java - ViewModelProviders 弃用的正确替代方案是什么？

Question

由于所说的贬值，我不再使用 ViewModelProviders.of(this)。我研究了其他问题并使用了答复中的代码。所有代码都没有错误，但当我尝试运行该应用程序时，出现异常。

此处发生错误。

Process: com.example.checkingin, PID: 555
    java.lang.RuntimeException: Cannot create an instance of class com.example.checkingin.MainViewModel
        at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:275)
        at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:106)
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:185)
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
        at com.example.checkingin.CheckInRecentList.onActivityCreated(CheckInRecentList.java:123)

checkin 最近列表

package com.example.checkingin;
import android.content.Context;
import android.net.Uri;
import android.os.Bundle;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
import java.util.List;

/**
 * A simple {@link Fragment} subclass.
 * Activities that contain this fragment must implement the
 * {@link CheckInRecentList.OnFragmentInteractionListener} interface
 * to handle interaction events.
 * Use the {@link CheckInRecentList#newInstance} factory method to
 * create an instance of this fragment.
 */
public class CheckInRecentList extends Fragment {
    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";
    private RecyclerView recyclerView;
    private RecyclerView.Adapter checkInListAdapter;
    //private RecyclerView.LayoutManager layoutManager;
    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;
    private MainViewModel mViewModel;
    private CheckInListAdapter adapter;
    private TextView checkInLastDateTime;
    private TextView checkInTitle;
    private TextView checkInDestinationName;
    private TextView checkInComments;

    private OnFragmentInteractionListener mListener;

    public CheckInRecentList() {
        // Required empty public constructor
    }

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment CheckInRecentList.
     */
    // TODO: Rename and change types and number of parameters
    public static CheckInRecentList newInstance(String param1, String param2) {
        CheckInRecentList fragment = new CheckInRecentList();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
    //      These were originally set up from the recycler view add to the fragment
    //          recyclerView = findViewById(R.id.check_in_recent_recycler_view);

                // use this setting to improve performance if you know that changes
                // in content do not change the layout size of the RecyclerView
                //recyclerView.setHasFixedSize(true);
/*
                // use a linear layout manager
                layoutManager = new LinearLayoutManager(this);
                recyclerView.setLayoutManager(layoutManager);
*/
                // specify an adapter (see also next example)
                //checkInListAdapter = new CheckInListAdapter();
     //           recyclerView.setAdapter(checkInListAdapter);
            }

   @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_check_in_recent_list, container, false);
    }

    // TODO: Rename method, update argument and hook method into UI event
    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }
    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        mViewModel = new ViewModelProvider(this).get(MainViewModel.class);**

        checkInLastDateTime = getView().findViewById(R.id.checkInLastDateTime);
        checkInTitle = getView().findViewById(R.id.checkInTitle);
        checkInDestinationName = getView().findViewById(R.id.checkInDestinationName);
        checkInComments = getView().findViewById(R.id.checkInComments);

        listenerSetup();
        observerSetup();
        recyclerSetup();
    }
    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    /**
     * This interface must be implemented by activities that contain this
     * fragment to allow an interaction in this fragment to be communicated
     * to the activity and potentially other fragments contained in that
     * activity.
     * <p>
     * See the Android Training lesson <a href=
     * "http://developer.android.com/training/basics/fragments/communicating.html"
     * >Communicating with Other Fragments</a> for more information.
     */
    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        void onFragmentInteraction(Uri uri);
    }
    private void clearFields() {
        checkInLastDateTime.setText("");
        checkInDestinationName.setText("");
        checkInTitle.setText("");
        checkInComments.setText("");
    }

    private void listenerSetup() {

        Button editCheckInButton = getView().findViewById(R.id.checkInEditButton);
        Button resendCheckInButton = getView().findViewById(R.id.checkInResendButton);

        editCheckInButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
        //put in edit check in logic
            }
        });
        resendCheckInButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
        //put in resend logic
            }
        });

        }

    private void observerSetup() {

        mViewModel.getAllCheckIn().observe(getViewLifecycleOwner(), new Observer<List<CheckInTable>> ()
{
            @Override
            public void onChanged(@Nullable final List<CheckInTable> checkIn) {
                adapter.setCheckInList(checkIn);
            }
        });

        mViewModel.getSearchCheckInResults().observe(getViewLifecycleOwner(), new Observer<List<CheckInTable>>() {
            @Override
            public void onChanged(@Nullable final List<CheckInTable> checkIn) {

                        if (checkIn.size() > 0) {

                            checkInLastDateTime.setText(checkIn.get(0).getCheckInLastDateTime());
                            checkInDestinationName.setText(checkIn.get(0).getCheckInDestinationName());
                            checkInTitle.setText(checkIn.get(0).getCheckInTitle());
                            checkInComments.setText(checkIn.get(0).getCheckInComments());
                        } else {
                            checkInLastDateTime.setText("None Found");
                        }
                    }
                });
    }
    private void recyclerSetup() {

        RecyclerView recyclerView;

        adapter = new CheckInListAdapter(R.layout.recycler_view_item);
        recyclerView = getView().findViewById(R.id.check_in_recent_recycler_view);
        recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
        recyclerView.setAdapter(adapter);
    }
}

MainViewModel

package com.example.checkingin;
import android.app.Application;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import java.util.List;

public class MainViewModel extends AndroidViewModel {

    private CheckInRecipientsTableRepository checkInRecipientsTableRepository;
    private LiveData<List<CheckInRecipientsTable>> allRecipients;
    private MutableLiveData<List<CheckInRecipientsTable>> searchRecipientResults;

    private ContactGroupsTableRepository contactGroupsTableRepository;
    private LiveData<List<ContactGroupsTable>> allContactGroups;
    private MutableLiveData<List<ContactGroupsTable>> searchContactGroupsResults;

    private CheckInTableRepository checkInTableRepository;
    private LiveData<List<CheckInTable>> allCheckIn;
    private MutableLiveData<List<CheckInTable>> searchCheckInResults;

    public MainViewModel (Application application) {
        super(application);

        checkInRecipientsTableRepository = new CheckInRecipientsTableRepository(application);
        allRecipients = checkInRecipientsTableRepository.getAllCheckInRecipients();
        searchRecipientResults = checkInRecipientsTableRepository.getSearchRecipientResults();

        checkInTableRepository = new CheckInTableRepository(application);
        allCheckIn = checkInTableRepository.getAllCheckIn();
        searchCheckInResults = checkInTableRepository.getSearchCheckInResults();

        contactGroupsTableRepository = new ContactGroupsTableRepository(application);
        allContactGroups = contactGroupsTableRepository.getAllContactGroups();
        searchContactGroupsResults = contactGroupsTableRepository.getSearchContactGroupsResults();
    }


    MutableLiveData<List<CheckInRecipientsTable>> getSearchRecipientResults() {
        return getSearchRecipientResults();
    }
    LiveData<List<CheckInRecipientsTable>> getAllCheckInRecipients() {
        return getAllCheckInRecipients();
    }

    public void insertCheckInRecipientsTable(CheckInRecipientsTable checkInRecipientsTable) {
        checkInRecipientsTableRepository.insertCheckInRecipientsTable(checkInRecipientsTable);
    }
    public void deleteCheckInRecipient(int checkInPrimaryKey) {
        checkInRecipientsTableRepository.deleteCheckInRecipient(checkInPrimaryKey);
    }
    public void findCheckInRecipient(int checkInPrimaryKey) {
        checkInRecipientsTableRepository.findCheckInRecipient(checkInPrimaryKey);
    }


    MutableLiveData<List<ContactGroupsTable>> getSearchContactGroupsResults() {
        return getSearchContactGroupsResults();
    }
    LiveData<List<ContactGroupsTable>> getAllContactGroups() {
        return getAllContactGroups();
    }

    public void insertContactGroupsTable(ContactGroupsTable contactGroupsTable) {
        contactGroupsTableRepository.insertContactGroups(contactGroupsTable);
    }
    public void deleteContactGroups(int contactGroupsTablePrimaryKey) {
        contactGroupsTableRepository.deleteContactGroups(contactGroupsTablePrimaryKey);
    }
    public void findContactGroups(int contactGroupsTablePrimaryKey) {
        contactGroupsTableRepository.findContactGroups(contactGroupsTablePrimaryKey);
    }

    MutableLiveData<List<CheckInTable>> getSearchCheckInResults() {
        return getSearchCheckInResults();
    }
    LiveData<List<CheckInTable>> getAllCheckIn() {
        return getAllCheckIn();
    }

    public void insertCheckInTable(CheckInTable checkInTable) {
        checkInTableRepository.insertCheckIn(checkInTable);
    }
    public void deleteCheckIn(int checkInTablePrimaryKey) {
        checkInTableRepository.deleteCheckIn(checkInTablePrimaryKey);
    }
    public void findCheckIn(int checkInTablePrimaryKey) {
        checkInTableRepository.findCheckIn(checkInTablePrimaryKey);
    }
}

Answer 1

您将需要创建一个 ViewModelFactory，一个实现 ViewModelProvider.Factory 的类，因为您的 ViewModel 不使用默认的无参数构造函数。您可以修改this并将 UserDataSource 替换为 Application 。

在 Fragment 中创建 ViewModelFactory 对象后(理想情况下您应该执行此 onAttach 或 onCreate 操作)，替换

mViewModel = new ViewModelProvider(this).get(MainViewModel.class);

与

mViewModel = new ViewModelProvider(this, viewModelFactory).get(MainViewModel.class);