Question

I have a Qt main window that will pop up a dialog box that has an OK and Cancel button. This dialog has a simple spinner that asks a user for a number that should be returned to the main window when OK or Cancel is pressed (for cancel, it will just send back -1).

I thought about using code in a signal in mainWindow.cpp like so:

void mainWindow::slot_openNumberDlg(){
    // Create a new dialog
    numberDlg dlg( this );

    // Show it and wait for Ok or Cancel
    if( dlg.exec() == QDialog::Accepted ){
        return;
    }
}

But how would I return the value of the spinner in the dialog back to main window if it is destroyed when the button is pressed?

I also thought about an alternative solution where I would initialize the dialog in mainWindow’s constructor, but it isn’t shown until a signal activated a slot in mainWindow.cpp like so:

// Create as pointer in main.h:
numberDlg *dlg;

// Initialize pointer and setup listener in constructor (main.cpp):
mainWindow::mainWindow(){
    dlg = new numberDlg();
    QObject::connect( dlg, SIGNAL( sig_retVal(int) ), ui->widget, SLOT( slot_showNum(int) ) );
}

// Make a function to handle show/close:
void mainWindow::slot_numberOpenClose(bool trigger){
    if(trigger){
        dlg->show();
    } else {
    dlg->close();
    }
}

The above code would be able to send the number from the dialog’s spinner to mainWindow using a signal/slot, but it won’t lock out mainWindow. I do not want the user to continue using mainWindow until the dialog has been accepted or rejected.

Any ideas on how I can lock the main window and send a number back to main on dialog close?

Answer 1

What you should do is create a function in your dialog class that returns the value you want, and use it like so from your main window:

void mainWindow::slot_openNumberDlg(){
    // Create a new dialog
    numberDlg dlg( this );

    // Show it and wait for Ok or Cancel
    if( dlg.exec() == QDialog::Accepted ){
        m_theValue = dlg.myValue(); // <--
        return;
    }
} // dlg goes out of scope

dlg won’t be destroyed until it goes out of scope where I placed the comment, so your method will work fine.