Validating a Textbox field for only numeric input.

Question

I have created a form-based program that needs some input validation. I need to make sure the user can only enter numeric values within the distance Textbox.

So far, I've checked that the Textbox has something in it, but if it has a value then it should proceed to validate that the entered value is numeric:

else if (txtEvDistance.Text.Length == 0)
        {
            MessageBox.Show("Please enter the distance");
        }
else if (cboAddEvent.Text //is numeric)
        {
            MessageBox.Show("Please enter a valid numeric distance");
        }

Answer 1

I agree with Int.TryParse but as an alternative you could use Regex.

 Regex nonNumericRegex = new Regex(@"\D");
 if (nonNumericRegex.IsMatch(txtEvDistance.Text))
 {
   //Contains non numeric characters.
   return false;
 }

Answer 2

Here is another simple solution

try
{
    int temp=Convert.ToInt32(txtEvDistance.Text);
}
catch(Exception h)
{
    MessageBox.Show("Please provide number only");
}

Answer 3

You can do it by javascript on client side or using some regex validator on the textbox.

Javascript

script type="text/javascript" language="javascript">
    function validateNumbersOnly(e) {
        var unicode = e.charCode ? e.charCode : e.keyCode;
        if ((unicode == 8) || (unicode == 9) || (unicode > 47 && unicode < 58)) {
            return true;
        }
        else {

            window.alert("This field accepts only Numbers");
            return false;
        }
    }
</script>

Textbox (with fixed ValidationExpression)

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator ID="RegularExpressionValidator6" runat="server" Display="None" ErrorMessage="Accepts only numbers." ControlToValidate="TextBox1" ValidationExpression="^[0-9]*$" Text="*"></asp:RegularExpressionValidator> 

Answer 4

If you want to prevent the user from enter non-numeric values at the time of enter the information in the TextBox, you can use the Event OnKeyPress like this:

private void txtAditionalBatch_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (!char.IsDigit(e.KeyChar)) e.Handled = true;         //Just Digits
            if (e.KeyChar == (char)8) e.Handled = false;            //Allow Backspace
            if (e.KeyChar == (char)13) btnSearch_Click(sender, e);  //Allow Enter            
        }

This solution doesn't work if the user paste the information in the TextBox using the mouse (right click / paste) in that case you should add an extra validation.

Answer 5

You may try the TryParse method which allows you to parse a string into an integer and return a boolean result indicating the success or failure of the operation.

int distance;
if (int.TryParse(txtEvDistance.Text, out distance))
{
    // it's a valid integer => you could use the distance variable here
}

Answer 6

I have this extension which is kind of multi-purpose:

    public static bool IsNumeric(this object value)
    {
        if (value == null || value is DateTime)
        {
            return false;
        }

        if (value is Int16 || value is Int32 || value is Int64 || value is Decimal || value is Single || value is Double || value is Boolean)
        {
            return true;
        }

        try
        {
            if (value is string)
                Double.Parse(value as string);
            else
                Double.Parse(value.ToString());
            return true;
        }
        catch { }
        return false;
    }

It works for other data types. Should work fine for what you want to do.