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。