Calling Qt-Gui from native iOS Gui & Vice versa



  • I currently have a native iOS GUI and a Qt-GUI. I'm trying to switch from one to another.

    To be clear: When i click on a button on the native GUI i want the Qt-GUI to show up and vice versa.

    I already found out which libraries i have to add to be able to use the Qt-Stuff. I created a QApplication in the AppDelegate.mm file:

    - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions: (NSDictionary *) launchOptions {
        // receive int argc, and char** argv for the QApplication.
        _qApp = new QApplication(_argc, _argv);
    }
    

    Furthermore my Qt application looks (at the moment) like this:

    void createQtGUI() {
        QPushButton* btn = new QPushButton("Some Button");
        QLabel* lbl = new QLabel("QTGui");
        QVBoxLayout* layout = new QVBoxLayout();
        layout->addWidget(lbl);
        layout->addWidget(btn);
    
        QWidget* window = new QWidget();
        window->setLayout(layout);
        window->show();
    }
    

    I'm calling the createQtGUI method in my ViewController.mm when pressing a button in the native iOS GUI. The code runs without throwing any error, but:

    The Qt-GUI is not shown. The application still shows the native gui without switching to the Qt-GUI.

    Has anybody got any idea how to fix that?



  • I've finally found out what was missing:

    The Qt-Objects provide a method called winId(). This method returns a WId which actually is (on iOS) an UIView*.

    You have to add that UIView* as Subview to your main view.


    In order to achieve that I changed my createQtGUI method as follows:

    WId createQtGUI() {
        ... // nothing changed here (only at the end)
        window->show();
    
        return window->winId();
    }
    

    And In my ViewController.mm (where I call my method):

    - (IBAction)ButtonClicked:(id)sender {
        UIView* newView = (__bridge UIView*)reinterpret_cast<void*>(createQtGUI());
        [self.view addSubview:newView];
    }
    

    Note: The double cast (__bridge UIView*)reinterpret_cast<void*>(...) is necessary because you can't just cast from WId to UIView* in Objective-C++.


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