Nullability and LiveData with Kotlin

You can create an extension for LifecycleOwner

fun <T> LifecycleOwner.observe(liveData: LiveData<T?>, lambda: (T) -> Unit) {
    liveData.observe(this, Observer { if (it != null) lambda(it) })
}

and then in your fragment/activity

observe(liveData) { ... }

You can do this

normalLiveData
  .nonNull()
  .observe(this, { result -> 
    // result is non null now
  })

There is an article about it. https://medium.com/@henrytao/nonnull-livedata-with-kotlin-extension-26963ffd0333

I little improve answer The Lucky Coder. This implementation cannot accept null values at all.

class NonNullMutableLiveData<T: Any>(initValue: T): MutableLiveData<T>() {

    init {
        value = initValue
    }

    override fun getValue(): T {
        return super.getValue()!!
    }

    override fun setValue(value: T) {
        super.setValue(value)
    }

    fun observe(owner: LifecycleOwner, body: (T) -> Unit) {
        observe(owner, Observer<T> { t -> body(t!!) })
    }

    override fun postValue(value: T) {
        super.postValue(value)
    }    
}

I don't know if this is the best solution but this is what I came up with and what I use:

class NonNullLiveData<T>(private val defaultValue: T) : MutableLiveData<T>() {

    override fun getValue(): T = super.getValue() ?: defaultValue

    fun observe(owner: LifecycleOwner, body: (T) -> Unit) {
        observe(owner, Observer<T> {
            body(it ?: defaultValue)
        })
    }
}

Creating the field:

val string = NonNullLiveData("")

And observing it:

viewModel.string.observe(this) {
    // Do someting with the data
}