要实现一个屏幕键盘，需要监听所有键盘事件，无论窗体是否被激活。因此需要一个全局的钩子，也就
是系统范围的钩子。
什么是钩子（Hook）
钩子（Hook）是Windows提供的一种消息处理机制平台，是指在程序正常运行中接受信息之前预先
启动的函数，用来检查和修改传给该程序的信息，（钩子）实际上是一个处理消息的程序段，通
过系统调用，把它挂入系统。每当特定的消息发出，在没有到达目的窗口前，钩子程序就先捕获
该消息，亦即钩子函数先得到控制权。这时钩子函数即可以加工处理（改变）该消息，也可以不
作处理而继续传递该消息，还可以强制结束消息的传递。注意：安装钩子函数将会影响系统的性
能。监测“系统范围事件”的系统钩子特别明显。因为系统在处理所有的相关事件时都将调用您的
钩子函数，这样您的系统将会明显的减慢。所以应谨慎使用，用完后立即卸载。还有，由于您可
以预先截获其它进程的消息，所以一旦您的钩子函数出了问题的话必将影响其它的进程。
钩子的作用范围
一共有两种范围（类型）的钩子，局部的和远程的。局部钩子仅钩挂自己进程的事件。远程的钩
子还可以将钩挂其它进程发生的事件。远程的钩子又有两种： 基于线程的钩子将捕获其它进程中
某一特定线程的事件。简言之，就是可以用来观察其它进程中的某一特定线程将发生的事件。 系
统范围的钩子将捕捉系统中所有进程将发生的事件消息。
Hook 类型
Windows共有14种Hooks，每一种类型的Hook可以使应用程序能够监视不同类型的系统消息处理机
制。下面描述所有可以利用的Hook类型的发生时机。详细内容可以查阅MSDN，这里只介绍我们将要
用到的两种类型的钩子。
（1）WH_KEYBOARD_LL Hook
WH_KEYBOARD_LL Hook监视输入到线程消息队列中的键盘消息。
（2）WH_MOUSE_LL Hook
WH_MOUSE_LL Hook监视输入到线程消息队列中的鼠标消息。
下面的 class 把 API 调用封装起来以便调用。
1
// NativeMethods.cs
2
using System;
3
using System.Runtime.InteropServices;
4
using System.Drawing;
5
6
namespace CnBlogs.Youzai.ScreenKeyboard
{
7
[StructLayout(LayoutKind.Sequential)]
8
internal struct MOUSEINPUT
{
9
public int dx;
10
public int dy;
11
public int mouseData;
12
public int dwFlags;
13
public int time;
14
public IntPtr dwExtraInfo;
15
}
16
17
[StructLayout(LayoutKind.Sequential)]
18
internal struct KEYBDINPUT
{
19
public short wVk;
20
public short wScan;
21
public int dwFlags;
22
public int time;
23
public IntPtr dwExtraInfo;
24
}
25
26
[StructLayout(LayoutKind.Explicit)]
27
internal struct Input
{
28
[FieldOffset(0)]
29
public int type;
30
[FieldOffset(4)]
31
public MOUSEINPUT mi;
32
[FieldOffset(4)]
33
public KEYBDINPUT ki;
34
[FieldOffset(4)]
35
public HARDWAREINPUT hi;
36
}
37
38
[StructLayout(LayoutKind.Sequential)]
39
internal struct HARDWAREINPUT
{
40
public int uMsg;
41
public short wParamL;
42
public short wParamH;
43
}
44
45
internal class INPUT
{
46
public const int MOUSE = 0;
47
public const int KEYBOARD = 1;
48
public const int HARDWARE = 2;
49
}
50
51
internal static class NativeMethods
{
52
[DllImport("User32.dll", CharSet = CharSet.Auto, SetLastError = false)]
53
internal static extern IntPtr GetWindowLong(IntPtr hWnd, int nIndex);
54
55
[DllImport("User32.dll", CharSet = CharSet.Auto, SetLastError = false)]
56
internal static extern IntPtr SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);
57
58
[DllImport("User32.dll", EntryPoint = "SendInput", CharSet = CharSet.Auto)]
59
internal static extern UInt32 SendInput(UInt32 nInputs, Input[] pInputs, Int32 cbSize);
60
61
[DllImport("Kernel32.dll", EntryPoint = "GetTickCount", CharSet = CharSet.Auto)]
62
internal static extern int GetTickCount();
63
64
[DllImport("User32.dll", EntryPoint = "GetKeyState", CharSet = CharSet.Auto)]
65
internal static extern short GetKeyState(int nVirtKey);
66
67
[DllImport("User32.dll", EntryPoint = "SendMessage", CharSet = CharSet.Auto)]
68
internal static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam);
69
}
70
}
安装钩子
使用SetWindowsHookEx函数（API函数），指定一个Hook类型、自己的Hook过程是全局还是局部Hook，
同时给出Hook过程的进入点，就可以轻松的安装自己的Hook过程。SetWindowsHookEx总是将你的Hook函
数放置在Hook链的顶端。你可以使用CallNextHookEx函数将系统消息传递给Hook链中的下一个函数。
对于某些类型的Hook，系统将向该类的所有Hook函数发送消息，这时，
Hook函数中的CallNextHookEx语句将被忽略。全局（远程钩子）Hook函数可以拦截系统中所有线程的某
个特定的消息，为了安装一个全局Hook过程，必须在应用程序外建立一个DLL并将该Hook函数封装到其中，
应用程序在安装全局Hook过程时必须先得到该DLL模块的句柄。将Dll名传递给LoadLibrary 函数，就会得
到该DLL模块的句柄；得到该句柄 后，使用GetProcAddress函数可以得到Hook过程的地址。最后，使用
SetWindowsHookEx将 Hook过程的首址嵌入相应的Hook链中，SetWindowsHookEx传递一个模块句柄，它为
Hook过程的进入点，线程标识符置为0，该Hook过程同系统中的所有线程关联。如果是安装局部Hook此时
该Hook函数可以放置在DLL中，也可以放置在应用程序的模块段。在C#中通过平台调用（前文已经介绍过）
来调用API函数。
1
public void Start( bool installMouseHook, bool installKeyboardHook)
{
2
if (hMouseHook == IntPtr.Zero && installMouseHook)
{
3
MouseHookProcedure = new HookProc(MouseHookProc);
4
hMouseHook = SetWindowsHookEx(
5
WH_MOUSE_LL,
6
MouseHookProcedure,
7
Marshal.GetHINSTANCE(
8
Assembly.GetExecutingAssembly().GetModules()[0]),
9
10
);
11
12
if (hMouseHook == IntPtr.Zero)
{
13
int errorCode = Marshal.GetLastWin32Error();
14
Stop(true, false, false);
15
16
throw new Win32Exception(errorCode);
17
}
18
}
19
20
if (hKeyboardHook == IntPtr.Zero && installKeyboardHook)
{
21
KeyboardHookProcedure = new HookProc(KeyboardHookProc);
22
//install hook
23
hKeyboardHook = SetWindowsHookEx(
24
WH_KEYBOARD_LL,
25
KeyboardHookProcedure,
26
Marshal.GetHINSTANCE(
27
Assembly.GetExecutingAssembly().GetModules()[0]),
28
0);
29
// If SetWindowsHookEx fails.
30
if (hKeyboardHook == IntPtr.Zero)
{
31
// Returns the error code returned by the last
32
// unmanaged function called using platform invoke
33
// that has the DllImportAttribute.SetLastError flag set.
34
int errorCode = Marshal.GetLastWin32Error();
35
//do cleanup
36
Stop(false, true, false);
37
//Initializes and throws a new instance of the
38
// Win32Exception class with the specified error.
39
throw new Win32Exception(errorCode);
40
}
41
}
42
}
使用完钩子后，要进行卸载，这个可以写在析构函数中。
1
2
public void Stop()
{
3
this.Stop(true, true, true);
4
}
5
6
public void Stop( bool uninstallMouseHook, bool uninstallKeyboardHook,
7
bool throwExceptions)
{
8
// if mouse hook set and must be uninstalled
9
if (hMouseHook != IntPtr.Zero && uninstallMouseHook)
{
10
// uninstall hook
11
bool retMouse = UnhookWindowsHookEx(hMouseHook);
12
// reset invalid handle
13
hMouseHook = IntPtr.Zero;
14
// if failed and exception must be thrown
15
if (retMouse == false && throwExceptions)
{
16
// Returns the error code returned by the last unmanaged function
17
// called using platform invoke that has the DllImportAttribute.
18
// SetLastError flag set.
19
int errorCode = Marshal.GetLastWin32Error();
20
// Initializes and throws a new instance of the Win32Exception class
21
// with the specified error.
22
throw new Win32Exception(errorCode);
23
}
24
}
25
26
// if keyboard hook set and must be uninstalled
27
if (hKeyboardHook != IntPtr.Zero && uninstallKeyboardHook)
{
28
// uninstall hook
29
bool retKeyboard = UnhookWindowsHookEx(hKeyboardHook);
30
// reset invalid handle
31
hKeyboardHook = IntPtr.Zero;
32
// if failed and exception must be thrown
33
if (retKeyboard == false && throwExceptions)
{
34
// Returns the error code returned by the last unmanaged function
35
// called using platform invoke that has the DllImportAttribute.
36
// SetLastError flag set.
37
int errorCode = Marshal.GetLastWin32Error();
38
// Initializes and throws a new instance of the Win32Exception class
39
// with the specified error.
40
throw new Win32Exception(errorCode);
41
}
42
}
43
}
44
将这个文件编译成一个dll，即可在应用程序中调用。通过它提供的事件，便可监听所有的键盘事件。
但是，这只能监听键盘事件，没有键盘的情况下，怎么会有键盘事件？其实很简单，通过SendInput
API函数提供虚拟键盘代码的调用即可模拟键盘输入。下面的代码模拟一个 KeyDown 和 KeyUp 过程，
把他们连接起来就是一次按键过程。
1
private void SendKeyDown( short key)
{
2
Input[] input = new Input[1];
3
input[0].type = INPUT.KEYBOARD;
4
input[0].ki.wVk = key;
5
input[0].ki.time = NativeMethods.GetTickCount();
6
7
if (NativeMethods.SendInput((uint)input.Length, input, Marshal.SizeOf(input[0]))
8
< input.Length)
{
9
throw new Win32Exception(Marshal.GetLastWin32Error());
10
}
11
}
12
13
private void SendKeyUp( short key)
{
14
Input[] input = new Input[1];
15
input[0].type = INPUT.KEYBOARD;
16
input[0].ki.wVk = key;
17
input[0].ki.dwFlags = KeyboardConstaint.KEYEVENTF_KEYUP;
18
input[0].ki.time = NativeMethods.GetTickCount();
19
20
if (NativeMethods.SendInput((uint)input.Length, input, Marshal.SizeOf(input[0]))
21
< input.Length)
{
22
throw new Win32Exception(Marshal.GetLastWin32Error());
23
}
24
}
自己实现一个 KeyBoardButton 控件用作按钮，用 Visual Studio 或者 SharpDevelop 为屏幕键盘设计 UI，然后
在这些 Button 的 Click 事件里面模拟一个按键过程。
1
2
private void ButtonOnClick( object sender, EventArgs e)
{
3
KeyboardButton btnKey = sender as KeyboardButton;
4
if (btnKey == null)
{
5
return;
6
}
7
8
SendKeyCommand(btnKey);
9
}
10
11
private void SendKeyCommand(KeyboardButton keyButton)
{
12
short key = keyButton.VKCode;
13
if (combinationVKButtonsMap.ContainsKey(key))
{
14
if (keyButton.Checked)
{
15
SendKeyUp(key);
16
} else
{
17
SendKeyDown(key);
18
}
19
} else
{
20
SendKeyDown(key);
21
SendKeyUp(key);
22
}
23
}
其中 combinationVKButtonsMap 是一个 IDictionary<short, IList<KeyboardButton>>, key 存储的是
VK_SHIFT, VK_CONTROL 等组合键的键盘码。左右两个按钮对应同一个键盘码，因此需要放在一个 List 里。
标准键盘上的每一个键都有虚拟键码( VK_CODE)与之对应。还有一些其他的常量，
把它写在一个静态 class 里吧。
1
// KeyboardConstaint.cs
2
internal static class KeyboardConstaint
{
3
internal static readonly short VK_F1 = 0x70;
4
internal static readonly short VK_F2 = 0x71;
5
internal static readonly short VK_F3 = 0x72;
6
internal static readonly short VK_F4 = 0x73;
7
internal static readonly short VK_F5 = 0x74;
8
internal static readonly short VK_F6 = 0x75;
9
internal static readonly short VK_F7 = 0x76;
10
internal static readonly short VK_F8 = 0x77;
11
internal static readonly short VK_F9 = 0x78;
12
internal static readonly short VK_F10 = 0x79;
13
internal static readonly short VK_F11 = 0x7A;
14
internal static readonly short VK_F12 = 0x7B;
15
16
internal static readonly short VK_LEFT = 0x25;
17
internal static readonly short VK_UP = 0x26;
18
internal static readonly short VK_RIGHT = 0x27;
19
internal static readonly short VK_DOWN = 0x28;
20
21
internal static readonly short VK_NONE = 0x00;
22
internal static readonly short VK_ESCAPE = 0x1B;
23
internal static readonly short VK_EXECUTE = 0x2B;
24
internal static readonly short VK_CANCEL = 0x03;
25
internal static readonly short VK_RETURN = 0x0D;
26
internal static readonly short VK_ACCEPT = 0x1E;
27
internal static readonly short VK_BACK = 0x08;
28
internal static readonly short VK_TAB = 0x09;
29
internal static readonly short VK_DELETE = 0x2E;
30
internal static readonly short VK_CAPITAL = 0x14;
31
internal static readonly short VK_NUMLOCK = 0x90;
32
internal static readonly short VK_SPACE = 0x20;
33
internal static readonly short VK_DECIMAL = 0x6E;
34
internal static readonly short VK_SUBTRACT = 0x6D;
35
36
internal static readonly short VK_ADD = 0x6B;
37
internal static readonly short VK_DIVIDE = 0x6F;
38
internal static readonly short VK_MULTIPLY = 0x6A;
39
internal static readonly short VK_INSERT = 0x2D;
40
41
internal static readonly short VK_OEM_1 = 0xBA; // ';:' for US
42
internal static readonly short VK_OEM_PLUS = 0xBB; // '+' any country
43
44
internal static readonly short VK_OEM_MINUS = 0xBD; // '-' any country
45
46
internal static readonly short VK_OEM_2 = 0xBF; // '/?' for US
47
internal static readonly short VK_OEM_3 = 0xC0; // '`~' for US
48
internal static readonly short VK_OEM_4 = 0xDB; // '[{' for US
49
internal static readonly short VK_OEM_5 = 0xDC; // '\|' for US
50
internal static readonly short VK_OEM_6 = 0xDD; // ']}' for US
51
internal static readonly short VK_OEM_7 = 0xDE; // ''"' for US
52
internal static readonly short VK_OEM_PERIOD = 0xBE; // '.>' any country
53
internal static readonly short VK_OEM_COMMA = 0xBC; // ',<' any country
54
internal static readonly short VK_SHIFT = 0x10;
55
internal static readonly short VK_CONTROL = 0x11;
56
internal static readonly short VK_MENU = 0x12;
57
internal static readonly short VK_LWIN = 0x5B;
58
internal static readonly short VK_RWIN = 0x5C;
59
internal static readonly short VK_APPS = 0x5D;
60
61
internal static readonly short VK_LSHIFT = 0xA0;
62
internal static readonly short VK_RSHIFT = 0xA1;
63
internal static readonly short VK_LCONTROL = 0xA2;
64
internal static readonly short VK_RCONTROL = 0xA3;
65
internal static readonly short VK_LMENU = 0xA4;
66
internal static readonly short VK_RMENU = 0xA5;
67
68
internal static readonly short VK_SNAPSHOT = 0x2C;
69
internal static readonly short VK_SCROLL = 0x91;
70
internal static readonly short VK_PAUSE = 0x13;
71
internal static readonly short VK_HOME = 0x24;
72
73
internal static readonly short VK_NEXT = 0x22;
74
internal static readonly short VK_PRIOR = 0x21;
75
internal static readonly short VK_END = 0x23;
76
77
internal static readonly short VK_NUMPAD0 = 0x60;
78
internal static readonly short VK_NUMPAD1 = 0x61;
79
internal static readonly short VK_NUMPAD2 = 0x62;
80
internal static readonly short VK_NUMPAD3 = 0x63;
81
internal static readonly short VK_NUMPAD4 = 0x64;
82
internal static readonly short VK_NUMPAD5 = 0x65;
83
internal static readonly short VK_NUMPAD5NOTHING = 0x0C;
84
internal static readonly short VK_NUMPAD6 = 0x66;
85
internal static readonly short VK_NUMPAD7 = 0x67;
86
internal static readonly short VK_NUMPAD8 = 0x68;
87
internal static readonly short VK_NUMPAD9 = 0x69;
88
89
internal static readonly short KEYEVENTF_EXTENDEDKEY = 0x0001;
90
internal static readonly short KEYEVENTF_KEYUP = 0x0002;
91
92
internal static readonly int GWL_EXSTYLE = -20;
93
internal static readonly int WS_DISABLED = 0X8000000;
94
internal static readonly int WM_SETFOCUS = 0X0007;
95
}
屏幕键盘必须是一个不能获得输入焦点的窗体，在这个窗体的构造函数里，可以安装
一个全局鼠标钩子，再通过调用 SetWindowLong API 函数完成。
1
UserActivityHook hook = new UserActivityHook( true , true );
2
hook.MouseActivity += HookOnMouseActivity;
3
4
private void HookOnMouseActivity( object sener, HookEx.MouseExEventArgs e)
{
5
Point location = e.Location;
6
7
if (e.Button == MouseButtons.Left)
{
8
Rectangle captionRect = new Rectangle(this.Location, new Size(this.Width,
9
SystemInformation.CaptionHeight));
10
if (captionRect.Contains(location))
{
11
NativeMethods.SetWindowLong(this.Handle, KeyboardConstaint.GWL_EXSTYLE,
12
(int)NativeMethods.GetWindowLong(this.Handle, KeyboardConstaint.GWL_EXSTYLE)
13
& (~KeyboardConstaint.WS_DISABLED));
14
NativeMethods.SendMessage(this.Handle, KeyboardConstaint.WM_SETFOCUS, IntPtr.Zero, IntPtr.Zero);
15
} else
{
16
NativeMethods.SetWindowLong(this.Handle, KeyboardConstaint.GWL_EXSTYLE,
17
(int)NativeMethods.GetWindowLong(this.Handle, KeyboardConstaint.GWL_EXSTYLE) |
18
KeyboardConstaint.WS_DISABLED);
19
}
20
}
21
}
鼠标单击标题栏，让屏幕键盘可以接收焦点，并激活，单击其他部分则不激活窗体（如果激活了，其他程序必然取消激活，
输入就无法进行了），这样才可以进行输入，并且保证了可以拖动窗体到其他位置。
至此，一个屏幕键盘程序差不多完成了，能够实现与实际键盘完全同步。至于窗体，按键重绘，以及 Num Lock, Caps Lock,
Scroll Lock 等键盘灯的模拟，这里就不讲了，如果有兴趣，可以下载完整的代码。最后我们的屏幕键盘程序运行的效果如
下图:
点击下载完整源代码
说明：本程序参考了 Jeffrey Richter 先生的著作 CLR via C#, Second Edition, MSDN 以及一些网络资料。
转载于:https://www.cnblogs.com/youzai/archive/2008/05/19/1202732.html