NumericUpDown should accept null as Value

Is your feature request related to a problem? Please describe. I have a form where “0” is a total valid value, but I want to make sure the user inserted this and does not use the “default” value provided by the system. In WPF I just left the field empty (‘null’) and checked if the field is not null on save

Describe the solution you’d like make Value nullable

Describe alternatives you’ve considered Create my own control

Additional context Fields should be empty

If you are OK with this change, I can provide a PR for this.

[robloo]

I just checked TextBox too. The Text property is still nullable even after the switch to nullable ref types. I’m very surprised it was stated this isn’t common. In fact every other input control i’m aware of supports this functionality.

[robloo]

@danwalmsley There are many scenario where apps need to know if a user has/has-not made a selection. Zero in the case of a NumericUpDown is a valid number and is not enough to indicate no user-selection. This type of functionality is common in LOB apps where form field values are being entered. In fact every single control I am aware of has some way of keeping 'null/empty values for no user-selection.

When the NumberBox spec was widely discussed with Microsoft this was also a valid scenario. However double.NaN could be used to add this functionality. With the switch to decimal in Avalonia that was overlooked and it needs to be added back somehow.

There are two standardized ways of doing this:

1. Add a nullable SelectedValue property along with Value. This is the strategy used in DatePicker where the underlying type doesnt support empty/null.
2. In something like TextBox, null has historically been supported for this but string itself has an Empty state so can be used for this info as well. So these controls don’t need a special case and additional property because the underlying type supports it.