ValidateNumber

/// <summary>
        /// Extension method to validate that input text is a number.
        /// </summary>
        /// <param name="e">Key Press Event Initialization.</param>
        /// <param name="IsCalculation">if true then decimal point (.) is allowed, if false then decimal point (.) is not allowed</param>
        public static void ValidateNumber(this TextBox txt, KeyPressEventArgs e, bool IsCalculation)
        {
            if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar))
                if (e.KeyChar == '.' && IsCalculation)
                    if (txt.Text.IndexOf('.') > -1)
                        e.Handled = true;
                    else e.Handled = false;
                else e.Handled = true;
        }
Example: 
private void txtRollNo_KeyPress(object sender, KeyPressEventArgs e)
        {
            (sender as TextBox).ValidateNumber(e, false);
        }

Description

Validates that input text is a number

Details

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