Question

I’m changing the parent of a frame a runtime to move the frame from one form to another. That works fine but after that my components do not receive mouse events any longer. For example, CM_MOUSEENTER and CM_MOUSELEAVE is not fired.

Frame.Parent := SecondDisplayForm;
Frame.Align := alClient;
SecondDisplayForm.Show;

I don’t understand this effect and I don’t really know what information to provide, so if you have hints please help me out here.

Answer 1

It works in D7 as NGLN reported, but in BDS2006 it’s reproducible. I found that it’s important to change the parent after the cm_mouseenter, and before cm_mouseleave, otherways ther’s no problem. The problem is in the controls.pas I think, maybe it’s a bug. Playing around a little bit I found out that if you Perform a wm_mouseleave message before changing the parent everything is fine again.

In my sample code i change the parent in an onclick event.

  TFrame3 = class(TFrame)
    procedure FrameClick(Sender: TObject);
  private
    procedure CMMouseEnter( var msg: TMessage ); message CM_MOUSEENTER;
    procedure CMMouseLeave( var msg: TMessage ); message CM_MOUSELEAVE;
  public
  end;

implementation

procedure TFrame3.CMMouseEnter(var msg: TMessage);
begin
  inherited;
  Color := clRed;
end;

procedure TFrame3.CMMouseLeave(var msg: TMessage);
begin
  inherited;
  Color := clBlue;
end;

procedure TFrame3.FrameClick(Sender: TObject);
begin
if parent = Form1 then
  begin
    Perform( WM_MOUSELEAVE, 0, 0 );
    parent := Form2;
    align := alClient;
    Form1.Hide;
    Form2.Show;
  end else
  begin
    Perform( WM_MOUSELEAVE, 0, 0 );
    parent := Form1;
    align := alClient;
    Form2.Hide;
    Form1.Show;
  end;
end;

I think the problem is related to the FMouseControl in Controls.pas, but haven’t investigated it properly.