title: redraw a custom uiview when changing a device orientation
body: <ol>
  <li>If I draw my chart inside <code>- (void)drawRect:(CGRect)rect</code> is just enough to set [<code>_chartView setContentMode:UIViewContentModeRedraw]</code> and this method will be called when device changes it's orienatation and it's possible to calculate f.e. new center point for my chart.</li>
  <li>If I create a view like a subview using <code>- (id)initWithFrame:(CGRect)frame</code> and then add it in view controller like <code>[self.view addSubview:chartView];</code>. How in this case I can handle rotation to redraw my chart?</li>
  </ol>