android-livedata

How and where to use Transformations.switchMap?

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In the map() function LiveData userLiveData = …; LiveData userName = Transformations.map(userLiveData, user -> { return user.firstName + ” ” + user.lastName; // Returns String }); everytime the value of userLiveData changes, userName will be updated too. Notice that we are returning a String. In the switchMap() function: MutableLiveData userIdLiveData = …; LiveData userLiveData = … Read more

What is the difference between map() and switchMap() methods?

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As per the documentation Transformations.map() Applies a function on the value stored in the LiveData object, and propagates the result downstream. Transformations.switchMap() Similar to map, applies a function to the value stored in the LiveData object and unwraps and dispatches the result downstream. The function passed to switchMap() must return a LiveData object. In other … Read more

Why there’s a separate MutableLiveData subclass of LiveData?

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In LiveData – Android Developer Documentation, you can see that for LiveData, setValue() & postValue() methods are not public. Whereas, in MutableLiveData – Android Developer Documentation, you can see that, MutableLiveData extends LiveData internally and also the two magic methods of LiveData is publicly available in this and they are setValue() & postValue(). setValue(): set … Read more

LiveData remove Observer after first callback

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There is a more convenient solution for Kotlin with extensions: fun <T> LiveData<T>.observeOnce(lifecycleOwner: LifecycleOwner, observer: Observer<T>) { observe(lifecycleOwner, object : Observer<T> { override fun onChanged(t: T?) { observer.onChanged(t) removeObserver(this) } }) } This extension permit us to do that: liveData.observeOnce(this, Observer<Password> { if (it != null) { // do something } }) So to answer … Read more

Notify Observer when item is added to List of LiveData

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Internally, LiveData keeps track of each change as a version number (simple counter stored as an int). Calling setValue() increments this version and updates any observers with the new data (only if the observer’s version number is less than the LiveData’s version). It appears the only way to start this process is by calling setValue() … Read more