QML屬性綁定取決於同一組件中的其他綁定

Question

假設我有一個QtObject，它有一些屬性。有沒有用在其他在同一QtObject結合一個有約束力的任何缺點：

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 
} 

，而不是這樣的：

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 
} 

哪一個最好？我問的原因是因爲Qt文檔評估的順序是不確定的。

Answer 1

訂單完全未定義是不正確的。綁定以依賴關係定義的順序進行評估。對於任何dependant-dependency對，保證在dependant之前評估dependency方。因此，每isSomething財產被評估/更新後它依賴haveMyObject已被評估/更新。