QML 与C++函数互相调用

QML函数可在C++中调用,反之亦然.

所有的QML函数都被暴漏在了元数据系统中,并可通过QMetaObject::invokeMethod()调用.C++应用程序调用QML函数:

// 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()的参数必须指定为QVariant类型,这是QML函数和返回值的通用数据类型.

在QML中调用C++函数,函数必须是Qt的槽或标记了Q_INVOKABLE宏的函数,才能在QML中访问.下面范例中,QML代码调用了(使用QDeclarativeContext::setContextProperty()设置到QML中的)myObject对象的方法:

 // 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支持调用C++的重载函数.如果C++中有多个同名不同参的函数,将根据参数数量和类型调用正确的函数