如何从 QML 连接 C++ 对象的破坏信号?

2022-01-19 00:00:00 qt qtquick2 qml javascript

我想从 QML 连接 C++ QObject 的破坏信号，所以我这样做了:

I want to connect a destroyed signal of C++ QObject from QML so I did this:

Rectangle
{
    id: root
    width: 128
    height: 128

Button
{
    anchors.centerIn: parent
    text: "Click me"
    onClicked:
    {
        qobj.Component.onDestruction.connect(function(){console.log("It destroy")}) // qobj is set from c++
        qobj.destroy() // should output "It destroy"
    }
}

但是当我销毁 qobj 时没有打印任何内容.

But nothing is printed when I destroy qobj.

推荐答案

在一般情况下，您可以使用 连接 元素:

In the general case, you can connect to signals emitted from a C++ object using a Connections element:

Connections {
    target: yourObjectComingFromCpp
    onSomeSignal: console.log("Something")
}

或者在 Javascript 中通过在 JS 映射对象的相应属性上调用 connect 函数:

or in Javascript by calling the connect function on the corresponding property of the JS-mapped object:

// without the *on*!
yourObjectComingFromCpp.someSignal.connect( /* JS function here */ );

<小时>

但是:这不适用于特定的 QObject::destroyed 信号，这些信号被强制列入黑名单并且在 QML 中永远不可用(来源).

However: this doesn't work for the specific QObject::destroyed signals, which are forcibly blacklisted and never available in QML (source).

我猜原因是该对象无论如何都从 QML 上下文中消失了，而且当发出该信号时，您将深入到 QObject 自己的析构函数中，这意味着您的子类上的任何属性或方法访问在那一点.

I guess the reason is that the object is gone from the QML context anyhow at that point, plus when that signal is emitted you're deep into QObject's own destructor, which means any property or method access on your subclass is invalid at that point.

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