qt 4.7
 
Rectangle {
    id: view
 
    width: 800; height: 480
    color: "black"
 
    Grid {
        id: grid
 
        property int itemWidth: grid.width / grid.columns
        property int itemHeight: grid.height / grid.rows
 
        anchors.centerIn: parent
        width: parent.width * 0.75; height: parent.height * 0.75
        spacing: 10; columns: 3; rows: 2
 
        MyRect { 
            width: grid.itemWidth
            height: grid.itemHeight
            color: "red"
        }
 
        MyRect {
            width: grid.itemWidth
            height: grid.itemHeight
            color: "green"
        }
 
        MyRect {
            width: grid.itemWidth
            height: grid.itemHeight
            color: "blue"
        }
 
        MyRect {
            width: grid.itemWidth
            height: grid.itemHeight
            color: "yellow"
        }
 
        MyRect {
            width: grid.itemWidth
            height: grid.itemHeight
            color: "brown"
        }
 
        MyRect {
            width: grid.itemWidth
            height: grid.itemHeight
            color: "gray"
        }
    }
}

MyRect.qml

When MouseArea is clicked, the state maximized is entered. This is triggered by the rect.maximized property. Transition will animate the change of parent by using ParentAnimation.

The z-order of container is changed between the states in order to prevent the rectangle from going behind other rectangles when coming back from the maximized state to the default state.

Because we are using the QML Grid to position the MyRects in the scene, we want to have an invisible Item to be left in the grid when the rect is re-parented to the view. Without the Item, the grid would rearrange its children when MyRect is re-parented to the view. This behavior is not desired here.

import Qt 4.7
 
Item {
    id: container
 
    property alias color: rect.color
 
    Rectangle {
        id: rect
 
        property bool maximized: false
 
        width: parent.width; height: parent.height; radius: 10
 
        MouseArea { anchors.fill: parent; onClicked: rect.maximized = !rect.maximized }
 
        states: State {
            name: "maximized"
            when: rect.maximized
            ParentChange {
                target: rect
                parent: view
                x: 0; y: 0
                width: parent.width; height: parent.height
            }
            PropertyChanges { target: rect; radius: 0; z: 1 }
            PropertyChanges { target: container; z: 1 }
        }
 
        transitions: Transition {
            from: "*"
            to: "maximized"
            reversible: true    // reverses the animation when going back to default state
            ParentAnimation {
                target: rect
                SequentialAnimation {
                    PropertyAction { target: container; property: "z" }
                    PropertyAnimation {
                        target: rect
                        properties: "x,y,width,height,radius"
                        easing.type: "InOutQuart"; duration: 1000
                    }
                }
            }
        }
    }
}

Postconditions

The snippet demonstrated using ParentChange and ParentAnimation QML elements to implement a smooth animation of a self-made rectangle to full screen when the rectangle was clicked. Also, the animation was reversed when the maximised rectangle was clicked again.