Why can't I custom a CButton's,CEdit shape by extended it?

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MFC

Dear All,
I have read the article here, and try to custom some Windows Controls by extending it to a new one.

First, I extended a CSliderCtrl class to a new RoundedRectangle one.
And it works!
But when I transplant the method and code to custom a RoundedRectangle CEdit or CButton.
It failed.
Why does it happend?
Below are my code.

I only override the
1. PreCreateWindow
2. PreSubClassWindow
3. OnPaint

below code is for changing the shape of it.

CRect rect;
GetClientRect(&rect);int w = rect.Width();//the rect width
int h = rect.Height();//the rect height
int uper_left_x=rect.TopLeft().x;
int uper_left_y=rect.TopLeft().y;
int lower_right_x=rect.BottomRight().x;
int lower_right_y=rect.BottomRight().y;
int elipse_width=lower_right_y-uper_left_y;//the obtuse angle size
int elipse_height=elipse_width;//the obuse angle sizeCRgn rgn1;
SetWindowRgn(NULL, FALSE);

	//modify this to larger
bool b=rgn1.CreateRoundRectRgn(uper_left_x,uper_left_y,lower_right_x,lower_right_y,elipse_width,elipse_height);
SetWindowRgn(rgn1, TRUE);

Thease code works fine with extended CSliderCtrl, but fail on extended CButton and CEdit,which can't change shape like the exteded CSliderCtrl.

Could someone help me to slove this?^^

Thanks in advance.