QML函式可在C++中呼叫,反之亦然.

所有的QML函式都被暴漏在了元資料系統中,並可通過QMetaObject::invokeMethod()呼叫.C++應用程式呼叫QML函式:

// MyItem.qml
 import QtQuick 1.0

 Item {
     function myQmlFunction(msg) {
         console.log("Got message:", msg)
         return "some return value"
     }
 }



 // main.cpp  
 QDeclarativeEngine engine;  
 QDeclarativeComponent component(&engine, "MyItem.qml"
 
);  
 QObject *object = component.create();  

 QVariant returnedValue;  
 QVariant msg = "Hello from C++";  
 QMetaObject::invokeMethod(object, "myQmlFunction",  
         Q_RETURN_ARG(QVariant, returnedValue),  
         Q_ARG(QVariant, msg));  

 qDebug() << "QML function returned:" << returnedValue.toString();   
 

注意QMetaObject::invokeMethod()中Q_RETURN_ARG() 和Q_ARG()的引數必須指定為QVariant型別,這是QML函式和返回值的通用資料型別.

在QML中呼叫C++函式,函式必須是Qt的槽或標記了Q_INVOKABLE巨集的函式,才能在QML中訪問.下面範例中,QML程式碼呼叫了(使用QDeclarativeContext::setContextProperty()設定到QML中的)myObject物件的方法:

 // MyItem.qml
 import QtQuick 1.0

 Item {
     width: 100; height: 100

     MouseArea {
         anchors.fill: parent
         onClicked: {
             myObject.cppMethod("Hello from QML"
 
)
             myObject.cppSlot(12345)
         }
     }
 }


//main.cpp
 class MyClass : public QObject  
 {  
     Q_OBJECT  
 public:  
     Q_INVOKABLE void cppMethod(const QString &msg) {  
         qDebug() << "Called the C++ method with" << msg;  
     }  

 public slots:  
     void cppSlot(int number) {  
         qDebug() << "Called the C++ slot with" << number;  
     }  
 };  

 int main(int argc, char *argv[]) {  
     QApplication app(argc, argv);  

     QDeclarativeView view;  
     MyClass myClass;  
     view.rootContext()->setContextProperty("myObject", &myClass);  

     view.setSource(QUrl::fromLocalFile("MyItem.qml"));  
     view.show();  

     return app.exec();  
 }  

QML支援呼叫C++的過載函式.如果C++中有多個同名不同參的函式,將根據引數數量和型別呼叫正確的函式