同名派生的应用

有时候，我们需要少量修改或增加已有控件的行为或属性，但又不想新写个控件注册到组件面板上或动态创建来用，可以通过同名控件派生来实现。 以下这个简单的例子，为 TPanel 增加了 OnPaint 事件： unit Unit1; interface uses   Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,   Dialogs, StdCtrls, ExtCtrls; type   // 以相同类名派生一个子类   TPanel = class(ExtCtrls.TPanel)   private     FOnPaint: TNotifyEvent;   protected     // 重载一个方法     procedure Paint; override;   public     // 新定义一个事件     property OnPaint: TNotifyEvent read FOnPaint write FOnPaint;   end;   TForm1 = class(TForm)     pnl1: TPanel;     procedure FormCreate(Sender: TObject);   private     { Private declarations }     procedure OnPnlPaint(Sender: TObject);   public     { Public declarations }   end; var   Form1: TForm1; implementation {$R *.dfm} { TPanel } procedure TPanel.Paint; begin   inherited;   if Assigned(FOnPaint) then     FOnPaint(Self); end; procedure TForm1.FormCreate(Sender: TObject); begin   // 新增加的事件只能在运行期动态关联   pnl1.OnPaint := OnPnlPaint; end; procedure TForm1.OnPnlPaint(Sender: TObject); begin   // 这一句是可以执行到的   pnl1.Canvas.TextOut(10, 10, 'Test'); end; end.

按上面的方法，也可以这样。 unit Unit1; interface uses   Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,   Dialogs, Buttons, StdCtrls; type   TSpeedButton = class(TButton)   public     constructor Create(Aowner: TComponent); override;   end;   TForm1 = class(TForm)     SpeedButton1: TSpeedButton;   private     { Private declarations }   public     { Public declarations }   end; var   Form1: TForm1; implementation {$R *.dfm} { TSpeedButton } constructor TSpeedButton.Create(Aowner: TComponent); begin   inherited Create(AOwner);   Caption := 'TSpeedButton to TButton'; end; end.