Delphi中繼承方式使用控件

以前寫代碼, 總是把主單元弄得滿滿當當; 現在更喜歡把控件比較獨立的功能寫成一個單元, 改寫屬性、 重載方法...哪怕只有一點點和默認不同, 也喜歡獨立出來. 剛剛用到 TListBox, 需要能拖動元素、雙擊刪除.

unit ListBox2;
 
interfaceuses
  System.Classes, Vcl.Controls, Vcl.StdCtrls, System.Types;
 
type
  TListBox2 = class(TCustomListBox)
  protectedprocedure DragOver(Source: TObject; X: Integer; Y: Integer; State: TDragState; var 

Accept: Boolean); override;procedure DblClick; override;
  publicconstructor Create(AOwner: TComponent); override;procedure DragDrop(Source: TObject; X: 

Integer; Y: Integer); override;
  end;
 
implementation{ TListBox2 }constructor TListBox2.Create(AOwner: TComponent);
begin
  inherited;
  DragMode := dmAutomatic;
end;
 
procedure TListBox2.DblClick;
begin
  inherited;
  Items.Delete(ItemIndex);
end;
 
procedure TListBox2.DragDrop(Source: TObject; X, Y: Integer);
begin
  inherited;
  Items.Exchange(ItemIndex, ItemAtPos(Point(X,Y), True));
end;
 
procedure TListBox2.DragOver(Source: TObject; X, Y: Integer; State: TDragState; var Accept: 

Boolean);
begin
  inherited;
  Accept := True;
end;
 
end.

測試:

uses ListBox2;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
  with TListBox2.Create(Self) dobeginParent := Self;
    Align := alLeft;
    Items.CommaText := 'A,B,C,D,E,F,G';
  end;
end;