livedata-combineutil-java VS sunflower

3.) the MutableLiveDatas in the ViewModel initialized by SavedStateHandle.getLiveData should contain the fromDate and the toDate, and with the combination of these LiveDatas you can evaluate what to show on the screen

well the third-party libraries help but internally it's just MediatorLiveData which does ship with LiveData

If you're using Google's defaults, then you use a ViewModel created by Hilt and getting a reference to a SavedStateHandle, your state would be created of multiple MutableLiveDatas (each holding 1 property) created via savedStateHandle.getLiveData(), then you use MediatorLiveData (you can use a library like this or this) to combine the changes of the mutable properties into a single immutable state object observed by the "UI" (read: the view controller, aka the Fragment) using the viewLifecycleOwner property of Fragments.

MutableLiveData (java combiner/kotlin combiner) == BehaviorRelay (kotlin combiner) == MutableSharedFlow (kotlin combiner) conceptually, so it's not important to me which one it is, as long as you can throw combiners at it.

Yep, that's why I have this kotlin combiner/java combiner for LiveData, but map/switchMap also rely on MediatorLiveData.

people exposing 11 public LiveData fields for 11 private MutableLiveData fields instead of using MediatorLiveData as combiners to reduce the number of exposed LiveData fields

While it is possible to combine these properties into a single emission using MediatorLiveData, if the MutableLiveData is exposed as MutableLiveData, then the fields can be directly two-way databound to XML, which is kinda the original goal and purpose of databinding.

If you need help with combiners you can also check https://github.com/Zhuinden/livedata-combineutil-java/

If you can't join them, you can combine LiveDatas and then map them to a common representation so that the adapter can treat it as a single list. And use itemViewType to determine which view to show per each item.

Here is full code

https://github.com/android/sunflower?

If you want to open a project in Android Studio, you need its original source code. For instance, go here, then click Code > Download ZIP.

Technically the 2019 version of this repo https://github.com/android/sunflower/tree/5d5dd9e1f0bee1ef506d70aaacf21fe893a9fb83 was significantly less clear than newer versions.

Check out their example of the perfect app https://github.com/android/sunflower

Like looking at Google's android/sunflower app... I see it and it see how they are all divided viewmodel/fragment/workers but what should I be paying attention to when looking at sample apps to learn ?

Lastly, the problem with dig around is, my team is starting a project from scratch so there is nothing to reference. Android at least have some "best practice" example to follow (https://github.com/android/sunflower) Is there something like that for Spring?

After you are quite proficient with the framework, this time you should discover new things. The most trusted source is the samples from Google, for example, Sunflower