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windows程序设计读书笔记3——字符显示2

由于显示的字符可能会不全,我们很容易想到的一个解决办法是使用滚动条。

先看一下代码,再进行分析:

/*----------------------------------------------------   SYSMETS2.C -- System Metrics Display Program No. 2                 (c) Charles Petzold, 1998  ----------------------------------------------------*/#define WINVER 0x0500#include <windows.h>#include "sysmets.h" LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,                    PSTR szCmdLine, int iCmdShow){     static TCHAR szAppName[] = TEXT ("SysMets2") ;     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) GetStockObject (WHITE_BRUSH) ;     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 ("Get System Metrics No. 2"),                          WS_OVERLAPPEDWINDOW | WS_VSCROLL ,                          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 int  cxChar, cxCaps, cyChar, cyClient, iVscrollPos ;     HDC         hdc ;     int         i, y ;     PAINTSTRUCT ps ;     TCHAR       szBuffer[10] ;     TEXTMETRIC  tm ;     switch (message)     {     case WM_CREATE:          hdc = GetDC (hwnd) ;          GetTextMetrics (hdc, &tm) ;          cxChar = tm.tmAveCharWidth ;          cxCaps = (tm.tmPitchAndFamily & 1 ? 3 : 2) * cxChar / 2 ;          cyChar = tm.tmHeight + tm.tmExternalLeading ;          ReleaseDC (hwnd, hdc) ;          SetScrollRange (hwnd, SB_VERT, 0, NUMLINES - 1, FALSE) ;          SetScrollPos   (hwnd, SB_VERT, iVscrollPos, TRUE) ;          return 0 ;     case WM_SIZE:          cyClient = HIWORD (lParam) ;          return 0 ;     case WM_VSCROLL:          switch (LOWORD (wParam))          {          case SB_LINEUP:               iVscrollPos -= 1 ;               break ;               case SB_LINEDOWN:               iVscrollPos += 1 ;               break ;               case SB_PAGEUP:               iVscrollPos -= cyClient / cyChar ;               break ;               case SB_PAGEDOWN:               iVscrollPos += cyClient / cyChar ;               break ;               case SB_THUMBPOSITION:               iVscrollPos = HIWORD (wParam) ;               break ;               default :               break ;          }          iVscrollPos = max (0, min (iVscrollPos, NUMLINES - 1)) ;          if (iVscrollPos != GetScrollPos (hwnd, SB_VERT))          {               SetScrollPos (hwnd, SB_VERT, iVscrollPos, TRUE) ;               InvalidateRect (hwnd, NULL, TRUE) ;          }          return 0 ;     case WM_PAINT:          hdc = BeginPaint (hwnd, &ps) ;               for (i = 0 ; i < NUMLINES ; i++)          {               y = cyChar * (i - iVscrollPos) ;                    TextOut (hdc, 0, y,                        sysmetrics[i].szLabel,                        lstrlen (sysmetrics[i].szLabel)) ;                    TextOut (hdc, 22 * cxCaps, y,                        sysmetrics[i].szDesc,                        lstrlen (sysmetrics[i].szDesc)) ;                    SetTextAlign (hdc, TA_RIGHT | TA_TOP) ;                    TextOut (hdc, 22 * cxCaps + 40 * cxChar, y, szBuffer,                        wsprintf (szBuffer, TEXT ("%5d"),                             GetSystemMetrics (sysmetrics[i].iIndex))) ;                    SetTextAlign (hdc, TA_LEFT | TA_TOP) ;          }          EndPaint (hwnd, &ps) ;          return 0 ;     case WM_DESTROY:          PostQuitMessage (0) ;          return 0 ;     }     return DefWindowProc (hwnd, message, wParam, lParam) ;}

我们在CreateWindow函数的第三个参数加上 WS_VSCROLL 即垂直滚动条。

同时在WM_CREATE中加入:

SetScrollRange (hwnd, SB_VERT, 0, NUMLINES - 1, FALSE) ;SetScrollPos   (hwnd, SB_VERT, iVscrollPos, TRUE) ;

SetScrollRange设置滚动条范围,NUMLINES是在头文件中定义的行数,

滚动条的每个位置对应一行文字。

iVscrollPos变量记录这滑块的当前位置。

在鼠标拖动滑块时,会产生WM_VSCROLL消息,对iVscrollPos变量进行赋值操作。

还有更改的一处是Y坐标: y = cyChar * (i - iVscrollPos) ; 这保证了滑动之后,小于当前位置的字符不会输出到屏幕(因为他们Y坐标是负的)

同时在滑动滚动条的时候:

if (iVscrollPos != GetScrollPos (hwnd, SB_VERT))          {               SetScrollPos (hwnd, SB_VERT, iVscrollPos, TRUE) ;               InvalidateRect (hwnd, NULL, TRUE) ;          }

当滚动条位置改变之后我们会用InvalidateRect函数使窗口无效,会生成WM_PAINT消息,重绘窗口。

windows程序设计读书笔记3——字符显示2