How to Retrieve the Viewable Area of a Window or Control

Environment: Visual Studio .NET / C#

How to Retrieve the Viewable (Client) Area of a Window or Control

The ClientRectangle Property doesnt always give you a true viewable area of a window. For example, this occurs when the window is an MDI child window or child window of an MDI child window because the MDI parent may not be large enough to display all of the MDI child.

To get the viewable area, you need to call a Win32 function named GetClipBox(). Following is a function that calls GetClipBox() and converts the results to something that .NET can use.

public static Rectangle GetViewableRect( Control control )
{
  //! Get a graphic from the control; we need the HDC.
  Graphics graphics = Graphics.FromHwnd(control.Handle);

  //! Get the hDC. (Remember to call ReleaseHdc() 
  //  when finished.)
  IntPtr hDC = graphics.GetHdc();

  //! Create a rectangle to receive the viewable 
  //  area of the control.
  WIN32Rect r = new WIN32Rect();

  //! Call the Win32 method that receives the viewable area.
  GetClipBox(hDC, ref r);

  //! Convert that to a .NET rectangle.
  Rectangle rectangle = new Rectangle( r.left, 
                                       r.top,
                                       r.right - r.left,
                                       r.bottom - r.top );

  //! Release the HDC. (If you don't, the CLR throws an 
  //  exception when it tries to Finalize/Dispose it.)

  graphics.ReleaseHdc(hDC);

  //! Dispose of the graphic; we don't need it any more.
  graphics.Dispose();
  graphics = null;

  return rectangle;
}

Downloads

Download demo project -- 11.13 KB