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.

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通过传统的继承法让 TBevel 相应双击事件:

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unit Unit1;interfaceusesWindows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,Dialogs, ExtCtrls;typeTForm1 = class(TForm)procedure FormCreate(Sender: TObject);end;varForm1: TForm1;implementation{$R *.dfm}typeTMyBevel = class(TBevel)protectedprocedure DblClick; override;end;procedure TMyBevel.DblClick;
begininherited;ShowMessage(ClassName);
end;//
procedure TForm1.FormCreate(Sender: TObject);
beginwith TMyBevel.Create(Self) dobeginLeft := 10;Top := 10;Parent := Self;end;
end;end.

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

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unit Unit1;interfaceusesWindows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,Dialogs, ExtCtrls;typeTForm1 = class(TForm)Bevel1: TBevel;procedure FormCreate(Sender: TObject);privateprocedure MyDbClick(Sender: TObject);publicend;varForm1: TForm1;implementation{$R *.dfm}procedure TForm1.FormCreate(Sender: TObject);
beginTForm(Bevel1).OnDblClick := MyDbClick;
end;procedure TForm1.MyDbClick(Sender: TObject);
beginShowMessage(TComponent(Sender).Name);
end;end.

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

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unit Unit1;interfaceusesWindows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,Dialogs, ExtCtrls;typeTForm1 = class(TForm)Bevel1: TBevel;procedure FormCreate(Sender: TObject);privateprotectedprocedure 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);publicend;varForm1: TForm1;implementation{$R *.dfm}vara,b: Integer;f: Boolean;procedure TForm1.FormCreate(Sender: TObject);
beginTForm(Bevel1).OnMouseDown := MyMouseDown;TForm(Bevel1).OnMouseMove := MyMouseMove;TForm(Bevel1).OnMouseUp := MyMouseUp;
end;procedure TForm1.MyMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
beginf := True;a := X;b := Y;
end;procedure TForm1.MyMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
beginif f then with TControl(Sender) dobeginLeft := Left + X - a;Top := Top + Y - b;end;
end;procedure TForm1.MyMouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
beginf := False;
end;end.

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