唤醒控件曾经拥有的能力（重新继承是可以使用的.）

控件的祖先 TControl 有很多功能, 但它的有些子孙确丧失了很多(为了专用).

譬如 TBevel 就没有把一些常规的事件继承下来, 那些没有被继承的功能一般都隐藏在 protected 区, 如果重新继承是可以使用的.

这里尝试了另外一种方法: 自己没有继承时, 问一问有继承的兄弟、叔伯获取其它亲戚; 当然应先确保自己的祖先有该功能且没被覆盖过.

通过传统的继承法让 TBevel 相应双击事件:

unit Unit1;

interface

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

type
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

type
TMyBevel = class(TBevel)
protected
procedure DblClick; override;
end;

procedure TMyBevel.DblClick;
begin
inherited;
ShowMessage(ClassName);
end;

//
procedure TForm1.FormCreate(Sender: TObject);
begin
with TMyBevel.Create(Self) do
begin
Left := 10;
Top := 10;
Parent := Self;
end;
end;

end.

先在窗体上添加一个 TBevel, 它没有双击事件, 问一问 TForm 吧:

unit Unit1;

interface

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

type
TForm1 = class(TForm)
Bevel1: TBevel;
procedure FormCreate(Sender: TObject);
private
procedure MyDbClick(Sender: TObject);
public
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
TForm(Bevel1).OnDblClick := MyDbClick;
end;

procedure TForm1.MyDbClick(Sender: TObject);
begin
ShowMessage(TComponent(Sender).Name);
end;

end.

TBevel 通过 TForm 唤醒了对 OnMouseDown、OnMouseMove、OnMouseUp 的记忆, 从而实现被拖动的动能:

unit Unit1;

interface

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

type
TForm1 = class(TForm)
Bevel1: TBevel;
procedure FormCreate(Sender: TObject);
private
protected
procedure MyMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X: Integer; Y: Integer);
procedure MyMouseMove(Sender: TObject; Shift: TShiftState; X: Integer; Y: Integer);
procedure MyMouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X: Integer; Y: Integer);
public
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

var
a,b: Integer;
f: Boolean;

procedure TForm1.FormCreate(Sender: TObject);
begin
TForm(Bevel1).OnMouseDown := MyMouseDown;
TForm(Bevel1).OnMouseMove := MyMouseMove;
TForm(Bevel1).OnMouseUp := MyMouseUp;
end;

procedure TForm1.MyMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
f := True;
a := X;
b := Y;
end;

procedure TForm1.MyMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
begin
if f then with TControl(Sender) do
begin
Left := Left + X - a;
Top := Top + Y - b;
end;
end;

procedure TForm1.MyMouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
f := False;
end;

end.

http://www.cnblogs.com/del/archive/2011/05/12/2044112.html