I have multiple qml Files that get pushed via StackView. How do I connect them to C++

问题

My Projects contains 6 qml Files: The main.qml opens a new ApplicationWindow and declares the toolbar. It also initalizes StackView with the initalItem homescreen.qml. On the Home Screen I have different buttons which open different qml Files, via stack.push("URL"). Besides the main.qml all Files start with Item{}. I've been able to connect signals from the main.qml and the home.qml. But I've been unable to access Objects that are deeper in the stack. I don't know if I hvae to change my .cpp code to access the other objects, or if I should change the Initalization of StackView, so that all Files are loaded and accessible at the beginning. Here is the code, broke down to the very basics:

main.qml

ApplicationWindow {
      Rectangle{
                id: homeButton
                objectName: "homeButton"
                signal qmlSignal(string msg)
                MouseArea {
                     onClicked:  {stack.push({item:"qrc:/home.qml}); homeButton.qmlSignal("Hello")}
                }
      }
      StackView{
           initalItem: "qrc:/home.qml"
      }

}

secondframe.qml // A randomw qml File that comes after the Home Screen

Item {
      Rectangle{
                id: test
                objectName: "test"
                signal qmlSignal(string msg)
                MouseArea {
                     onClicked:  {stack.push({item:"qrc:/thirdframe.qml}); test.qmlSignal("Hello")}
                }
      }
}

main.cpp

QApplication app (argc, argv);
QQmlEngine enigne;
QQmlComponent component(&engine, QUrl(QStringLiteral("qrl:/main.qml")));
QObject *object = componet.create();
QQmlComponent newcomponent(&engine, QUrl(QStringLiteral("qrl:/secondframe.qml")));
QObject *newobject = newcomponet.create();

MyClass myClass
QObject *home = object->findChild<QObject*>("homeButton");    // I'm able to connect to every Object in the main.qml or home.qml
QObject::connect(home,SIGNAL(qmlSignal(Qstring)), &myClass, SLOT(cppSlot(QString)));
QObject *test = newobject->findChild<QObject*>("test");       // Can't connect to the Objects in secondframe.qml
QObject::connect(test,SIGNAL(qmlSignal(Qstring)), &myClass, SLOT(cppSlot(QString)));

回答1:

A way better approach than to reach into the QML tree and pull out objects that might or might not be there is to provide C++ based API to QML.

Create a QObject based class that has the methods QML needs to be able to call as slots or Q_INVOKABLE

class MyAPI : public QObject
{
    Q_OBJECT
public slots:
    void cppSlot(const QString &text);
};

Create an instance of that and expose it to QML

MyAPI myApi;
QQmlEngine engine;
engine.rootContext()->setContextProperty("_cppApi", &myApi);

Use in QML as if "_cppApi" is an object id

MouseArea {
     onClicked:  {stack.push({item:"qrc:/thirdframe.qml}); _cppApi.cppSlot("Hello")}
}

回答2:

After pushing qmls on the stack, objects will be accessible. So when you emit some signal, when object will be on the stack, solution can look like this:

MyClass myClass
QObject *home = object->findChild<QObject*>("homeButton");    // I'm able to connect to every Object in the main.qml or home.qml
QObject::connect(home,SIGNAL(qmlSignal(Qstring)), &myClass, SLOT(cppSlot(QString)));

connect( myClass, MyClass::emitWhenQMLIsAlreadyOnTheStack, this, [this](){
    QObject *test = newobject->findChild<QObject*>("test");       // Now you should be able to connect
    QObject::connect(test,SIGNAL(qmlSignal(Qstring)), &myClass, SLOT(cppSlot(QString));
});

来源：https://stackoverflow.com/questions/41847939/i-have-multiple-qml-files-that-get-pushed-via-stackview-how-do-i-connect-them-t

标签

c++

qml

interaction

stackview