一个视图模型中的实时数据只能被一个地方观察到吗？

Question

I have a livedata in a viewmodel. and i observe the livedata in a fragment, another class,

when i change the livedata value, only the fragment can receive the notification of livedata change. not another class.

i wonder just only one place(ex: fragment, activity etc) can observe a livedata of viewmodel?

Answer 1

You are not getting it right. The way MVVM works is view interact with viewModel which is observer class and viewModel then interacts with repo class for db/remote operations. Reason why you are observing live data in fragment/activity is because as per design patter view can only access ViewModel that's why you are only able to observe it from fragment/activity class

Answer 2

The livedata can be observed by as many observers as you want.The observer if implements LifecycleOwner interface will get notified when in running state or you can observe it forever irrespective of lifecycle of the observer by using observeForever. But you will have to manually remove the observer to stop observing it.

LiveData considers an observer, which is represented by the Observer class, to be in an active state if its lifecycle is in the STARTED or RESUMED state. LiveData only notifies active observers about updates. Inactive observers registered to watch LiveData objects aren't notified about changes.