How to catch the moment when the parent control has been resized?

Question

I have a visual component derived from TWinControl. I need to do some work in my component when its parent control has been resized. In general case, the \"Align\" property

Answer 1

I was looking for a solution to a similar problem. But in my case I cannot have such restrictions on alignment, and subclassing seemed overkill (the alignment thingie looks overkill too, now that I look at it)

So I came up with the following idea:

type
  TMyComponent = class(TControl)
  private
    FParentLastWidth: integer;
  ...
    procedure Invalidate; override;
  ...
  end;

procedure TMyComponent.Invalidate;
begin
  if (Parent <> nil) and (FParentLastWidth <> Parent.Width) then
  begin
    FParentLastWidth := Parent.Width;
    // do whatever when the parent resizes
  end;
  inherited;
end;

Add or replace the FParentLastWidth with whatever size you are tracking (I only needed reaction when the parent width changed. You can take it as an optimization so to not react to all kinds of changes which makes no difference for your component)