QML 属性绑定取决于同一组件中的其他绑定

Question

假设我有一个QtObject，它有一些属性。在同一个QtObject 中使用其他绑定中的绑定是否有任何缺点：

QtObject {
    // This is set by the caller
    property var myObject

    readonly property bool haveMyObject: myObject ? true :  false
    readonly property bool isSomething1: haveMyObject ? myObject.isSomething1 :  false
    readonly property bool isSomething2: haveMyObject ? myObject.isSomething2 :  false
    readonly property bool isSomething3: haveMyObject ? myObject.isSomething3 :  false
    readonly property bool isSomething4: haveMyObject ? myObject.isSomething4 :  false
    readonly property bool isSomething5: haveMyObject ? myObject.isSomething5 :  false
}

而不是这个：

QtObject {
    // This is set by the caller
    property var myObject

    readonly property bool haveMyObject: myObject ? true :  false
    readonly property bool isSomething1: myObject ? myObject.isSomething1 :  false
    readonly property bool isSomething2: myObject ? myObject.isSomething2 :  false
    readonly property bool isSomething3: myObject ? myObject.isSomething3 :  false
    readonly property bool isSomething4: myObject ? myObject.isSomething4 :  false
    readonly property bool isSomething5: myObject ? myObject.isSomething5 :  false
}

哪一个更可取？我问的原因是因为 Qt 文档的评估顺序是未定义的。

Answer 1

订单完全未定义是不正确的。绑定按其依赖关系定义的顺序进行评估。对于任何dependant-dependency 对，保证dependency 端在dependant 之前评估。因此，每个isSomething 属性都会在它的依赖项haveMyObject 被评估/更新之后进行评估/更新。