Thursday, February 5, 2009

C# Key Listener

CodeGuru has this post:

Hi All

Looking for a little help..

I would like to create a process that runs on both a Windows XP and Vista Machines that loads on startup, what this process will do is, on the "F12" keypress it brings up a simple form that a user fills in some details then clicks on send, then it goes back to sleep and waits on the "F12" key being pressed.

Never created a process before so any help is appreciated.



This post will describe how to do this in C#. We will approach this by creating an executable that could be loaded at startup. It will listen for the F12 keyboard event and present a message box.

Create a new C# Console project in Visual Studio, call it 'ListenForHotkey.'

We will use a windows hook to notify our application when a key is pressed. So in the Program.cs file you should define four win32 API's. SetWindowsHookEx, UnhookWindowsHookEx, GetModuleName, CallNextHookEx. We'll also define a delegate for the callback, and some constants.

Here is the Program.cs with these definitions.
using System;
using System.Runtime.InteropServices; //Used for dll import
using System.Diagnostics; //'Process'

namespace ListenForHotkey
static class Program
static void Main()
// Define win32 api calls.
[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr SetWindowsHookEx(int idHook, LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool UnhookWindowsHookEx(IntPtr hhk);

[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr GetModuleHandle(string lpModuleName);

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode,
IntPtr wParam, IntPtr lParam);

//Define delegate for the callback.
private delegate IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);

//Define constants
private const int WH_KEYBOARD_LL = 13;


In the code above we've defined a delegate called LowLevelKeyboardProc that is the signature of the callback. Let's add our callback.

// Callback, executed when hook is triggered. In our case on keydown.            
private static IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
System.Console.WriteLine("key pressed");

//Call next hook in chain.
return CallNextHookEx(m_hookId, nCode, wParam, lParam);


Our callback simply prints that a key was pressed then calls the next hook if applicable. This is important else another application that register a hook may not be called.

Lastly we should register our hook, and run the app. This is done in the main method.

static void Main()
using (Process curProcess = Process.GetCurrentProcess())
using (ProcessModule curModule = curProcess.MainModule)

m_hookId = SetWindowsHookEx(WH_KEYBOARD_LL, HookCallback, GetModuleHandle(curModule.ModuleName), 0);

In main we register the callback then call Application.Run() which puts the app in an infinite loop by waiting for any system messages. When the program is ready to exit we unregister our hook.

That's it.

Hope it helps.

GWT Programming Concepts

GWT Programming Concepts

This tutorial will introduce the architecture of GWT. It is aimed at programmers with little or no Java experience, but with reasonable experience with other programming languages using object oriented programming.

GWT is a single application. It consists of a series of panels. There may be a single panel onto which other panels are places, or multiple panels. You create and place Widgets onto these panels. Widgets are items like hyperlinks, textbox's, buttons, etc. With each of these widgets you can attach event listeners that will be execute when appropriate. For example you can attach a click listener to a button and when the user clicks the button, the action will be performed.

The important part of GWT is that panels and widgets are added using Java code.
Each widget (which includes a Panel) is an object that is derived from a number of base classes. For example:

UIObject : the base class with properties or methods:

* Size
* Width
* toString

Widget : derived from UIObject (so has its properties and methods), extended by:

* attached
* parent

FocusWidget : derived from Widget (so has its properties and methods), extended by:

* ClickListenerCollection
* addClickListener

Button : derived from FocusWidget (so has its properties and methods), extended by:

* getHTML
* setHTML

So through a series of inherited commands, the Panel object is instructed by GWT to deliver its HTML. Before delivering its own html, it instructs its children objects to deliver their html. Before their delivery, they also ask their children. And so on, until there are no unpolled children. In this way, the panel's html incorporates all the required html for all of its children.

So as a programmer, all you need to do is to slap down some panels, add some widgets containing the text, buttons, menu items, response to button clicks etc that you want and save it.

The command to "compile" the program takes all the Java objects you have created in your code, pulls out the required html and programmed actions and creates a final html container with a large amount of Javascript that writes the html you instructed through your Java objects.

far more functional and much more fun.