atl under the hood - part 5.mht

大家知道wtl是window UI库

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      <DIV id=3Dcontentdiv><!-- Article Starts -->
      <UL class=3Ddownload>
        <LI><A=20
        =
href=3D"http://www.codeproject.com/atl/atl_underthehood_5/ATL_Under_The_H=
ood_Part_5_Src.zip">Download=20
        source code - 3.8 Kb</A> </LI></UL><!-- Add the rest of your =
HTML here -->
      <H2>Introduction</H2>
      <P>Lots of people thing that ATL is made only for making COM =
components.=20
      But in fact you can create full flash windows based application =
using ATL=20
      by using the Windowing classes of ATL. Although you can convert =
your MFC=20
      based project to ATL but there is very little support for UI =
component in=20
      ATL, so you have to write lots of code yourself. For instance =
there is no=20
      Document/View in ATL and if you want to make it then you have to =
implement=20
      it yourself. In this part we are going to explore the windowing =
classes.=20
      We also try to explore the techniques which ATL uses to do this. =
WTL=20
      (Window Template Library), was untill now unsupported by Microsoft =
and is=20
      in fact one step forward towards making graphical application. WTL =
is=20
      based on ATL Windowing classes. </P>Before starting the discussion =
of any=20
      ATL based program let's start our discussion with the classic =
Hello world=20
      program. This program is completely written in SDK and almost all =
of us=20
      are already familiar with it.=20
      <P><B>Program 66</B> </P><PRE><SPAN =
class=3Dcpp-preprocessor>#include &lt;windows.h&gt;</SPAN>

LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM =
lParam);

<SPAN class=3Dcpp-keyword>int</SPAN> WINAPI WinMain(HINSTANCE hInstance, =
HINSTANCE hPrevInstance,=20
                   LPSTR lpCmdLine,  <SPAN =
class=3Dcpp-keyword>int</SPAN> nCmdShow)
{
    <SPAN class=3Dcpp-keyword>char</SPAN> szAppName[] =3D <SPAN =
class=3Dcpp-string>"Hello world"</SPAN>;
    HWND hWnd;
    MSG msg;
    WNDCLASS wnd;
   =20
    wnd.cbClsExtra    =3D NULL;
    wnd.cbWndExtra    =3D NULL;
    wnd.hbrBackground    =3D (HBRUSH)GetStockObject(WHITE_BRUSH);
    wnd.hCursor    =3D LoadCursor(NULL, IDC_ARROW);
    wnd.hIcon        =3D LoadIcon(NULL, IDI_APPLICATION);
    wnd.hInstance    =3D hInstance;
    wnd.lpfnWndProc    =3D WndProc;
    wnd.lpszClassName    =3D szAppName;
    wnd.lpszMenuName    =3D NULL;
    wnd.style        =3D CS_HREDRAW | CS_VREDRAW;
   =20
    <SPAN class=3Dcpp-keyword>if</SPAN> (!RegisterClass(&amp;wnd))
    {
        MessageBox(NULL, <SPAN class=3Dcpp-string>"Can not register =
window class"</SPAN>, <SPAN class=3Dcpp-string>"Error"</SPAN>,=20
                   MB_OK | MB_ICONINFORMATION);
        <SPAN class=3Dcpp-keyword>return</SPAN> -<SPAN =
class=3Dcpp-literal>1</SPAN>;
    }
   =20
    hWnd =3D CreateWindow(szAppName, <SPAN class=3Dcpp-string>"Hello =
world"</SPAN>, WS_OVERLAPPEDWINDOW, CW_USEDEFAULT,=20
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, =
hInstance, NULL);
   =20
    ShowWindow(hWnd, nCmdShow);
    UpdateWindow(hWnd);
   =20
    <SPAN class=3Dcpp-keyword>while</SPAN> (GetMessage(&amp;msg, NULL, =
<SPAN class=3Dcpp-literal>0</SPAN>, <SPAN class=3Dcpp-literal>0</SPAN>))
    {
        DispatchMessage(&amp;msg);
    }
   =20
    <SPAN class=3Dcpp-keyword>return</SPAN> msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM =
lParam)
{
    HDC hDC;
    PAINTSTRUCT ps;
    RECT rect;

    <SPAN class=3Dcpp-keyword>switch</SPAN> (uMsg)
    {
    <SPAN class=3Dcpp-keyword>case</SPAN> WM_PAINT:
        hDC =3D BeginPaint(hWnd, &amp;ps);
        GetClientRect(hWnd, &amp;rect);
        DrawText(hDC, <SPAN class=3Dcpp-string>"Hello world"</SPAN>, =
-<SPAN class=3Dcpp-literal>1</SPAN>, &amp;rect, DT_SINGLELINE | =
DT_CENTER | DT_VCENTER);
        EndPaint(hWnd, &amp;ps);
        <SPAN class=3Dcpp-keyword>break</SPAN>;

    <SPAN class=3Dcpp-keyword>case</SPAN> WM_DESTROY:
        PostQuitMessage(<SPAN class=3Dcpp-literal>0</SPAN>);
        <SPAN class=3Dcpp-keyword>break</SPAN>;
    }
   =20
    <SPAN class=3Dcpp-keyword>return</SPAN> DefWindowProc(hWnd, uMsg, =
wParam, lParam);
}
</PRE>
      <P>There is nothing new in this program. This program just =
displays a=20
      window and display Hello world at center of this. </P>ATL is =
object=20
      oriented library, means you are using classes to do your work. =
Let's try=20
      to do the same thing ourselves and make some small classes to make =
our=20
      work easier. Ok we are going to make some classes for our work, =
but what=20
      would be the criteria for making classes? In other words how many =
classes=20
      are should make, what are their relationship, method and =
properties. I am=20
      not planning to discuss the whole object oriented theory and the =
process=20
      here to make quality library. To make my task similar I make group =
of=20
      related API's and put those related API in one class. I put all =
the API's,=20
      which deals with window in one class and it can be repeated to =
other type=20
      of API's like for font, file, menu etc. So I made a small class =
and put=20
      the entire API's whose first parameter is <CODE>HWND</CODE> in =
that class.=20
      This class is nothing more than a thing wrapper on the Windows =
API's. My=20
      class Name is <CODE>ZWindow</CODE>, you are free to choose =
whatever name=20
      you like. This class is something like this. <PRE><SPAN =
class=3Dcpp-keyword>class</SPAN> ZWindow
{
<SPAN class=3Dcpp-keyword>public</SPAN>:
    HWND m_hWnd;

    ZWindow(HWND hWnd =3D <SPAN class=3Dcpp-literal>0</SPAN>) : =
m_hWnd(hWnd) { }

    <SPAN class=3Dcpp-keyword>inline</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> Attach(HWND hWnd)
    { m_hWnd =3D hWnd; }

    <SPAN class=3Dcpp-keyword>inline</SPAN> BOOL ShowWindow(<SPAN =
class=3Dcpp-keyword>int</SPAN> nCmdShow)
    { <SPAN class=3Dcpp-keyword>return</SPAN> ::ShowWindow(m_hWnd, =
nCmdShow); }

    <SPAN class=3Dcpp-keyword>inline</SPAN> BOOL UpdateWindow()
    {  <SPAN class=3Dcpp-keyword>return</SPAN> ::UpdateWindow(m_hWnd); }

};
</PRE>
      <P>Here I put only those API's which are required at the moment. =
You may=20
      add all the API's in this class. The only advantage of this class =
is that=20
      now you don't have to pass the <CODE>HWND</CODE> parameter for =
windowing=20
      API's, this class will pass that parameter itself. </P>
      <P>Well nothing special till now. But what about our Window =
CallBack=20
      function? Remember the first parameter of that call back function =
is also=20
      <CODE>HWND</CODE>, so it should be member of this class according =
to our=20
      criteria. So I add our callback function in this class too. Now =
this class=20
      should be something like this. </P><PRE><SPAN =
class=3Dcpp-keyword>class</SPAN> ZWindow
{
<SPAN class=3Dcpp-keyword>public</SPAN>:
    HWND m_hWnd;

    ZWindow(HWND hWnd =3D <SPAN class=3Dcpp-literal>0</SPAN>) : =
m_hWnd(hWnd) { }

    <SPAN class=3Dcpp-keyword>inline</SPAN> <SPAN =
class=3Dcpp-keyword>void</SPAN> Attach(HWND hWnd)
    { m_hWnd =3D hWnd; }

    <SPAN class=3Dcpp-keyword>inline</SPAN> BOOL ShowWindow(<SPAN =
class=3Dcpp-keyword>int</SPAN> nCmdShow)
    { <SPAN class=3Dcpp-keyword>return</SPAN> ::ShowWindow(m_hWnd, =
nCmdShow); }

    <SPAN class=3Dcpp-keyword>inline</SPAN> BOOL UpdateWindow()
    {  <SPAN class=3Dcpp-keyword>return</SPAN> ::UpdateWindow(m_hWnd); }

    LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM =