Proper null handling

I need to be able to observe a preference’s value (or lack of value or if it has been cleared). It’s very important to be able to keep the stream alive.

Observable<Optional<Boolean>> //note Optional is my own custom class

Would it be possible to pass in some function to handle a custom mapping when the preference is null?

[ZakTaccardi]

Use a sentinel value for the default. When the preference does not exist, the default value is emitted. Check the value against the sentinel value, if they’re equal the value does not exist.

This causes two problems

• Can’t use a sentinel value for a Boolean optional. We only have true and false…
• Duplicating extra work across users of this library. Ideally, the library itself should bear this burden

I know RxJava2’s lack of nullability without a proper optional is rather an annoying problem to solve. Worst case scenario, an optional implementation (maybe call it EmptyPreference<T>) would be better than nothing.

[ZakTaccardi]

You can use integers or enums or a custom object instead.

This could certainly work, but does android treat Boolean vs String preferences differently? What happens if you access a Boolean preference with sharedPrefs.getString(key) where the key already exists in a boolean preference. Does it just return true?

I need to be able to completely interop with the other non-reactive ways the app (co-workers) access the preference.

Ultimately I still suggest some type of converter a la Retrofit style to enable usage of custom Optional<T> types.