PropertyChanges QML Element

The PropertyChanges element describes new property bindings or values for a state. 更多...

Since:

Qt 4.7

所有成员列表，包括继承成员

特性

explicit : bool
restoreEntryValues : bool
target : Object

详细描述

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 .

要创建 PropertyChanges object, specify the target item whose properties are to be modified, and define the new property values or bindings. For example:

import QtQuick 1.0
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 { target: 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 在 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 特性到 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 {
    target: myMouseArea
    onClicked: doSomethingDifferent()
}

注意： 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 ParentChanges instead.

Resetting property values

The undefined value can be used to reset the property value for a state. In the following example, when theText 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 { target: myText; width: undefined }
        }
    }
    MouseArea {
        anchors.fill: parent
        onClicked: myText.state = "widerText"
    }
}

Immediate property changes in transitions

当过渡 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 element can be used to force an immediate property change.

见 PropertyAction 文档编制了解更多细节。

另请参阅 states example , States, and QtDeclarative .

特性文档编制

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.

默认值为 true . Setting this value to false creates a temporary state that has permanent effects on property values.

target : 对象

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