PropertyChanges

Describes new property bindings or values for a state. More...

Import Statement: import QtQuick

List of all members, including inherited members

Properties

explicit : bool
restoreEntryValues : bool
target : QtObject

Detailed Description

PropertyChanges is used to define the property values or bindings in a State. This enables an item's property values to be changed when it changes between states.

To create a PropertyChanges object, bind to properties of the target item like you would bind to local properties. This way you can define the new property values or bindings. For example:

import QtQuick 2.0

Item {
    id: container
    width: 300; height: 300

    Rectangle {
        id: rect
        width: 100; height: 100
        color: "red"

        MouseArea {
           id: mouseArea
           anchors.fill: parent
        }

        states: State {
           name: "resized"; when: mouseArea.pressed
           PropertyChanges {
               rect {
                   color: "blue"
                   height: container.height
               }
           }
        }
    }
}

When the mouse is pressed, the Rectangle changes to the resized state. In this state, the PropertyChanges object sets the rectangle's color to blue and the height value to that of container.height.

Note this automatically binds rect.height to container.height in the resized state. If a property binding should not be established, and the height should just be set to the value of container.height at the time of the state change, set the explicit property to true.

A PropertyChanges object can also override the default signal handler for an object to implement a signal handler specific to the new state:

PropertyChanges {
    myMouseArea.onClicked: doSomethingDifferent()
}

Note: PropertyChanges can be used to change anchor margins, but not other anchor values; use AnchorChanges for this instead. Similarly, to change an Item's parent value, use ParentChange instead.

Resetting Property Values

The undefined value can be used to reset the property value for a state. In the following example, when myText changes to the widerText state, its width property is reset, giving the text its natural width and displaying the whole string on a single line.

Rectangle {
    width: 300; height: 200

    Text {
        id: myText
        width: 50
        wrapMode: Text.WordWrap
        text: "a text string that is longer than 50 pixels"

        states: State {
            name: "widerText"
            PropertyChanges { myText.width: undefined }
        }
    }

    MouseArea {
        anchors.fill: parent
        onClicked: myText.state = "widerText"
    }
}

Immediate Property Changes in Transitions

When Transitions are used to animate state changes, they animate properties from their values in the current state to those defined in the new state (as defined by PropertyChanges objects). However, it is sometimes desirable to set a property value immediately during a Transition, without animation; in these cases, the PropertyAction type can be used to force an immediate property change.

See the PropertyAction documentation for more details.

Note: The visible and enabled properties of Item do not behave exactly the same as other properties in PropertyChanges. Since these properties can be changed implicitly through their parent's state, they should be set explicitly in all PropertyChanges. An item will still not be enabled/visible if one of its parents is not enabled or visible.

Note: For backwards compatibility with Qt 5, you can also specify PropertyChanges using the target property and plain property names without IDs. For example: PropertyChanges { target: myItem; x: 15 }. The form with ID instead of target is recommended. You may also need to use the form with target if the file is to be edited with Qt Design Studio. Mind that Qt Design Studio also imposes a number of further restrictions on the files it can work with.

See also States example, Qt Quick States, and Qt QML.

Property Documentation

explicit : bool

If explicit is set to true, any potential bindings will be interpreted as once-off assignments that occur when the state is entered.

In the following example, the addition of explicit prevents myItem.width from being bound to parent.width. Instead, it is assigned the value of parent.width at the time of the state change.

PropertyChanges {
    target: myItem
    explicit: true
    width: parent.width
}

By default, explicit is false.

restoreEntryValues : bool

This property holds whether the previous values should be restored when leaving the state.

The default value is true. Setting this value to false creates a temporary state that has permanent effects on property values.

target : QtObject

This property holds the object which contains the properties to be changed.

Note: You generally don't have to use this property. It only exists for compatibility with Qt 5 and for compatibility with Qt Design Studio.