notifyDataSetChanged 不更新视图

Question

I am using viewModel in recycler view, but its not updating only if I enter and exist screen not in screen itself:

override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)
    viewModel = ViewModelProvider(requireActivity()).get(RideDataViewModel::class.java)

    rideList.adapter = MyRideListItemRecyclerViewAdapter(viewModel.rides.value!!, object : OnItemClickListener {
        override fun onItemClicked(ride: RideEntity) {
            viewModel.setRide(ride)
            findNavController().navigate(R.id.rideDataFragment)
        }
    })

    viewModel.rides.observe(viewLifecycleOwner, {

        if (it.isNotEmpty()) 
        {
            no_rides.visibility = View.GONE
           rideList.adapter!!.notifyDataSetChanged() //Function called but no visible data
        }
        else
        {
            no_rides.visibility = View.VISIBLE
        }
    })


    lifecycleScope.launch {
        viewModel.setRides(DataBaseHelper.getAllRidesFromDB())
    }
}

ViewModel:

class RideDataViewModel : ViewModel() {
    
        var rides= MutableLiveData<List<RideEntity>>(listOf())
        fun setRides(item: List<RideEntity>) {
            rides.postValue(item)
    }
}

Answer 1

You don't show your adapters code, but you need to set the adapters underlying data/list using the it reference before calling notifyDataSetChanged

if (it.isNotEmpty())  {
    no_rides.visibility = View.GONE
    rideList.adapter!!.data = it // something similar to set the list in your adapter to the new values
    rideList.adapter!!.notifyDataSetChanged() //Function called but no visible data
}

Answer 2

Where are you setting the list on your adapter? In your LiveData observer you're only calling notifyDataSetChanged() , which will only make the RecyclerView redraw the items, but you don't set the items first so it has nothing to redraw.

I don't know how your adapter looks, but something along the lines of the code below should make it update

if (it.isNotEmpty()) {
    no_rides.visibility = View.GONE
    rideList.adapter!!.list = it              // Update the list in the adapter
    rideList.adapter!!.notifyDataSetChanged() // Now this will have something to draw
}