Question

I have a WPF textbox that is databound. I need to restrict the user input on the textbox so that it only accepts numbers and a single period (For displaying decimals).

I know I can handle this in “Winforms” way and validate each input on KeyPress event, but I was wondering if there was a cleaner and maybe even proper way to do this in WPF (especially since I am databinding the textbox).

Answer 1

Use ValidationRules provided by WPF.

The xaml would be:

<TextBox>
    <TextBox.Text>
        <Binding Path="Name">
            <Binding.ValidationRules>
                <ExceptionValidationRule />
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

The code for the textbox property would be (used regex for the validation):

public string Name
{
    get { return _name; }
    set
    {
        _name = value;
        if (!Regex.IsMatch(value, @"^((?:[1-9]\d*)|(?:(?=[\d.]+)(?:[1-9]\d*|0)\.\d+))$"))
        {
            throw new ApplicationException("Please enter only numbers/decimals.");
        }
    }
}

Source: Validation in WPF

---

The regex given above: ^((?:[1-9]\d*)|(?:(?=[\d.]+)(?:[1-9]\d*|0)\.\d+))$ can be tested at this Rubular link

The regex would match these:

1.2
22522
0.33
3.90000

but not these: (you could tweak the regex to allow some of them)

.999
23.35.1343
03423.23423