更改Qml中的JavaScript绑定事件？

Question

我有一个由JavaScript表达式（currentContainer）定义的属性：

Item { 
    id: theContainer 

    property alias currentIndex: theListView.currentIndex 
    signal onCurrentIndexChanged() 

    property MyCustomCppContainer currentContainer: { 
     if(theListView.currentIndex >= 0) 
      theModel.getCustomContainer(theListView.currentIndex) 
     else 
      null 
    } 
    signal onCurrentContainerChanged() // nobody calls this signal (yet) 

    MyCustomCppModel { 
     id: theModel 
    } 

    ListView { 
     id: theListView 

     anchors.fill: parent 

     model: theModel 
     currentIndex: -1 
     onCurrentIndexChanged: theContainer.onCurrentIndexChanged() 

     /* Other properties stripped for example */ 
    } 
} 

可悲的是我总是最后选定的容器，而不是当前所选择的一个：

ContainerItem { 
    onCurrentIndexChanged: { 
     //On first change, currentContainer is null 
     //though the first one was selected 

     //After selecting the second entry 
     //I get the result I expected last time 

     console.log(currentContainer.name); 
    } 
} 

我认为一个解决方案会有另一个信号currentContainer：onCurrentContainerChanged()。

但是谁称这个特殊信号？

Answer 1

我可以解决这个使用C++辅助类：

class PropertyChangedHelper : public QObject 
{ 
    Q_OBJECT 
    Q_PROPERTY(QVariant theProperty WRITE setTheProperty NOTIFY thePropertyChanged) 

public: 
    PropertyChangedHelper(QObject* parent = nullptr) : QObject(parent) {} 
    virtual ~PropertyChangedHelper() {} 

    void setTheProperty(QVariant) { 
     Q_EMIT thePropertyChanged(); 
    } 

Q_SIGNALS: 
    void thePropertyChanged(); 

private: 
    Q_DISABLE_COPY(PropertyChangedHelper) 
}; 

用法很简单：

PropertyChangedHelper { 
    theProperty: containerItem.currentContainer 
    onThePropertyChanged: { 
     console.log(containerItem.currentContainer.name); 
    } 
} 

我不知道这是否违反了任何设为Qml/QtQuick哲学，但它的作品。