Number input can emit empty value changes

[perry-blueberry]

Objective

Currently there's no event that emits a number input has changed to the empty value. You can do On<ValueChange<f32>> but you cannot do On<ValueChange<Option<f32>>>. This adds that possibility with the emit_value_change_on_empty prop added. This is set to false by default so the previous behavior will be used by default.

Solution

Adds emit_value_change_on_empty to FeathersNumberInputProps to change the event to emit On<ValueChange<Option<T>>>. Add Empty to NumberInputValue to be able to set the value back.

I'm not 100% sure how template_value works but I hope I did that part correctly.

Testing

I've updated the feathers_gallery example to have the scalar value be able to be empty.

Showcase

Click to view showcase

[kfc35]

I think I would move the logic of

if !allow_empty && text_value.is_empty() {
        return;
    }

from emit_value_change into this function block

Otherwise, it appears that this case isn’t explicitly handled in this fn as is. The else block doesn’t appear to handle that case correctly (since it’s assuming the logic happened outside the function), so it can cause a moment of confusion.

[viridia]

I don't think this is the right answer. A better approach might be to add a dedicated "error" event.

This gets into the whole topic of field validation.