Validating a Textbox field for only numeric input.

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.

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
}