Emit signal from C++ to QML without any parameters

[bwylegly]

Hi.

Im trying to implement logging mechanism into my app.

What I've done so far is created LoginView.qml file:

// LoginView.qml

Item {

    id: loginView
    signal loginClicked(string textField_usr, string textField_pwd);

    objectName: "loginView"
// ATTEMPTS SO FAR
//   Connections {
//       target: MasterController.ui_loginController
//       onLoginSuccessful: MasterView.contentFrame.replace("qrc:/views/DashboardView.qml")
//        onLoginFailed: console.log("login failed")
//    }

//            LoginController {
//                id: loginController
//                onLoginSuccessful: MasterView.contentFrame.replace("qrc:/views/DashboardView.qml")
//                onLoginFailed: console.log("login failed")
//            }

    GroupBox {
       /* Some styling, including  TextFields etc*/

        Button {
            id: button
            objectName: "proceed_button"
        
            /*more styling*/

            onClicked: {
                loginClicked(username_textField.text, password_textInput.text)
            }
        }
    }
}

LoginView.qml gets loaded by MasterView.qml onCompleted()

Window {
    /*Some stuff - nothing related to login process*/

   StackView{
        id: contentFrame
        /*...*/

        initialItem: Qt.resolvedUrl("qrc:/views/SplashView.qml")
    }


    Component.onCompleted: {
       contentFrame.replace("qrc:/views/LoginView.qml")

    }
}

With that in place, I have created LoginViewController class:

namespace cms{
namespace controllers{

class CMSLIBSHARED_EXPORT LoginViewController : public QObject{
    Q_OBJECT

private:

    QObject* loginButton {nullptr};

public:


    explicit LoginViewController(QObject* _parent = nullptr) : QObject(_parent) {}

    LoginViewController(QQmlApplicationEngine* engine){
        QObject* loginView = engine->rootObjects().first()->findChild<QObject*>("loginView");
    
        loginButton = loginView->findChild<QObject*>("proceed_button");

        QObject::connect(loginView, SIGNAL(loginClicked(QString, QString)), this, SLOT(loginButtonClicked(QString, QString)));

    }


public slots:
    void loginButtonClicked(QString user, QString pwd);

signals:
    void loginSuccessful();
    void loginFailed();
};

}
}

LoginViewController is a member of MasterController, which I export as MasterController's Q_PROPERTY:

Q_OBJECT
Q_PROPERTY(cms::controllers::LoginViewController* ui_loginController READ loginController CONSTANT)

public:
LoginViewController* loginController();

Here's a part that im not really sure of.
I registered my LoginViewController class as QML type inside main.cpp

qmlRegisterType<cms::controllers::MasterController>("CMS", 1, 0, "MasterController");

//newly added
qmlRegisterType<cms::controllers::LoginViewController>("CMS", 1, 0, "LoginController");

Everything works fine when I emit the signal from Qml into C++, login function works as intended, but I am getting stucked when i try to emit different signals depending on login method output.

After signal from Qml button gets emitted, it triggers login function

void LoginViewController::loginButtonClicked(QString user, QString pwd)
{
        std::cerr << "loginButtonClicked " << std::endl;
        if(cms::administration::Clinic::login(user.toStdString(), pwd.toStdString())){
            loginSuccessful(); return;
        }
        loginFailed();
}

As you can see, here I'd like to emit signal into QML. I came by different posts, different documentation pages, and i feel like left with too many tools to work with.

Could somebody guide me, on how should I emit and handle the signal inside QML?
Moreover, if there's any "better" or more suitable solution for this mechanism, I'd be happy to hear about it.

Best regards!

[Charby]

I would do the following :

• instead of registering your LoginViewController, I would simply create a context property for your controller instance. Something like :

cms::controllers::LoginViewController controler;
QQmlApplicationEngine engine;
engine->rootContext()->setContextProperty("loginCtrl", this);

• instead of retrieving the login button from c++ and create the connection etc...simply call loginButtonClicked on the controller property in the button onClicked handler.

Button {
            id: button
            objectName: "proceed_button"
        
            /*more styling*/

            onClicked: loginCtrl.loginButtonClicked(username_textField.text, password_textInput.text)
        }

• use a "Connection" item in QML with the controller property as target to react to loginSuccess/loginFailure

Connection{
   target: loginCtrl
   onLoginSuccessful: {}
   onLoginFailed:{}
}

[bwylegly]

Hi @Charby, thanks for your feedback.
Your idea works just fine, but im getting those errors, which I cannot get rid of.

I have added Connection item you have mentioned about:

• inside LoginView.qml

Connections {
        target: loginController
        onLoginSuccessful : { masterView.contentFrame.replace("qrc:/views/DashboardView.qml") }
        onLoginFailed: {console.log("Failed") }
    }

• inside main.cpp

    cms::controllers::MasterController masterController;

    QQmlApplicationEngine engine;
    engine.addImportPath("qrc:/");

    engine.rootContext()->setContextProperty("masterController", &masterController);

    engine.load(QUrl(QStringLiteral("qrc:/views/MasterView.qml")));

    cms::controllers::LoginViewController lvc(&engine);
    engine.rootContext()->setContextProperty("loginController", &lvc);

But it produces following errors:

qrc:/views/LoginView.qml:13:5: QML Connections: Cannot assign to non-existent property "onLoginFailed"
qrc:/views/LoginView.qml:13:5: QML Connections: Cannot assign to non-existent property "onLoginSuccessful"
qrc:/views/LoginView.qml:14: ReferenceError: loginController is not defined

Any ideas?

[Charby]

lvc needs to be defined as a context property before the qml engine call of load