windows程式設計讀書筆記3——字元顯示2

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由於顯示的字元可能會不全，我們很容易想到的一個解決辦法是使用捲軸。

先看一下代碼，再進行分析：

/*----------------------------------------------------   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) ;}

我們在CreateWindow函數的第三個參數加上 WS_VSCROLL 即垂直捲軸。

同時在WM_CREATE中加入：

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

SetScrollRange設定捲軸範圍，NUMLINES是在標頭檔中定義的行數，

捲軸的每個位置對應一行文字。

iVscrollPos變數記錄這滑塊的當前位置。

在滑鼠拖動滑塊時，會產生WM_VSCROLL訊息，對iVscrollPos變數進行賦值操作。

還有更改的一處是Y座標： y = cyChar * (i - iVscrollPos) ; 這保證了滑動之後，小於當前位置的字元不會輸出到螢幕（因為他們Y座標是負的）

同時在滑動捲軸的時候：

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

當捲軸位置改變之後我們會用InvalidateRect函數使視窗無效，會產生WM_PAINT訊息，重繪視窗。

windows程式設計讀書筆記3——字元顯示2