ITPub博客

首页 > 应用开发 > IT综合 > VCL中消息处理初探 (转)

VCL中消息处理初探 (转)

原创 IT综合 作者:worldblog 时间:2007-12-10 10:57:47 0 删除 编辑
VCL中消息处理初探 (转)[@more@]

Tobject是基类,所以我们先看一下TObject的DISPATCH方法。Dispatch根据传入的message来寻找相应的消息处理方法,如果找不到的话,就继续向上到父类的消息处理方法表中寻找响应的处理方法,一直到找到为止,如果找到顶还没有,则调用DefaultHandle来处理该消息。message可以是任何的类型,Dispatch假设message的头两位是消息的ID,它就是根据ID来寻找消息处理方法的。虽然任何类型的message都可以被接受,但是TObject的子类还是希望传入的message参数是TMessage的记录类型或其他证明的记录类型。
以下声明和注释摘自与system.pas:
{ TObject.Dispatch accepts any data type as its Message parameter.  The
  first 2 bytes of the data are taken as the message id to search for
  in the object's message methods.  TDispatchMessage is an example of
  such a structure with a word field for the message id.
}
  TDispatchMessage = record
  MsgID: Word;
  end;
类的继承关系如下:
TObject->TPersistent->TComponent->TControl
TControl是所以可视化组件的父类,TControl提供了一个新的方法,WndProc:
procedure TControl.WndProc(var Message: TMessage);
var
  Form: TCustomForm;
  KeyState: TKeyboardState; 
  WheelMsg: TCMMouseWheel;
begin
  //如果处在设计期
  if (csDesigning in ComponentState) then
  begin
  FoRM := GetParentForm(Self);//得到拥有该组件的窗体
  if (Form <> nil) and (Form.Designer <> nil) and
  Form.Designer.IsDesignMsg(Self, Message) then Exit //消息由窗体来处理
  end;

  //窗体可以为其拥有的组件来处理键盘消息。
  if (Message.Msg >= WM_KEYFIRST) and (Message.Msg <= WM_KEYLAST) then
  begin
  Form := GetParentForm(Self);
  if (Form <> nil) and Form.WantChildKey(Self, Message) then Exit;
  end

  //关于鼠标的消息
  else if (Message.Msg >= WM_MOUSEFIRST) and (Message.Msg <= WM_MOUSELAST) then
  begin
  //如果组件不可以接受和处理双击消息,就将双击消息映射为单击消息。
  if not (csDoubleClicks in ControlStyle) then
  case Message.Msg of
  WM_LBUTTONdbLCLK, WM_RBUTTONDBLCLK, WM_MBUTTONDBLCLK:
  Dec(Message.Msg, WM_LBUTTONDBLCLK - WM_LBUTTONDOWN);
  end;
 
  case Message.Msg of
  WM_MOUSEMOVE: Application.HintMouseMessage(Self, Message);//如果是鼠标移动的消息,则出现hint窗口
  WM_LBUTTONDOWN, WM_LBUTTONDBLCLK://如果是左键被按下,或者双击,如果是自动拖动模式,则开始拖动,并将左键按下的状态加入组件的状态。
  begin
  if FDragMode = dmAutomatic then
  begin
  BeginAutoDrag;
  Exit;
  end;
  Include(FControlState, csLButtonDown);
  end;
  WM_LBUTTONUP:
  Exclude(FControlState, csLButtonDown); //如果是左键放开,则将左键按下的状态剔除。
  else
  with Mouse do
  if WheelPresent and (RegWheelMessage <> 0) and  //如果鼠标有滚轮,并且滚轮滑动时发出了消息
  (Message.Msg = RegWheelMessage) then
  begin
  GetKeyboardState(KeyState);  //将256虚拟键的状态拷贝到缓存中去
  with WheelMsg do //填充记录
  begin
  Msg := Message.Msg;
  ShiftState := KeyboardStateToShiftState(KeyState);
  WheelDelta := Message.WParam;
  Pos := TSmallPoint(Message.LParam);
  end;
  MouseWheelHandler(TMessage(WheelMsg)); //派发鼠标滚轮的消息
  Exit;
  end;
  end;
  end
  else if Message.Msg = CM_VISIBLECHANGED then
  with Message do
  SendDockNotification(Msg, WParam, LParam);  //处理自定义消息
  Dispatch(Message); //派发未处理的消息
end;
但是只有TWinControl可以获得焦点:
procedure TWinControl.WndProc(var Message: TMessage);
var
  Form: TCustomForm;
begin
  case Message.Msg of
  WM_SETFOCUS:  //设置控件的焦点
  begin
  Form := GetParentForm(Self);
  if (Form <> nil) and not Form.SetFocusedControl(Self) then Exit;
  end;
  WM_KILLFOCUS:
  if csfocusing in ControlState then Exit;
  //当鼠标有活动的时候发出该消息,如果鼠标没有被捕捉到,则消息发往鼠标下面的那个窗口,否则消息将发往捕捉到鼠标的那个窗口。
  WM_NCHITTEST:
  begin
  inherited WndProc(Message); //调用父类的处理方法
  //如果窗体被挡住并且在指定的点没有控件,则返回结果为在client区。
  if (Message.Result = HTTRANSPARENT) and (ControlAtPos(ScreenToClient(
  SmallPointToPoint(TWMNCHitTest(Message).Pos)), False) <> nil) then
  Message.Result := HTCLIENT;
  Exit;
  end;
  WM_MOUSEFIRST..WM_MOUSELAST:
  if ISCOntrolMouseMsg(TWMMouse(Message)) then  //鼠标消息是否直接发往组件的窗体子组件
  begin
  { Check HandleAllocated because IsControlMouseMsg might have freed the
  window if user code executed something like Parent := nil. }
  if (Message.Result = 0) and HandleAllocated then
  DefWindowProc(Handle, Message.Msg, Message.wParam, Message.lParam);//调用默认的的消息处理方法对该消息进行默认处理。
  Exit;
  end;
  WM_KEYFIRST..WM_KEYLAST:
  if Dragging then Exit;
  WM_CANCELMODE:
  if (GetCapture = Handle) and (CaptureControl <> nil) and
  (CaptureControl.Parent = Self) then
  CaptureControl.Perform(WM_CANCELMODE, 0, 0);
  end;
  inherited WndProc(Message);
end;

TApplication在程序中发挥着重要的作用:
Application.Run;

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;

  //一个消息循环直到TeRminated为True时才退出。
  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;
  if PeekMessage(Msg, 0, 0, 0, PM_REMOVE) then  //从现成的消息循环中取出消息并放入指定的消息结构中。
  begin
  Result := True;
  if Msg.Message <> WM_QUIT then  //如果不是退出消息则进行相应的处理
  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
  TranslateMessage(Msg);
  DispatchMessage(Msg);
  end;
  end
  else
  FTerminate := True;
  end;
end;


来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/10752043/viewspace-990901/,如需转载,请注明出处,否则将追究法律责任。

请登录后发表评论 登录
全部评论
  • 博文量
    6241
  • 访问量
    2410344