动态移动form上任意控件 (100分)

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls, ComCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Label1: TLabel;
    Memo1: TMemo;
    procedure Button1MouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure Button1MouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure Button1MouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Integer);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    MouseDownSpot:tpoint;
    capturing:bool;
  end;

var
  Form1: TForm1;
  c:tcontrol;
implementation

{$R *.dfm}

procedure TForm1.Button1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
  var
  a:tpoint;
begin
 if ssctrl in shift then begin
 a.X :=x;
 a.Y :=y;
 setcapture(windowfrompoint(a));
 [b][red]c:= form1.controlatpos(a,true,true);[/red][/b]
//这里 true,false都一样的结果
 capturing:=true;
 MouseDownspot.X :=x;
 mousedownspot.Y :=y;
 end;
end;

procedure TForm1.Button1MouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
 if capturing then
begin
 releasecapture;
 capturing:=false;
 c.Left :=c.Left-(mousedownspot.X-x);
 c.top :=c.top -(mousedownspot.y-y);
 end;
end;

procedure TForm1.Button1MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
if capturing=true then
begin
 c.Left :=c.Left -(mousedownspot.X-x);
 c.top :=c.top -(mousedownspot.y-y);
 end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
c:=tcontrol.Create(self);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
c.Free;
end;

end.