二、Windows按键消息—为SYSMETS加上键盘处理功能
在编写第四章中三个版本的SYSMETS程序时，我们还不了解键盘，只能使用滚动条和鼠标来卷动文字。现在我们知道了处理键盘消息的方法，那么不妨在程序中加入键盘接口。显然，这是处理光标移动键的工作。我们将大多数光标键（Home、End、Page Up、Page Down、Up Arrow和Down Arrow）用于垂直卷动，左箭头键和右箭头键用于不太重要的水平卷动。
建立键盘接口的一种简单方法是在窗口消息处理程序中加入与WM_VSCROLL和WM_HSCROLL处理方式相仿，而且本质上相同的WM_KEYDOWN处理方法。不过这样子做是不聪明的，因为如果要修改滚动条的做法，就必须相对应地修改WM_KEYDOWN。
为什么不简单地将每一种WM_KEYDOWN消息都翻译成同等效用的WM_VSCROLL或者WM_HSCROLL消息呢？通过向窗口消息处理程序发送假冒消息，我们可能会让WndProc认为它获得了卷动信息。
在Windows中，这种方法是可行的。发送消息的函数叫做SendMessage，它所用的参数与传递到窗口消息处理程序的参数是相同的：
SendMessage (hwnd, message, wParam, lParam) ;
在呼叫SendMessage时，Windows呼叫窗口句柄为hwnd的窗口消息处理程序，并把这四个参数传给它。当窗口消息处理程序完成消息处理之后，Windows把控制传回到SendMessage呼叫之后的下一道叙述。您发送消息过去的窗口消息处理程序，可以是同一个窗口消息处理程序、同一程序中的其它窗口消息处理程序或者其它应用程序，中的窗口消息处理程序。
下面说明在SYSMETS程序中使用SendMessage处理WM_KEYDOWN代码的方法：
caseWM_KEYDOWN:
switch (wParam)
{
case VK_HOME:
SendMessage (hwnd, WM_VSCROLL, SB_TOP, 0) ;
break ;
case VK_END:
SendMessage (hwnd, WM_VSCROLL, SB_BOTTOM, 0) ;
break ;
case VK_PRIOR:
SendMessage (hwnd, WM_VSCROLL, SB_PAGEUP, 0) ;
break ;
至此，您已经有了大概观念了吧。我们的目标是为滚动条添加键盘接口，并且也正在这么做。通过把卷动消息发送到窗口消息处理程序，我们实作了用光标移动键进行卷动列的功能。现在您知道在SYSMETS3中为WM_VSCROLL消息加上SB_TOP和SB_BOTTOM处理码的原因了吧。在那里并没有用到它，但是现在处理Home和End键时就有用了。如程序6-1所示的SYSENTS4就加上了这些变化。编译这个程序时还需要用到第四章的SYSMETS.H文件。
程序6-1 SYSMETS4
SYSMETS4.C
/*----------------------------------------------------------------------
SYSMETS4.C -- System Metrics Display Program No. 4
(c) Charles Petzold, 1998
------------------------------------------------------------------------*/
#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 ("SysMets4") ;
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 ("Program requires Windows NT!"),
szAppName, MB_ICONERROR) ;
return 0 ;
}
hwnd = CreateWindow (szAppName, TEXT ("Get System Metrics No. 4"),
WS_OVERLAPPEDWINDOW | WS_VSCROLL | WS_HSCROLL,
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, cxClient, cyClient, iMaxWidth ;
HDC hdc ;
int i, x, y, iVertPos, iHorzPos, iPaintBeg, iPaintEnd ;
PAINTSTRUCT ps ;
SCROLLINFO si ;
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) ;
// Save the width of the three columns
iMaxWidth = 40 * cxChar + 22 * cxCaps ;
return 0 ;
case WM_SIZE:
cxClient = LOWORD (lParam) ;
cyClient = HIWORD (lParam) ;
// Set vertical scroll bar range and page size
si.cbSize = sizeof (si) ;
si.fMask = SIF_RANGE | SIF_PAGE ;
si.nMin = 0 ;
si.nMax = NUMLINES - 1 ;
si.nPage = cyClient / cyChar ;
SetScrollInfo (hwnd, SB_VERT, &si, TRUE) ;
// Set horizontal scroll bar range and page size
si.cbSize = sizeof (si) ;
si.fMask = SIF_RANGE | SIF_PAGE ;
si.nMin = 0 ;
si.nMax = 2 + iMaxWidth / cxChar ;
si.nPage = cxClient / cxChar ;
SetScrollInfo (hwnd, SB_HORZ, &si, TRUE) ;
return 0 ;
case WM_VSCROLL:
// Get all the vertical scroll bar information
si.cbSize = sizeof (si) ;
si.fMask = SIF_ALL ;
GetScrollInfo (hwnd, SB_VERT, &si) ;
// Save the position for comparison later on
iVertPos = si.nPos ;
switch (LOWORD (wParam))
{
case SB_TOP:
si.nPos = si.nMin ;
break ;
case SB_BOTTOM:
si.nPos = si.nMax ;
break ;
case SB_LINEUP:
si.nPos -= 1 ;
break ;
case SB_LINEDOWN:
si.nPos += 1 ;
break ;
case SB_PAGEUP:
si.nPos -= si.nPage ;
break ;
case SB_PAGEDOWN:
si.nPos += si.nPage ;
break ;
case SB_THUMBTRACK:
si.nPos = si.nTrackPos ;
break ;
default:
break ;
}
// Set the position and then retrieve it. Due to adjustments
// by Windows it might not be the same as the value set.
si.fMask = SIF_POS ;
SetScrollInfo (hwnd, SB_VERT, &si, TRUE) ;
GetScrollInfo (hwnd, SB_VERT, &si) ;
// If the position has changed, scroll the window and update it
if (si.nPos != iVertPos)
{
ScrollWindow (hwnd, 0, cyChar * (iVertPos - si.nPos),
NULL, NULL) ;
UpdateWindow (hwnd) ;
}
return 0 ;
case WM_HSCROLL:
// Get all the vertical scroll bar information
si.cbSize = sizeof (si) ;
si.fMask = SIF_ALL ;
// Save the position for comparison later on
GetScrollInfo (hwnd, SB_HORZ, &si) ;
iHorzPos = si.nPos ;
switch (LOWORD (wParam))
{
case SB_LINELEFT:
si.nPos -= 1 ;
break ;
case SB_LINERIGHT:
si.nPos += 1 ;
break ;
case SB_PAGELEFT:
si.nPos -= si.nPage ;
break ;
case SB_PAGERIGHT:
si.nPos += si.nPage ;
break ;
case SB_THUMBPOSITION:
si.nPos = si.nTrackPos ;
break ;
default:
break ;
}
// Set the position and then retrieve it. Due to adjustments
// by Windows it might not be the same as the value set.
si.fMask = SIF_POS ;
SetScrollInfo (hwnd, SB_HORZ, &si, TRUE) ;
GetScrollInfo (hwnd, SB_HORZ, &si) ;
// If the position has changed, scroll the window
if (si.nPos != iHorzPos)
{
ScrollWindow (hwnd, cxChar * (iHorzPos - si.nPos), 0,
NULL, NULL) ;
}
return 0 ;
case WM_KEYDOWN:
switch (wParam)
{
case VK_HOME:
SendMessage (hwnd, WM_VSCROLL, SB_TOP, 0) ;
break ;
case VK_END:
SendMessage (hwnd, WM_VSCROLL, SB_BOTTOM, 0) ;
break ;
case VK_PRIOR:
SendMessage (hwnd, WM_VSCROLL, SB_PAGEUP, 0) ;
break ;
case VK_NEXT:
SendMessage (hwnd, WM_VSCROLL, SB_PAGEDOWN, 0) ;
break ;
case VK_UP:
SendMessage (hwnd, WM_VSCROLL, SB_LINEUP, 0) ;
break ;
case VK_DOWN:
SendMessage (hwnd, WM_VSCROLL, SB_LINEDOWN, 0) ;
break ;
case VK_LEFT:
SendMessage (hwnd, WM_HSCROLL, SB_PAGEUP, 0) ;
break ;
case VK_RIGHT:
SendMessage (hwnd, WM_HSCROLL, SB_PAGEDOWN, 0) ;
break ;
}
return 0 ;
case WM_PAINT:
hdc = BeginPaint (hwnd, &ps) ;
// Get vertical scroll bar position
si.cbSize = sizeof (si) ;
si.fMask = SIF_POS ;
GetScrollInfo (hwnd, SB_VERT, &si) ;
iVertPos = si.nPos ;
// Get horizontal scroll bar position
GetScrollInfo (hwnd, SB_HORZ, &si) ;
iHorzPos = si.nPos ;
// Find painting limits
iPaintBeg = max (0, iVertPos + ps.rcPaint.top / cyChar) ;
iPaintEnd = min (NUMLINES - 1,
iVertPos + ps.rcPaint.bottom / cyChar) ;
for (i = iPaintBeg ; i <= iPaintEnd ; i++)
{
x = cxChar * (1 - iHorzPos) ;
y = cyChar * (i - iVertPos) ;
TextOut (hdc, x, y,
sysmetrics[i].szLabel,
lstrlen (sysmetrics[i].szLabel)) ;
TextOut (hdc, x + 22 * cxCaps, y,
sysmetrics[i].szDesc,
lstrlen (sysmetrics[i].szDesc)) ;
SetTextAlign (hdc, TA_RIGHT | TA_TOP) ;
TextOut (hdc, x + 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) ;
}
