C#

public class MainForm : Form
{
   private Button button = new Button("Hai");
   private Label label = new Label();

   private void InitializeComponent()
   {
       button.Click += new ClickHandler(MainForm_buttonClick);
   }

   private void MainForm_ButtonClick(object sender, EventArgs e)
   {
       label.Text = "Bye";
   }
}

<br />
using System;<br />
using System.Text;<br />
using System.Runtime.InteropServices;<br />
using System.Diagnostics;<br />
<br />
namespace APPLoginWindow<br />
{<br />
	/// <summary><br />
	/// Summary description for Class1.<br />
	/// </summary><br />
	public class APPLogin<br />
	{<br />
<br />
		private object data;<br />
<br />
		#region Contructor, dispose, main<br />
		public APPLogin()<br />
		{<br />
			getAPPLogin();<br />
		}<br />
		#endregion<br />
<br />
		#region win32 imports<br />
		public delegate bool EnumWindowsCallback(int hwnd, int lParam);<br />
		public delegate bool EnumThreadProc(IntPtr hWnd, IntPtr lParam);<br />
<br />
		[DllImport("User32.dll")] public static extern int GetWindowText(int hwnd,StringBuilder lpString, uint bufferSize);<br />
		 <br />
		[DllImport("User32.dll")] public static extern int EnumWindows (EnumWindowsCallback callback, int lParam);<br />
		[DllImport("User32.dll")] public static extern int EnumChildWindows (int hWndParent, EnumWindowsCallback callback, int lParam);<br />
		[DllImport("User32.dll")] public static extern bool EnumThreadWindows (uint threadId, EnumThreadProc pfnEnum, IntPtr lParam);<br />
<br />
		[DllImport("User32.dll")] public static extern int RealGetWindowClass(int hWnd,StringBuilder pszType,uint bufferSize);<br />
		[DllImport("User32.dll")] public static extern int SendMessage( int hwnd, int uMsg, int wParam, [MarshalAs(System.Runtime.InteropServices.UnmanagedType.LPStr)] string lParam);<br />
		<br />
		[DllImport("User32.dll") ] public static extern int FindWindow (string lpClassName,string WindowName);<br />
		[DllImport("User32.dll") ] public static extern int FindWindowEx (int hWnd,int hWnd2,string lpsz,string lpsz2);<br />
		[DllImport("User32.dll") ] public static extern int SetWindowText(int hWnd,string lpsz);<br />
		#endregion<br />
<br />
		#region Constants + fields<br />
		public static int GW_HWNDNEXT = 2;<br />
		public static int GW_CHILD = 5;<br />
		public static int GW_OWNER = 4;<br />
		public static int GWL_HWNDPARENT = -8;<br />
		public static int WM_SETTEXT =  12;<br />
		public const int HWND_MESSAGE = -3;<br />
		public const int BM_CLICK = 0x00F5; //Clicking a button<br />
		public const int WM_CHAR = 258;<br />
		private string _windowText = "";<br />
		#endregion<br />
<br />
		#region Callback functions for listing windows<br />
		private bool displayAPPLogin(int hWnd, int lParam)<br />
		{<br />
			StringBuilder windowName = new StringBuilder(255);<br />
			StringBuilder className  = new StringBuilder(255);<br />
<br />
			GetWindowText(hWnd, windowName, 255);<br />
			RealGetWindowClass(hWnd,className,255);<br />
			if ( windowName.ToString().ToLower().IndexOf("<Name of Login Window>") != -1 )<br />
			{<br />
				data = hWnd;<br />
			}<br />
<br />
			return true;<br />
		}<br />
<br />
		#endregion<br />
<br />
		#region Sendmessage clicks<br />
		public void PerformAPPLogin()<br />
		{<br />
			int hWndAPPLogin;<br />
<br />
			hWndAPPLogin = (int) data;<br />
<br />
			if ( hWndAPPLogin != 0 )<br />
			{<br />
				int hWndAPPLoginUserName;<br />
				int hWndAPPLoginPassWord;<br />
				int hWndAPPLoginOKButton;<br />
<br />
				hWndAPPLoginUserName = FindWindowEx(hWndAPPLogin,0,"Edit",null); // Find the UserName Edit Field in the APP Login Window<br />
				SendMessage(hWndAPPLoginUserName,WM_SETTEXT,0,"<UserName>"); // Enter the username of <UserName><br />
				hWndAPPLoginPassWord = FindWindowEx(hWndAPPLogin,hWndAPPLoginUserName,"Edit",null); // Find the PassWord Edit Field in the APP Login Window<br />
				SendMessage(hWndAPPLoginPassWord,WM_SETTEXT,0,"<Password>"); // Enter the password of <Password><br />
				hWndAPPLoginOKButton = FindWindowEx(hWndAPPLogin,0,"Button", null); // Find the OK button to perform login<br />
				SendMessage(hWndAPPLoginOKButton,BM_CLICK,0,null); // Press the OK button to perform login<br />
			}<br />
		}<br />
		<br />
		#endregion<br />
<br />
		#region Get APP Login Window<br />
		private void getAPPLogin()<br />
		{<br />
			bool APPRunning = false;<br />
<br />
			// Get all processes<br />
			Process[] processes = Process.GetProcesses();<br />
			for (int i=0;i <= processes.Length -1;i++)<br />
			{<br />
				if (processes[i].ProcessName.ToLower().IndexOf("<Name of Process>") != -1)<br />
				{<br />
					APPRunning = true;<br />
				}<br />
			}<br />
<br />
			if ( APPRunning )<br />
			{<br />
				// Get all APP Login windows<br />
<br />
				EnumWindowsCallback EnumWCB = new EnumWindowsCallback(displaySAPLogin);<br />
				EnumWindows(EnumWCB ,0);<br />
<br />
			}<br />
		}<br />
		<br />
		#endregion<br />
<br />
	}<br />
}<br />