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 = then CreateHandle;
if FWinControls <> nil then
for I := to FWinControls.Count - do
TWinControl(FWinControls[I]).UpdateShowing;
end;
if FHandle <> then
if FShowing <> ShowControl then
begin
FShowing := ShowControl;
try
Perform(CM_SHOWINGCHANGED, , );
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*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, , );
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, , );
AControl.Perform(CM_PARENTFONTCHANGED, , );
AControl.Perform(CM_PARENTSHOWHINTCHANGED, , );
AControl.Perform(CM_PARENTBIDIMODECHANGED, , );
if AControl is TWinControl then
begin
AControl.Perform(CM_PARENTCTL3DCHANGED, , );
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 <> ) then Windows.SetFocus(FHandle);
end; // 情况四：
procedure TWinControl.SetParentWindow(Value: HWnd);
begin
if (FParent = nil) and (FParentWindow <> Value) then
begin
if (FHandle <> ) and (FParentWindow <> ) and (Value <> ) then
begin
FParentWindow := Value;
Windows.SetParent(FHandle, Value);
if (Win32MajorVersion >= ) and (Win32Platform = VER_PLATFORM_WIN32_NT) then
Perform(WM_CHANGEUISTATE, MakeWParam(UIS_INITIALIZE, UISF_HIDEACCEL or UISF_HIDEFOCUS), );
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, , , , , , 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？