How to know when my control changes size?

Question

I'm building a custom control, and I need it to be able to respond when it gets resized. I need the old dimensions and the new dimensions available in order to do some calculations.

Unfortunately, the SetWidth and SetHeight methods are private to TControl, not protected, and so I can't override them. Is there any other way to know that my control's about to be resized, and to have the old size and the new size both available?

Answer 1

Override the SetBounds public method. It passes in the new size, and you can use the Width and Height properties to get the current width/height.

procedure SetBounds(ALeft, ATop, AWidth, AHeight: Integer); override;

Answer 2

An alternative solution, would simply be to use the OnResize event of TControl. This is not necessarily published in some controls but if it isnt you can still attach a handler in code.

MyControl.OnResize := MyResizeEvent;

Although this will only allow you to get the new size, if you have kept the oldsize in a set of variables then you can do what you wish.

function Myform.MyResizeEvent(Sender: TObject) ;
var

begin

  DoSomethingOnResize(OldHeight, OldWidth, (Sender as TControl).Height,(Sender as TControl).Width);
  OldHeight := (Sender as TControl).Height;
  OldWidth := (Sender as TControl).Width;

end;