Processing Global Mouse and Keyboard Hooks in C#

原文：http://www.codeproject.com/KB/cs/globalhook.aspx

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Introduction

This class allows you to tap keyboard and mouse and/or to detect their activity even when an application runs in the background or does not have any user interface at all. This class raises common .NET events with

KeyEventArgs

and

MouseEventArgs

, so you can easily retrieve any information you need.

Background

There are a number of applications that run in the background and detect user inactivity to change their mode. For example, MSN Messenger (or any other messenger). I was going to write such an application, so I searched MSDN and found "exactly" what I needed: 318804 - HOW TO: Set a Windows Hook in Visual C# .NET. This article describes how to tap the mouse movement, but it works only when an application is active. At the end of this article, I found this explanation: "Global hook is not supported in .NET Framework. You cannot implement global hooks in Microsoft .NET Framework...". Anyway, I continued my research and found out that there are exceptions. There are

WH_KEYBOARD_LL

and

WH_MOUSE_LL

hooks that can be installed globally. So, I have basically replaced

WH_MOUSE

with

WH_MOUSE_LL

in the MSDN example, and it works.

The second step was to extract the information received into a .NET

EventArgs

and raise the appropriate events.

I found a similar article in CodeProject, under Global System Hooks in .NET by Michael Kennedy, but what I dislike is, there is an unmanaged DLL in C++ that is a main part of this solution. This unmanaged DLL is in C++, and a number of classes make it complicated to integrate it in my own tiny application.

Using the code

To use this class in your application, you need just to create an instance of it and hang on events you would like to process. Hooks are automatically installed when the object is created, but you can stop and start listening using appropriate public methods.

UserActivityHook actHook;
void MainFormLoad(object sender, System.EventArgs e)
{
actHook= new UserActivityHook(); // crate an instance
// hang on events
actHook.OnMouseActivity+=new MouseEventHandler(MouseMoved);
actHook.KeyDown+=new KeyEventHandler(MyKeyDown);
actHook.KeyPress+=new KeyPressEventHandler(MyKeyPress);
actHook.KeyUp+=new KeyEventHandler(MyKeyUp);
}

Now, an example of how to process an event:

public void MouseMoved(object sender, MouseEventArgs e)
{
labelMousePosition.Text=String.Format("x={0}  y={1}", e.X, e.Y);
if (e.Clicks>0) LogWrite("MouseButton     - " + e.Button.ToString());
}

Changes and updates in the new version

I'd like to thank you all for all the useful comments in the discussion forum. There were a lot of bugs and proposals posted after this article was published on 4 Jun 2004. Over and over again came the same topics, and I had to refer to previous posts in the discussion, that is why I have decided to revise the code and publish a FAQ. Here is the list of the most important changes:

The project was converted into Visual Studio 2005

The problem with upper case characters is solved

Mouse wheel information is now included in event arguments

Better exception handling

Cancellation of keyboard events using the

Handled

property of event arguments

XML documentation of functions

FAQ

Question:

The project cannot be run in Visual Studio .NET 2005 in debug mode because of an exception error caused by calling the

SetWindowsHookEx

. Why? Is it a problem of .NET 2.0?

Answer:

The compiled release version works well so that can not be a .NET 2.0 problem. To workaround, you just need to uncheck the check box in the project properties that says: "Enable Visual Studio hosting process". In the menu: Project -> Project Properties... -> Debug -> Enable the Visual Studio hosting process.

Question:

I need to suppress some keystrokes after I have processed them.

Answer:

Just set the

e.Handled

property to

true

in the key events you have processed. It prevent the keystrokes being processed by other applications.

Question:

Is it possible to convert your global hooks to application hooks which capture keystrokes and mouse movements only within the application?

Answer:

Yes. Just use:

private const int WH_MOUSE = 7;
private const int WH_KEYBOARD = 2;

everywhere, instead of:

private const int WH_MOUSE_LL = 14;
private const int WH_KEYBOARD_LL = 13;

Question:

Does it work on Win98 (Windows ME, Windows 95)?

Answer:

Yes and No. The global hooks

WH_MOUSE_LL

and

WH_KEYBOARD_LL

can be monitored only under Windows NT/2000/XP. In other cases, you can only use application hooks (

WH_MOUSE and WH_KEYBOARD

) which capture keystrokes and mouse movement only within the application.

Question:

I have a long delay when closing applications using hooks by clicking the x button in the titlebar. If I close the application via another event (button click) for example, that works fine.

Answer:

It's a know bug of Microsoft. It has to do with the Windows themes. If you disable the Windows themes, the problem goes away. Another choice is to have the hook code run in a secondary thread.

Question:

How do I catch key combinations like Ctrl+Shift+A?

Answer:

You'll have to track which keys have gone down but not up. Only the most recently pressed key keeps sending

KeyDown

messages, but the others will still send a

KeyUp

when released. So if you make three flags

IsCtrlDown

,

IsShiftDown

, and

IsADown

, and set them to

true

at

KeyDown

and

false

at

KeyUp

, the expression

(IsCtrlDown && IsShiftDown && IsADown)

will give you the required result.

Question:

Does it works with .NET Framework 1.1 and Visual Studio 2003?

Answer:

Yes. The file UserActivityHook.cs can be used without any changes, in a VS2003 .NET 1.1 project.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)