I used ViewModel with LiveData in LifecycleActivity and Fragments it works and observes data as expected. Coming to your problem, when you create new ViewModel from Service or any another Activity it creates new instance of all the LiveData and other dependencies required for ViewModel to query from Repository and ultimately DAO. If you are … Read more
You can use my helper method: val profile = MutableLiveData<ProfileData>() val user = MutableLiveData<CurrentUser>() val title = profile.combineWith(user) { profile, user -> “${profile.job} ${user.name}” } fun <T, K, R> LiveData<T>.combineWith( liveData: LiveData<K>, block: (T?, K?) -> R ): LiveData<R> { val result = MediatorLiveData<R>() result.addSource(this) { result.value = block(this.value, liveData.value) } result.addSource(liveData) { result.value = … Read more
I have introduced just one change in your code: noteViewModel = ViewModelProviders.of(this).get(NoteViewModel.class); instead of: noteViewModel = ViewModelProviders.of(getActivity()).get(NoteViewModel.class); in Fragment‘s onCreate(Bundle) methods. And now it works seamlessly. In your version you obtained a reference of NoteViewModel common to both Fragments (from Activity). ViewModel had Observer registered in previous Fragment, I think. Therefore LiveData kept reference to … Read more
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
There is simple solution in Transformations method distinctUntilChanged.expose new data only if data was changed. In this case we get data only when it changes in source: LiveData<YourType> getData(){ return Transformations.distinctUntilChanged(LiveData<YourType> source)); } But for Event cases is better to use this: https://stackoverflow.com/a/55212795/9381524
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
I had a similar problem using Dagger 2 that was caused by having different instances of the Dao, one for updating/inserting data, and a different instance providing the LiveData for observing. Once I configured Dagger to manage a singleton instance of the Dao, then I could insert data in the background (in my case in … Read more
Based on the documentation: setValue(): Sets the value. If there are active observers, the value will be dispatched to them. This method must be called from the main thread. postValue(): Posts a task to a main thread to set the given value. If you called this method multiple times before a main thread executed a … Read more
I`m using this EventWraper class from Google Samples inside MutableLiveData /** * Used as a wrapper for data that is exposed via a LiveData that represents an event. */ public class Event<T> { private T mContent; private boolean hasBeenHandled = false; public Event( T content) { if (content == null) { throw new IllegalArgumentException(“null values … Read more
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