program WindowDemo;
uses Windows, Messages;
// 窗口函数，窗口接到消息时被Windows所调用
function WindowProc(hwnd : HWND; uMsg : Cardinal; wParam : WPARAM;
lParam : LPARAM) : LResult; stdcall;
begin
Result := 0;
case uMsg of
// 关闭窗口消息，当用户关闭窗口后，通知主消息循环结束程序
WM_CLOSE : PostMessage(hwnd, WM_QUIT, 0, 0);
// 鼠标左键按下消息
WM_LBUTTONDOWN : MessageBox(hwnd, 'Hello!', '和您打个招呼',
MB_ICONINFORMATION);
else
// 其他消息做默认处理
Result := DefWindowProc(hWnd, uMsg, wParam, lParam);
end;
end;
var
wndcls : WNDCLASS; // 窗口类的记录（结构）类型
hWnd : THandle;
Msg : tagMSG; // 消息类型
begin
wndcls.style := CS_DBLCLKS; // 允许窗口接受鼠标双击
wndcls.lpfnWndProc := @WindowProc; // 为窗口类指定窗口函数
wndcls.cbClsExtra := 0;
wndcls.cbWndExtra := 0;
wndcls.hInstance := hInstance;
wndcls.hIcon := 0;
wndcls.hCursor := LoadCursor(hInstance, 'IDC_ARROW');
wndcls.hbrBackground := COLOR_WINDOWFRAME;
wndcls.lpszMenuName := nil;
wndcls.lpszClassName := 'WindowClassDemo'; // 窗口类名称
// 注册窗口类
if RegisterClass(wndcls) = 0 then
Exit;
// 创建窗口
hWnd := CreateWindow(
'WindowClassDemo', // 窗口类名称
'WindowDemo', // 窗口名称
WS_BORDER or WS_CAPTION or WS_SYSMENU, // 窗口类型
Integer(CW_USEDEFAULT),
Integer(CW_USEDEFAULT),
Integer(CW_USEDEFAULT),
Integer(CW_USEDEFAULT),
0,
0,
hInstance,
nil
);
if hWnd = 0 then
Exit;
// 显示窗口
ShowWindow(hWnd, SW_SHOWNORMAL);
UpdateWindow(hWnd);
// 创建主消息循环，处理消息队列中的消息并分发
// 直至收到WM_QUIT消息，退出主消息循环，并结束程序
// WM_QUIT消息由PostMessage()函数发送
while GetMessage(Msg, hWnd, 0, 0) do
begin
TranslateMessage(Msg);
DispatchMessage(Msg);
end;
end.

constructor TApplication.Create(AOwner: TComponent)
var
  
  if not IsLibrary then CreateHandle;
  
end;

procedure TApplication.CreateHandle;
var
  TempClass: TWndClass;
  SysMenu: HMenu;
begin
  if not FHandleCreated and not IsConsole then
  begin
    FObjectInstance := Classes.MakeObjectInstance(WndProc);
    // 如果窗口类不存在，则注册窗口类
    if not GetClassInfo(HInstance, WindowClass.lpszClassName, TempClass) then
    begin
      WindowClass.hInstance := HInstance;
      if Windows.RegisterClass(WindowClass) = 0 then
        raise EOutOfResources.Create(SWindowClass);
    end;
   // 创建窗口，长度和宽度都是0，位置在屏幕中央，返回的句柄FHandle
   // 也就是Tapplication.Handle的值
    FHandle := CreateWindow(WindowClass.lpszClassName, PChar(FTitle),
      WS_POPUP or WS_CAPTION or WS_CLIPSIBLINGS or WS_SYSMENU
      or WS_MINIMIZEBOX,
      GetSystemMetrics(SM_CXSCREEN) div 2,
      GetSystemMetrics(SM_CYSCREEN) div 2,
      0, 0, 0, 0, HInstance, nil);
    FTitle := '';
    FHandleCreated := True;
   // 调用SetWindowLong设置窗口的窗口函数（WndProc）
    SetWindowLong(FHandle, GWL_WNDPROC, Longint(FObjectInstance));
    if NewStyleControls then
    begin
      SendMessage(FHandle, WM_SETICON, 1, GetIconHandle);
      SetClassLong(FHandle, GCL_HICON, GetIconHandle);
    end;
    SysMenu := GetSystemMenu(FHandle, False);
    DeleteMenu(SysMenu, SC_MAXIMIZE, MF_BYCOMMAND);
    DeleteMenu(SysMenu, SC_SIZE, MF_BYCOMMAND);
    if NewStyleControls then DeleteMenu(SysMenu, SC_MOVE, MF_BYCOMMAND);
  end;
end;

procedure TApplication.CreateForm(InstanceClass: TComponentClass; var Reference);
var
  Instance: TComponent;
begin
  Instance := TComponent(InstanceClass.NewInstance);
  TComponent(Reference) := Instance;
  try
    Instance.Create(Self);
  except
    TComponent(Reference) := nil;
    raise;
  end;
   // 第一个创建的窗体实例就是MainForm
  if (FMainForm = nil) and (Instance is TForm) then
  begin
    TForm(Instance).HandleNeeded;
    FMainForm := TForm(Instance);
  end;
end;

procedure TApplication.Run;
begin
  FRunning := True;
  try
    AddExitProc(DoneApplication);
    if FMainForm <> nil then
    begin
      case CmdShow of
        SW_SHOWMINNOACTIVE: FMainForm.FWindowState := wsMinimized;
        SW_SHOWMAXIMIZED: MainForm.WindowState := wsMaximized;
      end;
      if FShowMainForm then
        if FMainForm.FWindowState = wsMinimized then
          Minimize else
          FMainForm.Visible := True;
      repeat
        try
          HandleMessage;
        except
          HandleException(Self);
        end;
      until Terminated;
    end;
  finally
    FRunning := False;
  end;
end;

procedure TApplication.HandleMessage;
var
  Msg: TMsg;
begin
  if not ProcessMessage(Msg) then Idle(Msg);
end;

function TApplication.ProcessMessage(var Msg: TMsg): Boolean;
var
  Handled: Boolean;
begin
  Result := False;
  // 取消息
  if PeekMessage(Msg, 0, 0, 0, PM_REMOVE) then
  begin
    Result := True;
    if Msg.Message <> WM_QUIT then
    begin
      Handled := False;
      if Assigned(FOnMessage) then FOnMessage(Msg, Handled);
      if not IsHintMsg(Msg) and not Handled and not IsMDIMsg(Msg) and
        not IsKeyMsg(Msg) and not IsDlgMsg(Msg) then
      begin
        // 熟悉的分发消息过程
        TranslateMessage(Msg);
        DispatchMessage(Msg);
      end;
    end
    else
      // 如果取到的消息为WM_QUIT，则将Fterminate设为真
       // 以通知主消息循环退出
       // 这和WindowDemo程序中判断GetMessage()函数返回值是否为0等效
       // 因为GetMessage()函数取出的消息如果是WM_QUIT，它的返回值为0
      FTerminate := True;
  end;
end;

procedure TApplication.WndProc(var Message: TMessage);
type // 函数内嵌定义的类型，只限函数内部使用
  TInitTestLibrary = function(Size: DWord; PAutoClassInfo: Pointer): Boolean; stdcall;

var
  I: Integer;
  SaveFocus, TopWindow: HWnd;
  InitTestLibrary: TInitTestLibrary;
  // 内嵌函数，默认的消息处理
   // 调用Windows的API函数DefWindowProc
  procedure Default;
  begin
    with Message do
      Result := DefWindowProc(FHandle, Msg, WParam, LParam);
  end;

  procedure DrawAppIcon;
  var
    DC: HDC;
    PS: TPaintStruct;
  begin
    with Message do
    begin
      DC := BeginPaint(FHandle, PS);
      DrawIcon(DC, 0, 0, GetIconHandle);
      EndPaint(FHandle, PS);
    end;
  end;

begin
  try
    Message.Result := 0;
    for I := 0 to FWindowHooks.Count - 1 do
      if TWindowHook(FWindowHooks[I]^)(Message) then Exit;
    CheckIniChange(Message);
    with Message do
      // 开始庞大的case分支，对不同的消息做出不同的处理
      case Msg of
        WM_SYSCOMMAND:
          case WParam and $FFF0 of
            SC_MINIMIZE: Minimize;
            SC_RESTORE: Restore;
          else
            Default;
          end;
        WM_CLOSE:
          if MainForm <> nil then MainForm.Close;
        WM_PAINT:
          if IsIconic(FHandle) then DrawAppIcon else Default;
        WM_ERASEBKGND:
          begin
            Message.Msg := WM_ICONERASEBKGND;
            Default;
          end;
        WM_QUERYDRAGICON:
          Result := GetIconHandle;
        WM_SETFOCUS:
          begin
            PostMessage(FHandle, CM_ENTER, 0, 0);
            Default;
          end;
        WM_ACTIVATEAPP:
          begin
            Default;
            FActive := TWMActivateApp(Message).Active;
            if TWMActivateApp(Message).Active then
            begin
              RestoreTopMosts;
              PostMessage(FHandle, CM_ACTIVATE, 0, 0)
            end
            else
            begin
              NormalizeTopMosts;
              PostMessage(FHandle, CM_DEACTIVATE, 0, 0);
            end;
          end;
        WM_ENABLE:
          if TWMEnable(Message).Enabled then
          begin
            RestoreTopMosts;
            if FWindowList <> nil then
            begin
              EnableTaskWindows(FWindowList);
              FWindowList := nil;
            end;
            Default;
          end else
          begin
            Default;
            if FWindowList = nil then
              FWindowList := DisableTaskWindows(Handle);
            NormalizeAllTopMosts;
          end;
        WM_CTLCOLORMSGBOX..WM_CTLCOLORSTATIC:
          Result := SendMessage(LParam, CN_BASE + Msg, WParam, LParam);
        WM_ENDSESSION: if TWMEndSession(Message).EndSession then FTerminate := True;
        WM_COPYDATA:
          if (PCopyDataStruct(Message.lParam)^.dwData = DWORD($DE534454)) and
            (FAllowTesting) then
            if FTestLib = 0 then
            begin
              FTestLib := SafeLoadLibrary('vcltest3.dll');
              if FTestLib <> 0 then
              begin
                Result := 0;
                @InitTestLibrary := GetProcAddress(FTestLib, 'RegisterAutomation');
                if @InitTestLibrary <> nil then
                  InitTestLibrary(PCopyDataStruct(Message.lParam)^.cbData,
                    PCopyDataStruct(Message.lParam)^.lpData);
              end
              else
              begin
                Result := GetLastError;
                FTestLib := 0;
              end;
            end
            else
              Result := 0;
        CM_ACTIONEXECUTE, CM_ACTIONUPDATE:
          Message.Result := Ord(DispatchAction(Message.Msg, TBasicAction(Message.LParam)));
        CM_APPKEYDOWN:
          if IsShortCut(TWMKey(Message)) then Result := 1;
        CM_APPSYSCOMMAND:
          if MainForm <> nil then
            with MainForm do
              if (Handle <> 0) and IsWindowEnabled(Handle) and
                IsWindowVisible(Handle) then
              begin
                FocusMessages := False;
                SaveFocus := GetFocus;
                Windows.SetFocus(Handle);
                Perform(WM_SYSCOMMAND, WParam, LParam);
                Windows.SetFocus(SaveFocus);
                FocusMessages := True;
                Result := 1;
              end;
        CM_ACTIVATE:
          if Assigned(FOnActivate) then FOnActivate(Self);
        CM_DEACTIVATE:
          if Assigned(FOnDeactivate) then FOnDeactivate(Self);
        CM_ENTER:
          if not IsIconic(FHandle) and (GetFocus = FHandle) then
          begin
            TopWindow := FindTopMostWindow(0);
            if TopWindow <> 0 then Windows.SetFocus(TopWindow);
          end;
        WM_HELP,   // MessageBox( MB_HELP)
        CM_INVOKEHELP: InvokeHelp(WParam, LParam);
        CM_WINDOWHOOK:
          if wParam = 0 then
            HookMainWindow(TWindowHook(Pointer(LParam)^)) else
            UnhookMainWindow(TWindowHook(Pointer(LParam)^));
        CM_DIALOGHANDLE:
          if wParam = 1 then
            Result := FDialogHandle
          else
            FDialogHandle := lParam;
        WM_SETTINGCHANGE:
          begin
            Mouse.SettingChanged(wParam);
            SettingChange(TWMSettingChange(Message));
            Default;
          end;
        WM_FONTCHANGE:
          begin
            Screen.ResetFonts;
            Default;
          end;
        WM_NULL:
          CheckSynchronize;  
      else
        Default;
      end;
  except
    HandleException(Self);
  end;
end;