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.