问题描述:

I'm using this code GlobalKeyboardHook.cs to hook keyboard.

I've altered everything specified as per instructions in this post. Now My code looks like this:

using System;

using System.Collections.Generic;

using System.Text;

using System.Runtime.InteropServices;

using System.Windows.Forms;

namespace Utilities

{

/// <summary>

/// A class that manages a global low level keyboard hook

/// </summary>

class globalKeyboardHook

{

#region Constant, Structure and Delegate Definitions

/// <summary>

/// defines the callback type for the hook

/// </summary>

public delegate int keyboardHookProc(int code, int wParam, ref keyboardHookStruct lParam);

public struct keyboardHookStruct

{

public int vkCode;

public int scanCode;

public int flags;

public int time;

public int dwExtraInfo;

}

const int WH_KEYBOARD_LL = 13;

const int WM_KEYDOWN = 0x100;

const int WM_KEYUP = 0x101;

const int WM_SYSKEYDOWN = 0x104;

const int WM_SYSKEYUP = 0x105;

private static keyboardHookProc callbackDelegate;

#endregion

#region Instance Variables

/// <summary>

/// The collections of keys to watch for

/// </summary>

public List<Keys> HookedKeys = new List<Keys>();

/// <summary>

/// Handle to the hook, need this to unhook and call the next hook

/// </summary>

IntPtr hhook = IntPtr.Zero;

#endregion

#region Events

/// <summary>

/// Occurs when one of the hooked keys is pressed

/// </summary>

public event KeyEventHandler KeyDown;

/// <summary>

/// Occurs when one of the hooked keys is released

/// </summary>

public event KeyEventHandler KeyUp;

#endregion

#region Constructors and Destructors

/// <summary>

/// Initializes a new instance of the <see cref="globalKeyboardHook"/> class and installs the keyboard hook.

/// </summary>

public globalKeyboardHook()

{

hook();

}

/// <summary>

/// Releases unmanaged resources and performs other cleanup operations before the

/// <see cref="globalKeyboardHook"/> is reclaimed by garbage collection and uninstalls the keyboard hook.

/// </summary>

~globalKeyboardHook()

{

unhook();

}

#endregion

#region Public Methods

/// <summary>

/// Installs the global hook

/// </summary>

public void hook()

{

IntPtr hInstance = LoadLibrary("User32");

callbackDelegate = new keyboardHookProc(hookProc);

hhook = SetWindowsHookEx(WH_KEYBOARD_LL, hookProc, hInstance, 0);

if (hhook == IntPtr.Zero) throw new System.ComponentModel.Win32Exception();

}

/// <summary>

/// Uninstalls the global hook

/// </summary>

public void unhook()

{

bool ok = UnhookWindowsHookEx(hhook);

if (!ok) throw new System.ComponentModel.Win32Exception();

callbackDelegate = null;

}

/// <summary>

/// The callback for the keyboard hook

/// </summary>

/// <param name="code">The hook code, if it isn't >= 0, the function shouldn't do anyting</param>

/// <param name="wParam">The event type</param>

/// <param name="lParam">The keyhook event information</param>

/// <returns></returns>

public int hookProc(int code, int wParam, ref keyboardHookStruct lParam)

{

if (code >= 0)

{

Keys key = (Keys)lParam.vkCode;

if (HookedKeys.Contains(key))

{

KeyEventArgs kea = new KeyEventArgs(key);

if ((wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) && (KeyDown != null))

{

KeyDown(this, kea);

}

else if ((wParam == WM_KEYUP || wParam == WM_SYSKEYUP) && (KeyUp != null))

{

KeyUp(this, kea);

}

if (kea.Handled)

return 1;

}

}

return CallNextHookEx(hhook, code, wParam, ref lParam);

}

#endregion

#region DLL imports

/// <summary>

/// Sets the windows hook, do the desired event, one of hInstance or threadId must be non-null

/// </summary>

/// <param name="idHook">The id of the event you want to hook</param>

/// <param name="callback">The callback.</param>

/// <param name="hInstance">The handle you want to attach the event to, can be null</param>

/// <param name="threadId">The thread you want to attach the event to, can be null</param>

/// <returns>a handle to the desired hook</returns>

[DllImport("user32.dll")]

static extern IntPtr SetWindowsHookEx(int idHook, keyboardHookProc callback, IntPtr hInstance, uint threadId);

/// <summary>

/// Unhooks the windows hook.

/// </summary>

/// <param name="hInstance">The hook handle that was returned from SetWindowsHookEx</param>

/// <returns>True if successful, false otherwise</returns>

[DllImport("user32.dll")]

static extern bool UnhookWindowsHookEx(IntPtr hInstance);

/// <summary>

/// Calls the next hook.

/// </summary>

/// <param name="idHook">The hook id</param>

/// <param name="nCode">The hook code</param>

/// <param name="wParam">The wparam.</param>

/// <param name="lParam">The lparam.</param>

/// <returns></returns>

[DllImport("user32.dll")]

static extern int CallNextHookEx(IntPtr idHook, int nCode, int wParam, ref keyboardHookStruct lParam);

/// <summary>

/// Loads the library.

/// </summary>

/// <param name="lpFileName">Name of the library</param>

/// <returns>A handle to the library</returns>

[DllImport("kernel32.dll")]

static extern IntPtr LoadLibrary(string lpFileName);

#endregion

}

}

This function in my program hooks UP & DOWN keys when my program window is visible. It unhook those keys when visibility changes.

private void AutoCompleteMenu_VisibleChanged(object sender, EventArgs e)

{

if (this.Visible == true)

{

if (hookFlag == 0)

{

try

{

gkh.hook();

gkh.HookedKeys.Add(Keys.Up);

gkh.HookedKeys.Add(Keys.Down);

gkh.KeyDown += new KeyEventHandler(gkh_KeyDown);

gkh.KeyUp += new KeyEventHandler(gkh_KeyUp);

}

catch (Exception)

{

MessageBox.Show("Cannot hook arrow keys! Please use mouse keys to select a word");

}

hookFlag = 1;

}

}

else

{

if (hookFlag == 1)

{

hookFlag = 0;

gkh.unhook();

}

}

}

This code is written on program initialization part: globalKeyboardHook gkh = new globalKeyboardHook();

Still I'm getting this error whenever my program try to hook keys:

CallbackOnCollectedDelegate was detected Message: A callback was made

on a garbage collected delegate of type

'CaretPosition!Utilities.globalKeyboardHook+keyboardHookProc::Invoke'.

This may cause application crashes, corruption and data loss. When

passing delegates to unmanaged code, they must be kept alive by the

managed application until it is guaranteed that they will never be

called.

please help me to solve this problem.

网友答案:

It may happen, that Garbage collection doesn't occure at all, and when you close the application it results in hook on an invalid delegate (since the application is unloaded).

You should not use finalizer ~globalKeyboardHook to free system resources other than allocated memory, but IDisposable instead and unhook explicitly. Or you may unhook on

AppDomain.CurrentDomain.ProcessExit

event

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