Is it possible to enforce non-nullability of LiveData values?

Question

Is there any way to enforce non-nullability of LiveData values? Default Observer implementation seems to have @Nullable annotation which forces an IDE to suggest that the value might be null and should be checked manually:

public interface Observer<T> {
    /**
     * Called when the data is changed.
     * @param t  The new data
     */
    void onChanged(@Nullable T t);
}

Answer 1

If you use Kotlin, you can create much nicer non-null observe function with extension. There is an article about it. https://medium.com/@henrytao/nonnull-livedata-with-kotlin-extension-26963ffd0333

Answer 2

A new option is available if you use Kotlin. You can replace LiveData with StateFlow. It is more suitable for Kotlin code and provides built-in null safety.

Instead of using:

class MyViewModel {
    val data: LiveData<String> = MutableLiveData(null) // the compiler will allow null here!
}

class MyFragment: Fragment() {
    model.data.observe(viewLifecycleOwner) {
        // ...
    }
}

You can use:

class MyViewModel {
    val data: StateFlow<String> = MutableStateFlow(null) // compilation error!
}

class MyFragment: Fragment() {
    lifecycleScope.launch {
        model.data.collect {
          // ...
        }
    }
}

StateFlow is part of coroutines and to use the lifecycleScope you need to add the lifecycle-extensions dependency:

implementation "androidx.lifecycle:lifecycle-extensions:$lifecycle_version"

Note that this API has been experimental before coroutines 1.4.0.

Here's some additional reading about replacing LiveData with StateFlow.

As Igor Bubelov pointed out, another advantage of this approach is that it's not Android specific so it can be used in shared code in multiplatform projects.