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WindowsCE.[Essential Windows CE Application Programming].Jon Wiley & Son.zip

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<B>Essential Windows CE Application Programming</B>
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<I>(Publisher: John Wiley & Sons, Inc.)</I>
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Author(s): Robert Burdick
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ISBN: 0471327476
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Publication Date: 03/01/99
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<P><FONT SIZE="+1"><B>The WM_CREATE Message</B></FONT></P>
<P>The <I>CreateWindow</I> and <I>CreateWindowEx</I> functions both send a WM_CREATE message to the window procedure of the window being created. This message is sent after the window has been created but before it becomes visible. Furthermore, the WM_CREATE message is sent before the <I>CreateWindow</I> and <I>CreateWindowEx</I> functions return.</P>
<P>As Table 2.2 shows, the WM_CREATE message passes a pointer to a CREATESTRUCT structure containing information about the window being created. Here is the definition of the CREATESTRUCT structure:</P>
<!-- CODE //-->
<PRE>
  typedef struct tagCREATESTRUCT
  &#123;
    LPVOID lpCreateParams;
    HINSTANCE hInstance;
    HMENU hMenu;
    HWND hwndParent;
    int cy;
    int cx;
    int y;
    int x;
    LONG style;
    LPCTSTR lpszName;
    LPCTSTR lpszClass;
    DWORD dwExStyle;
  &#125; CREATESTRUCT, *LPCREATESTRUCT;
</PRE>
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<TABLE WIDTH="100%" BORDER RULES="ROWS">
<CAPTION ALIGN=LEFT><B>Table 2.2</B> The WM_CREATE Message Parameters
<TR>
<TH WIDTH="30%" ALIGN="LEFT">PARAMETER
<TH WIDTH="70%" ALIGN="LEFT">MEANING
<TR>
<TD>wParam
<TD>Not used
<TR>
<TD VALIGN="TOP">(LPCREATESTRUCT)lParam
<TD>Pointer to the CREATESTRUCT structure containing information about the window being created
</TABLE>
<P>The <I>lpCreateParams</I> member of CREATESTRUCT contains the <I>lpParam</I> passed to the <I>CreateWindow</I> or <I>CreateWindowEx</I> call that generated the WM_CREATE message. If you use the <I>lpParam</I> parameter of <I>CreateWindow</I> or <I>CreateWindowEx</I> to pass some application-specific value for use during window creation, your application extracts it from this member.</P>
<P><I>hInstance</I> identifies the module (application or dynamic link library) that owns the window that was just created.</P>
<P><I>hMenu</I> identifies the window menu. As we&#146;ll see later in Chapter 4, windows do not support menu bars under Windows CE. The <I>hMenu</I> member will therefore be NULL unless the window created is a child window. In that case this member will contain the child window identifier.</P>
<P><I>hwndParent</I> contains the HWND of the parent of the newly created window.</P>
<P><I>cx</I>, <I>cy</I>, <I>y</I>, and <I>x</I> are the width, height, y position, and x position of the window, respectively. For top-level windows such as overlapped or pop-up windows, these values are given in screen coordinates. For child windows, these coordinates are relative to the upper left corner of the window&#146;s parent.</P>
<P>The <I>style</I> and <I>dwExStyle</I> members are DWORD values containing the style and extended style bits defined for the newly created window. In other words, these members are exactly the same as the <I>dwStyle</I> and <I>dwExStyle</I> values passed to <I>CreateWindow</I> or <I>CreateWindowEx</I>.</P>

<TABLE BORDER="2" BORDERCOLOR="#0000" ALIGN="CENTER">
<TR><TD><FONT SIZE="+1"><B>Adding or Removing Styles after a Window Has Been Created</B></FONT>
<P>It is common to want to add or remove window styles or extended styles from windows after they have been created. You can do this using the <I>GetWindowLong</I> and <I>SetWindowLong</I> functions.</P>
<P>For example, let&#146;s say you want to disable scrolling in a window programmatically. An application would do this:</P>
<!-- CODE SNIP //-->
<PRE>
  //hwndNoScroll is the window of interest
  DWORD dwStyle;
  //Get the current set of window style bits
  dwStyle = GetWindowLong(hwndNoScroll, GWL_STYLE);
  //Disable WS_VSCROLL, WS_HSCROLL
  SetWindowLong(hwndNoScroll, GWL_STYLE,
      (dwStyle &#38; &#8764;(WS_VSCROLL | WS_HSCROLL)
</PRE>
<!-- END CODE SNIP //-->
</TABLE>

<P>Finally, <I>lpszName</I> and <I>lpszClass</I> contain the window caption and window class name, respectively, of the newly created window.</P>
<P>The value that an application returns in response to the WM_CREATE message controls the value returned by the <I>CreateWindow</I> and <I>CreateWindowEx</I> functions that triggered the WM_CREATE message. If an application returns 0 (zero) in response to this message, <I>CreateWindow</I> and <I>CreateWindowEx</I> continue with their normal execution. When the functions finish, they return the HWND of the window that was created.</P>
<P>On the other hand, if the application returns &#150;1 in response to WM_CREATE, the new window is destroyed and <I>CreateWindow</I> and <I>CreateWindowEx</I> return NULL.</P>
<P>Applications respond to the WM_CREATE message to implement custom window creation behavior or to take more control of the window creation process.</P>
<P>As a very contrived example, let&#146;s say that we are writing an application that includes a registered window class with a window procedure named <I>WideWndProc</I>. Our application wants to refuse to create any instance of this class that is not at least 300 pixels wide.</P>
<P>To implement this feature, the WM_CREATE message handler of <I>WideWndProc</I> would look like this:</P>
<!-- CODE //-->
<PRE>
  LRESULT CALLBACK WideWndProc(
    HWND hwnd,
    UINT message,
    WPARAM wParam,
    LPARAM lParam)
  &#123;
    switch(message)
    &#123;
     case WM_CREATE:
      LPCREATESTRUCT lpcs;
      lpcs = (LPCREATESTRUCT)lParam;
      if (lpcs-&gt;cx &lt; 300)
      &#123;
       return (-1);
      &#125;
      return (0);
     &#133;
  &#125;
</PRE>
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