详测 Generics Collections TQueue (3): OnNotify、Extract

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 MyQueueNotify(Sender: TObject; const Item: Integer;

      Action: TCollectionNotification);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



//uses Generics.Collections;



{准备给 TQueue.OnNotify 调用的事件过程}

procedure TForm1.MyQueueNotify(Sender: TObject; const Item: Integer;

  Action: TCollectionNotification);

begin

  case Action of

    cnAdded     : ShowMessageFmt('Add: %d', [Item]);

    cnRemoved   : ShowMessageFmt('Remove: %d', [Item]);

    cnExtracted : ShowMessageFmt('Extract: %d', [Item]);

  end;

end;



procedure TForm1.Button1Click(Sender: TObject);

var

  Queue: TQueue<Integer>;

begin

  Queue := TQueue<Integer>.Create();

  Queue.OnNotify := MyQueueNotify;



  Queue.Enqueue(11); {Add: 11}

  Queue.Enqueue(22); {Add: 22}

  Queue.Enqueue(33); {Add: 33}



  Queue.Dequeue;     {Remove: 11}



  // Extract 和 Dequeue 功能一致, 区别只是在驱动 OnNotify 事件时传递的参数有区别, 没多大意义

  Queue.Extract;     {Extract: 22}



  //Queue.OnNotify := nil;



  Queue.Free;        {Remove: 33}

end;



end.