详测 Generics Collections TList (10): OnNotify 事件

最新推荐文章于 2021-08-13 10:10:34 发布

转载最新推荐文章于 2021-08-13 10:10:34 发布 · 111 阅读

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本文介绍使用Delphi实现TList<string>的基本操作及其通知事件的应用，包括添加、删除和提取元素等，并展示了如何通过OnNotify事件来监控列表的变化。

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, Generics.Collections;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    procedure MyListNotify(Sender: TObject; const Item: string;
      Action: TCollectionNotification);
  end;
 
var
  Form1: TForm1;

implementation

{$R *.dfm}

{准备给 List.OnNotify 调用的事件过程}
procedure TForm1.MyListNotify(Sender: TObject; const Item: string; 
  Action: TCollectionNotification);
begin
  case Action of
    cnAdded     : ShowMessageFmt('Add: %s', [Item]);
    cnRemoved   : ShowMessageFmt('Remove: %s', [Item]);
    cnExtracted : ShowMessageFmt('Extract: %s', [Item]);
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  List: TList<string>;
begin
  List := TList<string>.Create();
  List.OnNotify := MyListNotify; {关联事件过程}

  List.AddRange(['A', 'B', 'C']); {Add: A | Add: B | Add: C }

  List.Delete(0);    {Remove: A}
  List.Remove('B');  {Remove: B}
  List.Extract('C'); {Extract: C}

  List.OnNotify := nil;    
  List.Free;
end;

end.