学习 Message(5): 关于 TApplicationEvents.OnMessage 的第二个参数

TApplicationEvents.OnMessage 的第二个参数 Handled 如果是 True, 表示消息已经处理过了, 到此为止.

---

unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, AppEvnts, StdCtrls;



type

  TForm1 = class(TForm)

    Memo1: TMemo;

    ApplicationEvents1: TApplicationEvents;

    procedure ApplicationEvents1Message(var Msg: tagMSG; var Handled: Boolean);

    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;

      Shift: TShiftState; X, Y: Integer);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



procedure TForm1.ApplicationEvents1Message(var Msg: tagMSG;

  var Handled: Boolean);

begin

  if Msg.message = WM_LBUTTONDOWN then

  begin

    Memo1.Lines.Add('OnMessage');

    Handled := False; {Handled 默认是 False, 这句可以省略}

//    Handled := True;  {如果这样, 下面 OnMouseDown 事件将不会得到执行}

  end;

end;



procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;

  Shift: TShiftState; X, Y: Integer);

begin

  Memo1.Lines.Add('OnMouseDown');

end;



end.


 
   

我们可以利用这个特性来屏蔽一些消息, 譬如给 TWebBrowser 屏蔽右键菜单:

---

unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, OleCtrls, SHDocVw, AppEvnts;



type

  TForm1 = class(TForm)

    WebBrowser1: TWebBrowser;

    ApplicationEvents1: TApplicationEvents;

    procedure FormCreate(Sender: TObject);

    procedure ApplicationEvents1Message(var Msg: tagMSG; var Handled: Boolean);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



procedure TForm1.ApplicationEvents1Message(var Msg: tagMSG;

  var Handled: Boolean);

begin

  if IsChild(WebBrowser1.Handle, Msg.hwnd) and (Msg.message = WM_RBUTTONDOWN) then

  begin

    Handled := True;

  end;

end;



procedure TForm1.FormCreate(Sender: TObject);

begin

  WindowState := wsMaximized;

  WebBrowser1.Align := alTop;

  WebBrowser1.Navigate('http://www.cnblogs.com/del/');

end;



end.