Question

I have a textbox that I’m trying to limit in two ways:

1 – I only want to allow numeric values, no decimals

2 – I only want to accept numbers that are <= 35

I have the following events to handle this:

private void TextBoxWorkflowCountPreviewTextInput(object sender, TextCompositionEventArgs e)
{
    if (!IsNumeric(e.Text, NumberStyles.Integer)) e.Handled = true;
}

public bool IsNumeric(string val, NumberStyles numberStyle)
{
    double result;
    return double.TryParse(val, numberStyle, CultureInfo.CurrentCulture, out result);
}

private void TextBoxWorkflowCountTextChanged(object sender, TextChangedEventArgs e)
{
    if (!string.IsNullOrEmpty(textBoxWorkflowCount.Text) && Convert.ToInt32(textBoxWorkflowCount.Text) <= 35) e.Handled = true;
    else
    {
        MessageBox.Show("Must not be higher then 35");
        textBoxWorkflowCount.Text = "35";
    }
}

This on the surface works perfectly fine – except when the user either pastes data into the textbox (appears unavoidable) or even more curiously – if the user enters a number and then hits backspace (making the textbox blank again) the messagebox letting the user know that their value is >35 appears (even though that is definitely not the case). The first issue I can live with if I have to – but the second is game breaking and after 30 minutes of trying to solve it I’ve got nowhere. Help!

Answer 1

Your code is failing the first condition because

string.IsNullOrEmpty(textBoxWorkflowCount.Text) 

evaluates to true, so it’s falling through to the ‘else’, and displaying the message.

if (string.IsNullOrEmpty(textBoxWorkflowCount.Text) || Convert.ToInt32(textBoxWorkflowCount.Text) <= 35) e.Handled = true; 

should do the trick