title: how to set QDialog width and height and allow automatic window placement
body: <p>Is there a way to just initialize a QDialog's width and height and not change the x and y coordinates without using a ui file? I just have a simple QDialog and want to set only the width and height, and have the x and y automatically set to the center of the parent, but when I try setGeometry, the inherited geometry's x and y are 0. How does the x and y get set when the dialog is created using a ui file?</p>
  
  <pre><code>class MyDialog : public QDialog
  {
      MyDialog::MyDialog(QWidget *parent) :
          QDialog(parent)
      {
          setGeometry(geometry().x(), geometry().y(), 200, 400);
      }
  }
  </code></pre>