更改了 Qml 中 JavaScript 绑定的事件?

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，我总是得到最后一个选择的容器，而不是当前选择的容器：

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是为currentContainer提供另一个信号：onCurrentContainerChanged().

但是谁称之为特殊信号呢？

Answer 1

我可以使用C++辅助类来解决这个问题：

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)
};

用法非常简单：

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

我不确定这是否违反了任何Qml/QtQuick哲学，但它有效。