How to emit distinct values from MutableLiveData?

There is already in API : Transformations.distinctUntilChanged()

distinctUntilChanged

public static LiveData<X> distinctUntilChanged (LiveData<X> source)

Creates a new LiveData object does not emit a value until the source LiveData value has been changed. The value is considered changed if equals() yields false.

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If we talk about MutableLiveData, you can create a class and override setValue and then only call through super if new value != old value

class DistinctUntilChangedMutableLiveData<T> : MutableLiveData<T>() {
    override fun setValue(value: T?) {
        if (value != this.value) {
            super.setValue(value)
        }
    }
}

You can use the following magic trick to consume "items being the same":

fun <T> LiveData<T>.distinctUntilChanged(): LiveData<T> = MediatorLiveData<T>().also { mediator ->
    mediator.addSource(this, object : Observer<T> {
        private var isInitialized = false
        private var previousValue: T? = null

        override fun onChanged(newValue: T?) {
            val wasInitialized = isInitialized
            if (!isInitialized) {
                isInitialized = true
            }
            if(!wasInitialized || newValue != previousValue) {
                previousValue = newValue
                mediator.postValue(newValue)
            }
        }
    })
}

If you want to check referential equality, it's !==.

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But it has since been added to Transformations.distinctUntilChanged.