五种情况下会刷新控件状态（刷新所有子FWinControls的显示）——从DFM读取数据时新增加子控件时重新创建当前控件的句柄时设置父控件时显示状态被改变时

Posted 2020-07-06 朝闻道

五种情况下会刷新控件状态（刷新控件状态才能刷新所有子FWinControls的显示）：

在TWinControls.PaintControls中，对所有FWinControls只是重绘了边框，而没有整个重绘这些FWinControl子控件。那么什么时候才整个重绘全部FWinControls呢？这时候，就不是一个单纯的WM_PAINT来解决控件重绘的问题了，而是这个TWinControl.UpdateShowing函数：

procedure TWinControl.UpdateShowing;
var
  ShowControl: Boolean;
  I: Integer;
begin
  ShowControl := (FVisible or (csDesigning in ComponentState) and
    not (csNoDesignVisible in ControlStyle)) and
    not (csReadingState in ControlState);
  if ShowControl then
  begin
    if FHandle = 0 then CreateHandle;
    if FWinControls <> nil then
      for I := 0 to FWinControls.Count - 1 do
        TWinControl(FWinControls[I]).UpdateShowing;
  end;
  if FHandle <> 0 then
    if FShowing <> ShowControl then
    begin
      FShowing := ShowControl;
      try
        Perform(CM_SHOWINGCHANGED, 0, 0);
      except
        FShowing := not ShowControl;
        raise;
      end;
    end;
end;

那么什么时候才会调用TWinControl.UpdateShowing;呢？回答是，就一种情况下：当控件状态改变的时候：

procedure TWinControl.UpdateControlState;
var
  Control: TWinControl;
begin
  Control := Self;
  while Control.Parent <> nil do
  begin
    Control := Control.Parent;
    if not Control.Showing then Exit;
  end;
  if (Control is TCustomForm) or (Control.FParentWindow <> 0) then UpdateShowing; // 必须有父窗口，才给显示。TCustomForm那已经是顶级窗口
end;

那么什么时候算控件状态改变？回答是，一共五种情况：从DFM读取数据时、新增加子控件时、重新创建当前控件的句柄时、设置父控件时、显示状态被改变时：

// 情况一：
procedure TWinControl.ReadState(Reader: TReader);
begin
  DisableAlign;
  try
    inherited ReadState(Reader);
  finally
    EnableAlign;
  end;
  FixupTabList;
  if FParent <> nil then Perform(CM_PARENTCTL3DCHANGED, 0, 0);
  UpdateControlState;
end;

// 情况二：
procedure TWinControl.InsertControl(AControl: TControl);
begin
  AControl.ValidateContainer(Self);
  Perform(CM_CONTROLLISTCHANGE, Integer(AControl), Integer(True));
  Insert(AControl);
  if not (csReading in AControl.ComponentState) then
  begin
    AControl.Perform(CM_PARENTCOLORCHANGED, 0, 0);
    AControl.Perform(CM_PARENTFONTCHANGED, 0, 0);
    AControl.Perform(CM_PARENTSHOWHINTCHANGED, 0, 0);
    AControl.Perform(CM_PARENTBIDIMODECHANGED, 0, 0);
    if AControl is TWinControl then
    begin
      AControl.Perform(CM_PARENTCTL3DCHANGED, 0, 0);
      UpdateControlState;
    end else
      if HandleAllocated then AControl.Invalidate;
    AlignControl(AControl);
  end;
  Perform(CM_CONTROLCHANGE, Integer(AControl), Integer(True));
end;

// 情况三：
procedure TWinControl.CMRecreateWnd(var Message: TMessage);
var
  WasFocused: Boolean;
begin
  WasFocused := Focused;
  DestroyHandle;
  UpdateControlState;
  if WasFocused and (FHandle <> 0) then Windows.SetFocus(FHandle);
end;

// 情况四：
procedure TWinControl.SetParentWindow(Value: HWnd); 
begin
  if (FParent = nil) and (FParentWindow <> Value) then
  begin
    if (FHandle <> 0) and (FParentWindow <> 0) and (Value <> 0) then
    begin
      FParentWindow := Value;
      Windows.SetParent(FHandle, Value);
      if (Win32MajorVersion >= 5) and (Win32Platform = VER_PLATFORM_WIN32_NT) then
        Perform(WM_CHANGEUISTATE, MakeWParam(UIS_INITIALIZE, UISF_HIDEACCEL or UISF_HIDEFOCUS), 0);
    end else
    begin
      DestroyHandle;
      FParentWindow := Value;
    end;
    UpdateControlState;
  end;
end;

// 情况五：
procedure TWinControl.CMVisibleChanged(var Message: TMessage);
begin
  if not FVisible and (Parent <> nil) then RemoveFocus(False);
  if not (csDesigning in ComponentState) or
    (csNoDesignVisible in ControlStyle) then UpdateControlState;
end;

但是还是有个问题，在TWinControl.UpdateShowing里执行了CM_SHOWINGCHANGED消息，也就是：

procedure TWinControl.CMShowingChanged(var Message: TMessage);
const
  ShowFlags: array[Boolean] of Word = (
    SWP_NOSIZE + SWP_NOMOVE + SWP_NOZORDER + SWP_NOACTIVATE + SWP_HIDEWINDOW,
    SWP_NOSIZE + SWP_NOMOVE + SWP_NOZORDER + SWP_NOACTIVATE + SWP_SHOWWINDOW);
begin
  SetWindowPos(FHandle, 0, 0, 0, 0, 0, ShowFlags[FShowing]);
end;

可是SetWindowPos会触发WM_PAINT消息吗？看MSDN没有这么说啊，那么显示所有WinControl子控件和调用它的WM_PAINT真正自绘，两者怎样才能联系起来呢？