Declare Function SetWindowsHookEx Lib "user32" Alias "SetWindowsHookExA" _
(ByVal idHook As Long, _
ByVal lpfn As Long, _
ByVal hmod As Long, _
ByVal dwThreadId As Long) As Long
idHook代表是何种Hook,有以下几种
Public Const WH_CALLWNDPROC = 4
Public Const WH_CALLWNDPROCRET = 12
Public Const WH_CBT = 5
Public Const WH_DEBUG = 9
Public Const WH_FOREGROUNDIDLE = 11
Public Const WH_GETMESSAGE = 3
Public Const WH_HARDWARE = 8
Public Const WH_JOURNALPLAYBACK = 1
Public Const WH_JOURNALRECORD = 0
Public Const WH_KEYBOARD = 2
Public Const WH_MOUSE = 7
Public Const WH_MSGFILTER = (-1)
Public Const WH_SHELL = 10
Public Const WH_SYSMSGFILTER = 6
Declare Function CallNextHookEx Lib "user32" Alias "CallNextHookEx" _
(ByVal hHook As Long, _
ByVal ncode As Long, _
ByVal wParam As Long, _
lParam As Any) As Long
Public Sub UnHookKBD()
If hnexthookproc <> 0 Then
UnhookWindowsHookEx hHook
hHook = 0
End If
End Sub
Public Function EnableKBDHook()
If hHook <> 0 Then
Exit Function
End If
hhook = SetWindowsHookEx(WH_KEYBOARD, AddressOf _
MyKBHFunc, App.hInstance, App.ThreadId)
End Function
Public Function MyKBHFunc(ByVal iCode As Long, _
ByVal wParam As Long, ByVal lParam As Long) As Long
MyKBHfunc = 0 '表示要处理这个讯息
If wParam = vbKeySnapshot Then '侦测 有没有按到PrintScreen键
MyKBHFunc = 1 '在这个Hook便吃掉这个讯息
End If
Call CallNextHookEx(hHook, iCode, wParam, lParam) '传给下一个Hook
End Function
至於其他的 Hook的详细资料与nCode,wParam, lParam的意义,请查Win32 Help
或Windows 95: A Developer's Guide (Jeffrey Richter着)(中译本:
基峰 李书良译 侯俊杰总监 Windows95程式设计指南)
SUMMARY
F1CDHELP is a file in the Microsoft Software Library that demonstrates how an application can implement context sensitive help for the dialog boxes provided by the dynamic-link library (DLL) COMMDLG.DLL (the common dialog box DLL). When the user presses the F1 key, the application calls Windows Help.
The recommended user interface for an application to provide access to Windows Help is through the F1 key. This article describes a technique that can be used with the common dialog box DLL to bring up context sensitive help for each dialog box. The sample uses the SetWindowsHookEx() function to set a task-specific keyboard hook, which monitors keyboard input and responds to the F1 key.
Because this application uses a task-specific hook, the hook function code resides in the application's .EXE file and is not required to be in a fixed code page in a DLL. (The filter function for each system- wide hook must be in a DLL.)
MORE INFORMATION
The following files are available for download from the Microsoft Download Center. Click the file names below to download the files:
F1CDHelp.exe
For more information about how to download files from the Microsoft Download Center, please visit the Download Center at the following Web address
http://www.microsoft.com/downloads/search.asp
and then click How to use the Microsoft Download Center.
The technique used in this article is straightforward and minimizes the number of global variables required. The application installs the keyboard hook and calls the RegisterWindowMessage() function to define a help message. When an application registers the help message, the common dialog box DLL notifies the application each time the user chooses the Help button in one of the common dialog boxes. The DLL sends the help message to the window procedure of the dialog box's parent window.
When the keyboard hook function detects that the F1 key is pressed, it posts a WM_COMMAND message to the appropriate window procedure. In the F1CDHELP example, the message is posted either to the main window (when no dialog box is displayed) or to the dialog box's window procedure. If the message is posted to one of the common dialog boxes, wParam is set to pshHelp; the application simulates choosing the Help button in the common dialog box. Otherwise, wParam is set to IDM_HELPCONTENTS; the application simulates selecting a menu item in the application.
The following code demonstrates installing the hook and registering the help message in response to a WM_CREATE message:
// Register the help message. The common dialog box DLL sends this
// message when the user chooses the Help file in a common
// dialog box.
gwHelpMsg = RegisterWindowMessage((LPSTR)HELPMSGSTRING);
break;
The following code demonstrates removing the keyboard hook in response to a WM_DESTROY message:
case WM_DESTROY:
UnhookWindowsHookEx(ghKbrdHook);
break;
The hook function receives notification about the F1 key and posts a message as appropriate:
// If this is a repeat or the key is being released, ignore it.
if (lParam & 0x80000000 || lParam & 0x40000000)
return CallNextHookEx(ghKbrdHook, iCode, wParam, lParam);
else
{
if (IsWindowEnabled(ghWnd)) // F1 pressed in main window?
PostMessage(ghWnd, WM_COMMAND, IDM_HELPCONTENTS, 0L);
else // F1 pressed in a dialog box
PostMessage(GetActiveWindow(), WM_COMMAND, pshHelp, 0L);
}
return CallNextHookEx(ghKbrdHook, iCode, wParam, lParam);
}
The second PostMessage() call above is executed when the user requests help in a specific common dialog box. This simulates choosing the Help button in the dialog box. Because the application registered the help message (during the processing of its WM_CREATE message), the common dialog box DLL will send the gwHelpMessage to the parent window procedure. An application can process this message as follows:
default:
if (message == gwHelpMsg) // Help requested in a common dialog
// box
{
// The lParam points to an OPENFILENAME or a CHOOSECOLOR data
// structure. The application can differentiate between them by
// checking the structure's size, which is in the first four
// bytes (a DWORD) of the structure. This allows the application
// to display different help for each of the common dialog boxes.
dwStructSize = (DWORD)(*(LPDWORD)lParam);
switch (dwStructSize)
{
case sizeof(OPENFILENAME):
MessageBox((HWND)wParam, "Help requested for OpenFile",
gszAppName, MB_OK);
break;
case sizeof(CHOOSECOLOR):
MessageBox((HWND)wParam, "Help requested for ChooseColor"
gszAppName, MB_OK);
break;
default:
break;
}
break;
}
else // Not a help message
return DefWindowProc(hWnd, message, wParam, lParam);
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