<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;
xor eax,eax</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;
ret</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>WndProc
endp</font></font></font></b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1></font></font></font>
<p><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>EditWndProc
PROC hEdit:DWORD,uMsg:DWORD,wParam:DWORD,lParam:DWORD</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;
.if uMsg==WM_CHAR</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
mov eax,wParam</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.if (al>="0" &amp;&amp; al&lt;="9") || (al>="A" &amp;&amp; al&lt;="F")
|| (al>="a" &amp;&amp; al&lt;="f") || al==VK_BACK</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.if al>="a" &amp;&amp; al&lt;="f"</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
sub al,20h</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.endif</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
invoke CallWindowProc,OldWndProc,hEdit,uMsg,eax,lParam</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
ret</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.endif</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;
.elseif uMsg==WM_KEYDOWN</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
mov eax,wParam</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.if al==VK_RETURN</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
invoke MessageBox,hEdit,addr Message,addr AppName,MB_OK+MB_ICONINFORMATION</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
invoke SetFocus,hEdit</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.else</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
invoke CallWindowProc,OldWndProc,hEdit,uMsg,wParam,lParam</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
ret</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.endif</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;
.else</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
invoke CallWindowProc,OldWndProc,hEdit,uMsg,wParam,lParam</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
ret</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;
.endif</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;
xor eax,eax</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;
ret</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>EditWndProc
endp</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>end
start</font></font></font></b>
<h3>
<font face="Arial,Helvetica"><font color="#00CC00"><font size=+0>Analysis:</font></font></font></h3>

<ul><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
invoke SetWindowLong,hwndEdit,GWL_WNDPROC,addr EditWndProc</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
mov OldWndProc,eax</font></font></font></b></ul>
<font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>After
the edit control is created, we subclass it by calling SetWindowLong, replacing
the address of the original window procedure with our own window procedure.
Note that we store the address of the original window procedure for use
with CallWindowProc. Note the EditWndProc is an ordinary window procedure.</font></font></font>
<ul><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;
.if uMsg==WM_CHAR</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
mov eax,wParam</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.if (al>="0" &amp;&amp; al&lt;="9") || (al>="A" &amp;&amp; al&lt;="F")
|| (al>="a" &amp;&amp; al&lt;="f") || al==VK_BACK</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.if al>="a" &amp;&amp; al&lt;="f"</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
sub al,20h</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.endif</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
invoke CallWindowProc,OldWndProc,hEdit,uMsg,eax,lParam</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
ret</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.endif</font></font></font></b></ul>
<font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>Within
EditWndProc, we filter WM_CHAR messages. If the character is between 0-9
or a-f, we accept it by passing along the message to the original window
procedure. If it is a lower case character, we convert it to upper case
by adding it with 20h. Note that, if the character is not the one we expect,
we discard it. We don't pass it to the original window proc. So when the
user types something other than 0-9 or a-f, the character just doesn't
appear in the edit control.</font></font></font>
<ul><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;
.elseif uMsg==WM_KEYDOWN</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
mov eax,wParam</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.if al==VK_RETURN</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
invoke MessageBox,hEdit,addr Message,addr AppName,MB_OK+MB_ICONINFORMATION</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
invoke SetFocus,hEdit</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.else</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
invoke CallWindowProc,OldWndProc,hEdit,uMsg,wParam,lParam</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
ret</font></font></font></b>
<br><b><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.end</font></font></font></b></ul>
<font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>I want
to demonstrate the power of subclassing further by trapping Enter key.
EditWndProc checks WM_KEYDOWN message if it's VK_RETURN (the Enter key).
If it is, it displays a message box saying "You pressed the Enter key in
the text box!". If it's not an Enter key, it passes the message to the
original window procedure.</font></font></font>
<br><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>You
can use window subclassing to take control over other windows. It's one
of the powerful techniques you should have in your arsenal.</font></font></font>
<br>
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