How to create a QInputDialog in a new thread?

Question

Basically I'm calling a function from another thread using QtConcurrent .

Working as expected but once I create a QInputDialog within the called function, I'm getting an assertion exception telling me that I have to create the Dialog in the Main GUI Thread.

To be more specific this line:

password = QInputDialog::getText( this , tr( "Password" ) , tr( "Enter Password:" ) , QLineEdit::Password , selectedPassword , &ok );

Now the question would be how can I call the Dialog from a new thread without too much extra work.

Answer 1

You can't create widgets outside from main thread. You can emit signal from network thread and create dialog in main thread.

Or do something like this (pseudo-code):

class NotificationManager : public QObject
{
  Q_OBJECT
//...
public slots:
  void showMessage( const QString& text )
  {
    if ( QThread::currendThread() != this->thread() )
    {
      QMetaObject::invoke( this, "showMessage", Qt::QueuedConnection, Q_ARG( QString, text );
      // Or use Qt::BlockingQueuedConnection to freeze caller thread, until dialog will be closed
      return;
    }
    QMessageBox::information( nullptr, QString(), text );
  }
};

class ThreadedWorker : public QRunnable
{
  ThreadedWorker( NotificationManager *notifications )
    : _notifications( notifications )
  {}

  void run() override
  {
    // Do some work;
    notifications->showMessage( "Show this in GUI thread" );
  }

private:
  NotificationManager *_notifications;
}