CODEWITHSUNDEEP
c++qtqmainwindow
Tarandeep Gill
Tarandeep Gill

Reputation: 1536

QMainWindow opens from main() function, but not from any other function

I am having a weird problem with my Qt app. I have a QMainWindow, conveniently MainWindow.

The following code works from the main() function:

int main(int argc, char *argv[])

{
    ..
    MainWindow mainWindow;
    mainWindow.show();
    ..
}

But, with the following does not show the MainWindow at all:

int main(int argc, char *argv[])
{
    AnotherClass::staticFunction();
}


class AnotherClass: public QObject {
Q_OBJECT
public:
    static void staticFunction();
}

void AnotherClass::staticFunction() {
    MainWindow mainWindow;
    mainWindow.show();
    return ;
}

Upvotes: 1

Views: 499

Answers (2)

Claudio
Claudio

Reputation: 1706

In this code

void AnotherClass::staticFunction() {
    MainWindow mainWindow;
    mainWindow.show();
    return ;
}

The instance mainWindow will go out of scope after the closing }, and then destroyed. You will have to allocate it on the heap using new to have it outlive staticFunction().

void AnotherClass::staticFunction() {
    MainWindow * mainWindow = new MainWindow;
    mainWindow->show();
    return ;
}

You will also need to somehow keep track of the pointer and having it deleted later (perhaps using a smart pointer).

And of course you will have to have a QApplication and call exec() on it in order to start the main event loop.

Upvotes: 1

Tarandeep Gill
Tarandeep Gill

Reputation: 1536

Oh my bad! Its because main never returns and enters the exec loop. However, since my function was returning immediately, the window was getting destroyed. Changing MainWindow mainWindow; to MainWindow* mainWindow = new MainWindow(); solved my problem:

Upvotes: 2

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