Application.HookMainWindow完全替代了原来的窗口过程（但是好像也会继续传递）

unit HookMain;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls, ExtCtrls;

type
  THookForm = class(TForm)
    SendBtn: TButton;
    GroupBox1: TGroupBox;
    LogList: TListBox;
    DoLog: TCheckBox;
    ExitBtn: TButton;
    Button1: TButton;
    procedure SendBtnClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure ExitBtnClick(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    function AppWindowHook(var Message: TMessage): Boolean;
  end;

var
  HookForm: THookForm;

implementation

{$R *.DFM}

procedure THookForm.FormCreate(Sender: TObject);
begin
  Application.HookMainWindow(AppWindowHook);
end;

procedure THookForm.FormDestroy(Sender: TObject);
begin
  Application.UnhookMainWindow(AppWindowHook);
end;

function THookForm.AppWindowHook(var Message: TMessage): Boolean;
const
  LogStr = ‘Message ID: $%x, WParam: $%x, LParam: $%x‘;
begin
  Result := True;
  if DoLog.Checked then
    with Message do
      LogList.Items.Add(Format(LogStr, [Msg, WParam, LParam]));
end;

procedure THookForm.SendBtnClick(Sender: TObject);
begin
  SendMessage(Application.Handle, WM_NULL, 0, 0);
end;

procedure THookForm.ExitBtnClick(Sender: TObject);
begin
  Close;
end;

procedure THookForm.Button1Click(Sender: TObject);
begin
    ShowMessage(‘ddd‘);
end;

end.