Android ViewModel 观察器不起作用？ 科特林

Question

Inside the fragment of a tabbed activity:

override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)
    serverSetVM = ViewModelProvider(activity!!).get(ServersViewModel::class.java)

    serverList = ArrayList(serverSetVM.get())
    rv = rv_serverList // findViewById 
    rv.layoutManager = LinearLayoutManager(context)
    rv.adapter = ServerListRevAdapter(context!! ,serverList) 

    serverSetVM.serverSetLiveData.observe(viewLifecycleOwner,  Observer {

        Log.v ("MainAct", "Inside OBSERVER")
        serverList = ArrayList(serverSetVM.get())
        rv.adapter!!.notifyDataSetChanged()
    })
}

Also;

val serverSetLiveData = MutableLiveData<HashSet<Server>>() // Inside ViewModel class

observe() function does not seem to work. When the value of ServerSetVM is modified inside the same fragment (by the functions defined in ViewModel class, ie add() ), recyclerView is not updated. According to Logcat output, Observer lambda is called only after onCreateView() .

I confirmed MutableLiveData gets updated but Observer{} lambda is not called. Do I need to correct my notion about ViewModels?

EDIT (SOLUTION): Use " = " operator to modify the MutableLiveData value so that observer can detect it. Even serverSetLiveData.value=serverSetLiveData.value does the job.

Answer 1

Observer only observe if you call setValue() or postValue() method of MutableLiveData

where you are calling the setValue() or postValue() function for serverSetLiveData . eg. serverSetLiveData.setValue(serverList) or serverSetLiveData.postValue(serverList). in the code.

Answer 2

仅当您调用.value =才会触发 Obervre