Creating a Sample Application
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8/28/2008
This topic contains a code example that creates a simple Windows Embedded CE–based application. This sample application demonstrates the basic framework that is common to all Windows Embedded CE–based applications. It begins executing with the WinMain function, which performs the following tasks:
- WinMain places the application-instance handle in a global variable. Because this handle is used in various places throughout an application, it is common to place it in a global variable that is accessible to all functions. The smallest possible interval that a timer can measure is the system-tick interval.
- WinMain calls the application-defined InitApplication function, which then calls the RegisterClass function to register the main window class of the application. More complicated applications might need to register more window classes and determine if other instances of the application are running.
- WinMain calls the application-defined InitInstance function, which then calls the CreateWindow function to create a window. CreateWindow returns a window handle identifying the new window. This handle is used in subsequent function calls to refer to the window.
- WinMain creates the message loop by calling the GetMessage function, TranslateMessage, and DispatchMessage functions in the format that is displayed in the sample application. This loop receives messages and dispatches them to the window procedures.
Note that the application does not call the MainWndProc window procedure directly. The system calls this function as the message loop receives and dispatches messages. In this application, MainWndProc processes only the WM_CLOSE message that instructs the window to close. When the window receives a WM_CLOSE message, it calls the PostQuitMessage function, which then calls GetMessage to return FALSE. This return value, in turn, causes the message loop to terminate and the application to exit.
Windows Embedded CE sends many other messages to the window besides WM_CLOSE. MainWndProc passes all other messages to the DefWindowProc function, which is the default window procedure that is provided by the system. Pass all of the messages that the application does not process itself to DefWindowProc; otherwise, your window might not function correctly. The following code example shows a framework for creating a Windows Embedded CE–based application.
#include <windows.h>
HINSTANCE g_hInst = NULL; // Handle to the application instance
HWND g_hwndMain = NULL; // Handle to the application main window
TCHAR g_szTitle[80] = TEXT ("Main Window"),
// Application main window name
g_szClassName[80] = TEXT ("Main window class");
// Main window class name
/***********************************************************************
FUNCTION:
WndProc
PURPOSE:
The callback function for the main window. It processes messages that
are sent to the main window.
***********************************************************************/
LRESULT CALLBACK WndProc (HWND hwnd, UINT umsg, WPARAM wParam,
LPARAM lParam)
{
switch (umsg)
{
// Add cases such as WM_CREATE, WM_COMMAND, WM_PAINT if you don't
// want to pass these messages along for default processing.
case WM_CLOSE:
DestroyWindow (hwnd);
return 0;
case WM_DESTROY:
PostQuitMessage (0);
return 0;
}
return DefWindowProc (hwnd, umsg, wParam, lParam);
}
/***********************************************************************
FUNCTION:
InitInstance
PURPOSE:
Create and display the main window.
***********************************************************************/
BOOL InitInstance (HINSTANCE hInstance, int iCmdShow)
{
g_hInst = hInstance;
g_hwndMain = CreateWindow (
g_szClassName, // Registered class name
g_szTitle, // Application window name
WS_OVERLAPPED, // Window style
CW_USEDEFAULT, // Horizontal position of the window
CW_USEDEFAULT, // Vertical position of the window
CW_USEDEFAULT, // Window width
CW_USEDEFAULT, // Window height
NULL, // Handle to the parent window
NULL, // Handle to the menu the identifier
hInstance, // Handle to the application instance
NULL); // Pointer to the window-creation data
// If it failed to create the window, return FALSE.
if (!g_hwndMain)
return FALSE;
ShowWindow (g_hwndMain, iCmdShow);
UpdateWindow (g_hwndMain);
return TRUE;
}
/***********************************************************************
FUNCTION:
InitApplication
PURPOSE:
Declare the window class structure, assign values to the window class
structure members, and register the window class.
***********************************************************************/
BOOL InitApplication (HINSTANCE hInstance)
{
WNDCLASS wndclass;
wndclass.style = CS_HREDRAW | CS_VREDRAW;
wndclass.lpfnWndProc = (WNDPROC)WndProc;
wndclass.cbClsExtra = 0;
wndclass.cbWndExtra = 0;
wndclass.hIcon = NULL;
wndclass.hInstance = hInstance;
wndclass.hCursor = NULL;
wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH);
wndclass.lpszMenuName = NULL;
wndclass.lpszClassName = g_szClassName;
return RegisterClass (&wndclass);
}
/***********************************************************************
FUNCTION:
WinMain
PURPOSE:
The WinMain function of the application. It is called by the system as
the initial entry point for this Windows Embedded CE-based application.
***********************************************************************/
int WINAPI WinMain (
HINSTANCE hInstance, // Handle to the current instance
HINSTANCE hPrevInstance, // Handle to the previous instance
LPWSTR lpCmdLine, // Pointer to the command line
int iCmdShow) // Shows the state of the window
{
MSG msg; // Message structure
HACCEL hAccel; // Handle of the accelerator
// table
// Use this code to prevent your application from starting twice
// assuming that your application has not changed its window text
if (FindWindow(g_szClassName, g_szTitle)){
SetForegroundWindow(FindWindow(g_szClassName, g_szTitle));
return FALSE;
}
if (!hPrevInstance)
{
if (!InitApplication (hInstance))
return FALSE;
}
if (!InitInstance (hInstance, iCmdShow))
return FALSE;
// Insert code here to load the accelerator table.
// hAccel = LoadAccelerators (...);
while (GetMessage (&msg, NULL, 0, 0))
{
if (!TranslateAccelerator (
g_hwndMain, // Handle to the destination window
hAccel, // Handle to the accelerator table
&msg)) // Address of the message data
{
TranslateMessage (&msg);
DispatchMessage (&msg);
}
}
return msg.wParam;
}
See Also
Concepts
Working with Windows and Messages