end;

end;

procedure TBag.Change;

begin

  if not Locked then

    if Assigned(FOnChange) then FOnChange(Self);

end;

procedure TBag.SetLocking(Updating: Boolean);

begin

  if Updating then { Bag has become unlocked }

    Change;

end;

Delphi实例：TString、TstringList

TStrings = class(TPersistent)

  private

FUpdateCount: Integer;

  Protected

procedure Exchange(Index1, Index2: Integer); virtual;

procedure SetUpdateState(Updating: Boolean); virtual;

public

  procedure BeginUpdate;

  procedure EndUpdate;

procedure Changed; virtual;

       procedure Changing; virtual;

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