How to change the value of SNumericEntryBox via code?

I have an SNumericEntryBox with float values, which is “connected” to another input field. If one changes, the other has to change as well, therefore I need to change the value of the SNumericEntryBox from code.
How do I do that thought? There is no Value member, only a SLATE_ATTRIBUTE. There is no setter directly and I can’t change the text of the internal SEditableText widget (it throws an read access violation error if I try to, beacuse the TextLayout has not been set by the numerical entry box).
I don’t have access to the event methods OnValueCommited and such either.