title: How to set enable resize the main window again after setFixedSize
body: <p>In my code I set the fixed size for the main window If I open .mp3 file, now I need to resize the main window if I open another file format. how to enable resize if I open any other file format.I tried this: <code>this-&gt;setFixedSize(this-&gt;sizeHint());</code> but not working </p>
  
  <p>this is my code.</p>
  
  <pre><code>void MainWindow::on_actionOpen_triggered()
  {
    QString filename= QFileDialog::getOpenFileName(this,"Open Folder","","Open a File(*.*)");
    on_actionStop_triggered();
     player-&gt;setMedia(QUrl::fromLocalFile(filename));
     on_actionPlay_triggered();
  
      if(filename.endsWith(".mp3")){
          qDebug() &lt;&lt; " file is mp3";
          this-&gt;setFixedSize(648,425);
  
      }else{
          this-&gt;setFixedSize(this-&gt;sizeHint()); //this not working. 
      }
  }
  </code></pre>