Windows 消息【二】窗口函数

前一篇文章讲到非队列消息会直接把消息Dispatch到窗口函数上，窗口函数长什么样？

//就是一个大case分支
//要想拦截消息，override窗口函数是一个办法！
procedure TCustomForm.WndProc(var Message: TMessage);
var
  FocusHandle: HWND;
  SaveIndex: Integer;
  MenuItem: TMenuItem;
  Canvas: TCanvas;
  DC: HDC;
begin
  with Message do
    case Msg of
      WM_ACTIVATE, WM_SETFOCUS, WM_KILLFOCUS:
        begin
        end;
      CM_EXIT:
        if HostDockSite <> nil then DeActivate;
    end;
end;

假如我们要用这种方法拦截Edit的Copy,Cut消息怎么办？

难道我们还要继承CustomEdit,再override窗口函数，生成新的MyEdit?有人想，直接用一个函数先把CustomEdit的WndProc替换掉不就行了，使用完毕后，再还原！

//替换窗口函数
 TForm1 = class(TForm)
    edt1: TEdit;
    btn1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    FOldWndProc:  TWndMethod;

    { Private declarations }
  public
    { Public declarations }
      procedure  NewWndProc(var  Message:  TMessage);  

  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure  TForm1.NewWndProc(var  Message:  TMessage);
begin
    if  (Message.Msg  <>  WM_CUT)  and  (Message.Msg  <>  WM_COPY)  and
        (Message.Msg  <>  WM_PASTE)  then
        FOldWndProc(Message);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
   FOldWndProc  :=  edt1.WindowProc;
   edt1.WindowProc  :=  NewWndProc;

end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  edt1.WindowProc  :=  FOldWndProc;
end;
end.