Qt 5.4/QML:如何正确地实现一个自定义c++类作为一个全局QML单例实例并实现其信号的代码(在QML中)?

I have a little C++ class that I want to register with QML so I can access it from QML code and provide a safe API for the QML developer - while keeping the complex stuff "under the hood" and hidden from the perspective of QML.I have a little C++ class that I want to regist