Using QtQuick / QML Passively with C++

Question

Veteran C++ and C#/WinForms programmer here, getting familiar with Qt/QML.

There's a lot of information on how to call into C++ from QML, and I've got that working just fine, but I'd rather treat QML passively and manipulate it from C++ when at all possible.

For example:

frmLogin::frmLogin()
{
    // Load QML file

    // Wire up controls to their own pointers
    cmdOK = QtQuick_GetControlFromQML("cmdOK");
    cmdQuit = QtQuick_GetControlFromQML("cmdQuit");
}

void frmLogin::Show()
{
    MyQMLPointerToWindow->Show();
}

void frmLogin::DoSomethingFromCPP()
{
    cmdOK->SetProperty("text", "I just changed the button text");
    rectBox->SetProperty("visible", true); // rectBox Rectangle from QML now appears on the screen

    frmMainMenu = new frmMainMenu(); // Create new main menu window
    frmMainMenu->ShowDialog(); // modal display
}

Is there a way to do this? Is it highly discouraged? I'm trying to make a multi-form modal application. It's difficult to find straightforward answers on all of this because it seems like QtQuick has gone through several design iterations. Any advice is appreciated!

Why are you using QML at all if you want to do everything in C++? — Deadron
Because I want to use Qt Quick GUI system, not traditional Qt. — user1054922

Mitch Mitch · Accepted Answer · 2014-08-07T16:52:31

If you know the objectName of the item you're interested in, you can use QObject::findChild():

QQuickItem *okButton = findChild<QQuickItem*>("cmdOK");

If the button is declared as a property in QML:

Item {
    id: item

    property alias button: item.button

    Button {
        id: button
        text: "OK"
    }
}

Then you can access it as a property in C++:

QObject *button = property("button").value<QObject*>();
button->setProperty("text", "I just changed the button text");

Using QtQuick / QML Passively with C++

1 Answers