title: QFileDialog: GtkDialog mapped without a transient parent
body: <p>I've a source code snippet of a program written with Qt in C++, running under Linux, that creates a QFileDialog for opening an existing file. If I execute this, everything seems to work alright but when the dialog was created I got a warning saying <strong>"Gtk-Message: GtkDialog mapped without a transient parent"</strong>.</p>
  
  <p>In another <a href="https://stackoverflow.com/questions/29883211/gtkdialog-mapped-without-a-transient-parent">thread</a> I figured out that calling this function "gtk_window_set_transient_for()" fixes this error. But this function is part of the GTK library but I use the Qt framework. So are there any solutions to fix this error?</p>
  
  <p>Parent of this dialog is a QMainWindow:</p>
  
  <pre><code>QString filename = QFileDialog::getOpenFileName(this, "Open File");
  </code></pre>