以下代码为什么报错。难产没人知道吗？问了这么多次，好让我失望！(60分)

procedure MouseDown(Sender: TObject
Button: TMouseButton;
Shift: TShiftState
X, Y: Integer);
begin
if Button <> mbRight then
begin
ReleaseCapture;
(sender as tspeedbutton).Perform(WM_SysCommand, $f017, 0);
end;
end;

procedure Tjtplt1.SpeedButton1Click(Sender: TObject);
begin
(sender as tspeedbutton).OnMouseDown :=mousedown;{运行至此报错。incompatible types:"tobject" and "tmousedown"}
end;

加上
procedure Tjtplt1.MouseDown(Sender: TObject
Button: TMouseButton;
Shift: TShiftState
X, Y: Integer);

同意同上，再者最好不要用mousedown这个名字。

这样呢：
procedure TForm1.SpeedButton1Click(Sender: TObject);
begin
(sender as tspeedbutton).OnMouseDown :=Form1.FormMouseDown
end;
procedure TForm1.FormMouseDown(Sender: TObject
Button: TMouseButton;
Shift: TShiftState
X, Y: Integer);
begin
if Button <> mbRight then
begin
ReleaseCapture;
(sender as tspeedbutton).Perform(WM_SysCommand, $f017, 0);
end;
end;

多谢大家，给分。不知为何过程前没有"Tform1"............不可以，不加难道在本单元不可以引用吗。