C#

Application.ThreadException += ThreadExceptionHandler;
Application.Run(new Form1());
Application.ThreadException -= ThreadExceptionHandler;

Application.ThreadException += ThreadExceptionHandler;
try{
   Application.Run(new Form1());
}
finally{
   Application.ThreadException -= ThreadExceptionHandler;
}

public class RestrictedTextBox : TextBox
{
    private const int WM_PASTE = 0x0302;

    protected override void WndProc(ref Message m)
    {
        if (m.Msg == WM_PASTE)
        {
            if (!IsPasteValid())
            {
                m.Result = IntPtr.Zero;
                return;
            }
        }
        base.WndProc(ref m);
    }

    private bool IsPasteValid()
    {
        bool rtn = false;
        IDataObject obj = Clipboard.GetDataObject();
        string pasteString = (string)obj.GetData(typeof(string));
        // Do checks on pasteString here and set rtn to true if OK.
        return rtn;
    }
}

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            if ( Convert.ToInt16(e.KeyChar) >= 48 && Convert.ToInt16(e.KeyChar) <=57)
            {
                e.KeyChar = e.KeyChar;
            }
            else
            {
                e.KeyChar = Convert.ToChar(0);
            }
        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {
            char[] strSample = new char[((System.Windows.Forms.TextBox)(sender)).Text.ToString().Length];

            strSample = (((System.Windows.Forms.TextBox)(sender)).Text).ToCharArray();

            for (int i=0; i<strSample.Length;i++)
            {
                if (Convert.ToInt16(strSample[i]) >= 48 && Convert.ToInt16(strSample[i]) <= 57)
                {
                    continue;
                }
                else
                {
                    ((System.Windows.Forms.TextBox)(sender)).Text = "";
                    break;
                }
            }
            
        }

Guffa wrote:

There is no such class. Do you mean the System.Drawing.Font class?