ViewModelProvider.Factory 总是返回一个视图模型

Question

I have a TabLayout , contains three Fragment (Created by same instance) by SectionsPagerAdapter . Inside the fragment, I try with ViewModelProvider.Factory to create independent viewmodel, however, I found all fragments always update content together with same data.

I have debugged and found it always return the same viewmodel even with difference BillType , and something's weird that when enterence into activity, the Factory.create is only invoked once.

// Log
D/BillType: OUTCOME
D/Factory crate BillType: OUTCOME
D/ViewModel Init BillType: OUTCOME
D/viewModel Bill:BillType: OUTCOME
D/BillType: INCOME
D/viewModel Bill:BillType: OUTCOME
D/BillType: TRANSFER
D/viewModel Bill:BillType: OUTCOME

I cannot figure out where is wrong, same code runs correctly before.

class BillViewModel(billType: BillType): ViewModel() {
    val bill: MutableLiveData<Bill> = MutableLiveData()

    init {
        Log.d("ViewModel Init BillType", billType.toString())
        bill.value = Bill.QBill().apply {
            type = billType
        }
    }

    class NewBillViewModelFactory(val billType: BillType): ViewModelProvider.Factory {
        override fun <T : ViewModel?> create(modelClass: Class<T>): T {
            Log.d("Factory crate BillType", billType.toString())
            return modelClass.getConstructor(BillType::class.java)
                .newInstance(billType)
        }
    }
}

enum class BillType(val type: Int) {
    OUTCOME(0),
    INCOME(1),
    TRANSFER(2);
}

class NewBillFragment: BaseFragment() {
    ...
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        billType = BillType.values()[arguments?.getInt(BILLTYPE, 0) ?: 0]
        Log.d("BillType", billType.toString())
        viewModel = ViewModelProvider(requireActivity(), NewBillViewModel.NewBillViewModelFactory(billType))[NewBillViewModel::class.java]
        Log.d("viewModel Bill:BillType", viewModel.bill.value?.type.toString())
        _binding = FragmentBillNewBinding.inflate(layoutInflater, container, false)
        with(binding) {
            data = viewModel
            lifecycleOwner = activity
        ... ui ...
        return binding.root
    }

    companion object {
        private const val BILLTYPE = "billtype"

        @JvmStatic
        fun newInstance(billType: Int): NewBillFragment {
            return NewBillFragment().apply {
                arguments = Bundle().apply {
                    putInt(BILLTYPE, billType)
                }
            }
        }
    }
}

class SectionsPagerAdapter(private val context: Context, fm: FragmentManager)
    : FragmentPagerAdapter(fm) {

    override fun getItem(position: Int): Fragment = BillFragment.newInstance(position)

    override fun getPageTitle(position: Int): CharSequence = context.resources.getString(TAB_TITLES[position])

    override fun getCount(): Int = 3
}

Answer 1

Because you are creating a Shared ViewModel with requireActivity() . So it will return ViewModel with reference to Activity not Fragment.

If you want to keep ViewModel Fragment scoped Then you should pass Fragment as ViewModelStoreOwner .

        viewModel = ViewModelProvider(this, NewBillViewModel.NewBillViewModelFactory(billType))[NewBillViewModel::class.java]