UNIX中有一个著名的实用程序叫做head，它显示文件开始的几行。让我们使用清单方块为Windows编写一个类似的程序。如程序9-6所示，HEAD将所有文件和子目录列在清单方块中。您可以挑选某个被选择的文件来显示，方法是在该文件上使用鼠标双击或者使用Enter键按下要选的文件。您也可以使用这两种方法之一来改变子目录。这个程序在HEAD窗口显示区域的右边，从文件的开头开始显示，它最多能够显示8 KB的内容。
程序9-6 HEAD
HEAD.C /*------------------------------------------------------------------------- HEAD.C -- Displays beginning (head) of file (c) Charles Petzold, 1998 --------------------------------------------------------------------------*/ #include <windows.h> #define ID_LIST 1 #define ID_TEXT 2 #define MAXREAD 8192 #define DIRATTR (DDL_READWRITE | DDL_READONLY | DDL_HIDDEN | DDL_SYSTEM | \ DDL_DIRECTORY | DDL_ARCHIVE | DDL_DRIVES) #define DTFLAGS (DT_WORDBREAK | DT_EXPANDTABS | DT_NOCLIP |DT_NOPREFIX) LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ; LRESULT CALLBACK ListProc (HWND, UINT, WPARAM, LPARAM) ; WNDPROC OldList ; int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow) { static TCHAR szAppName[] = TEXT ("head") ; HWND hwnd ; MSG msg ; WNDCLASS wndclass ; wndclass.style = CS_HREDRAW | CS_VREDRAW ; wndclass.lpfnWndProc = WndProc ; wndclass.cbClsExtra = 0 ; wndclass.cbWndExtra = 0 ; wndclass.hInstance = hInstance ; wndclass.hIcon = LoadIcon (NULL, IDI_APPLICATION) ; wndclass.hCursor = LoadCursor (NULL, IDC_ARROW) ; wndclass.hbrBackground = (HBRUSH) (COLOR_BTNFACE + 1) ; wndclass.lpszMenuName = NULL ; wndclass.lpszClassName = szAppName ; if (!RegisterClass (&wndclass)) { MessageBox ( NULL, TEXT ("This program requires Windows NT!"), szAppName, MB_ICONERROR) ; return 0 ; } hwnd = CreateWindow (szAppName, TEXT ("head"), WS_OVERLAPPEDWINDOW | WS_CLIPCHILDREN, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, hInstance, NULL) ; ShowWindow (hwnd, iCmdShow) ; UpdateWindow (hwnd) ; while (GetMessage (&msg, NULL, 0, 0)) { TranslateMessage (&msg) ; DispatchMessage (&msg) ; } return msg.wParam ; } LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam,LPARAM lParam) { static BOOL bValidFile ; static BYTE buffer[MAXREAD] ; static HWND hwndList, hwndText ; static RECT rect ; static TCHAR szFile[MAX_PATH + 1] ; HANDLE hFile ; HDC hdc ; int i, cxChar, cyChar ; PAINTSTRUCT ps ; TCHAR szBuffer[MAX_PATH + 1] ; switch (message) { case WM_CREATE : cxChar = LOWORD (GetDialogBaseUnits ()) ; cyChar = HIWORD (GetDialogBaseUnits ()) ; rect.left = 20 * cxChar ; rect.top = 3 * cyChar ; hwndList = CreateWindow (TEXT ("listbox"), NULL, WS_CHILDWINDOW | WS_VISIBLE | LBS_STANDARD, cxChar, cyChar * 3, cxChar * 13 + GetSystemMetrics (SM_CXVSCROLL), cyChar * 10, hwnd, (HMENU) ID_LIST, (HINSTANCE) GetWindowLong (hwnd, GWL_HINSTANCE), NULL) ; GetCurrentDirectory (MAX_PATH + 1, szBuffer) ; hwndText = CreateWindow (TEXT ("static"), szBuffer, WS_CHILDWINDOW | WS_VISIBLE | SS_LEFT, cxChar, cyChar, cxChar * MAX_PATH, cyChar, hwnd, (HMENU) ID_TEXT, (HINSTANCE) GetWindowLong (hwnd, GWL_HINSTANCE), NULL) ; OldList = (WNDPROC) SetWindowLong (hwndList, GWL_WNDPROC, (LPARAM) ListProc) ; SendMessage (hwndList, LB_DIR, DIRATTR, (LPARAM) TEXT ("*.*")) ; return 0 ; caseWM_SIZE : rect.right = LOWORD (lParam) ; rect.bottom = HIWORD (lParam) ; return 0 ; case WM_SETFOCUS : SetFocus (hwndList) ; return 0 ; case WM_COMMAND : if (LOWORD (wParam) == ID_LIST && HIWORD (wParam) == LBN_DBLCLK) { if (LB_ERR == (i = SendMessage (hwndList, LB_GETCURSEL, 0, 0))) break ; SendMessage (hwndList, LB_GETTEXT, i, (LPARAM) szBuffer) ; if (INVALID_HANDLE_VALUE != (hFile = CreateFile (szBuffer, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, 0, NULL))) { CloseHandle (hFile) ; bValidFile = TRUE ; lstrcpy (szFile, szBuffer) ; GetCurrentDirectory (MAX_PATH + 1, szBuffer) ; if (szBuffer [lstrlen (szBuffer) - 1] != '\\') lstrcat (szBuffer, TEXT ("\\")) ; SetWindowText (hwndText, lstrcat (szBuffer, szFile)) ; } else { bValidFile = FALSE ; szBuffer [lstrlen (szBuffer) - 1] = '\0' ; // If setting the directory doesn't work, maybe it's // a drive change, so try that. if (!SetCurrentDirectory (szBuffer + 1)) { szBuffer [3] = ':' ; szBuffer [4] = '\0' ; SetCurrentDirectory (szBuffer + 2) ; } // Get the new directory name and fill the list box. GetCurrentDirectory (MAX_PATH + 1, szBuffer) ; SetWindowText (hwndText, szBuffer) ; SendMessage (hwndList, LB_RESETCONTENT, 0, 0) ; SendMessage (hwndList, LB_DIR, DIRATTR, (LPARAM) TEXT ("*.*")) ; } InvalidateRect (hwnd, NULL, TRUE) ; } return 0 ; case WM_PAINT : if (!bValidFile) break ; if (INVALID_HANDLE_VALUE == (hFile = CreateFile (szFile, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, 0, NULL))) { bValidFile = FALSE ; break ; } ReadFile (hFile, buffer, MAXREAD, &i, NULL) ; CloseHandle (hFile) ; // i now equals the number of bytes in buffer. // Commence getting a device context for displaying text. hdc = BeginPaint (hwnd, &ps) ; SelectObject (hdc, GetStockObject (SYSTEM_FIXED_FONT)) ; SetTextColor (hdc, GetSysColor (COLOR_BTNTEXT)) ; SetBkColor (hdc, GetSysColor (COLOR_BTNFACE)) ; // Assume the file is ASCII DrawTextA (hdc, buffer, i, &rect, DTFLAGS) ; EndPaint (hwnd, &ps) ; return 0 ; case WM_DESTROY : PostQuitMessage (0) ; return 0 ; } return DefWindowProc (hwnd, message, wParam, lParam) ; } LRESULT CALLBACK ListProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) { if (message == WM_KEYDOWN && wParam == VK_RETURN) SendMessage (GetParent (hwnd), WM_COMMAND, MAKELONG (1, LBN_DBLCLK), (LPARAM) hwnd) ; return CallWindowProc (OldList, hwnd, message, wParam, lParam) ; }