我想在 Android 和 KOTLIN 中使用 MVVM 实现，请帮助我

Question

公共类 navagation_activity 扩展 AppCompatActivity {

private AppBarConfiguration mAppBarConfiguration;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_navagation_activity);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    FloatingActionButton fab = findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });
    DrawerLayout drawer = findViewById(R.id.drawer_layout);
    NavigationView navigationView = findViewById(R.id.nav_view);
    // Passing each menu ID as a set of Ids because each
    // menu should be considered as top level destinations.
    mAppBarConfiguration = new AppBarConfiguration.Builder(
            R.id.nav_home, R.id.nav_gallery, R.id.nav_slideshow,R.id.nav_vishal)
            .setDrawerLayout(drawer)
            .build();
    NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
    NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
    NavigationUI.setupWithNavController(navigationView, navController);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.navagation_activity, menu);
    return true;
}

@Override
public boolean onSupportNavigateUp() {
    NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
    return NavigationUI.navigateUp(navController, mAppBarConfiguration)
            || super.onSupportNavigateUp();
}

} ..................................................... ..................................................... ..

公共类 HomeFragment 扩展 Fragment 实现 LifecycleOwner {

private HomeViewModel homeViewModel;

public View onCreateView(@NonNull LayoutInflater inflater,
                         ViewGroup container, Bundle savedInstanceState) {
    homeViewModel = new ViewModelProvider(this).get(HomeViewModel.class);
    View root = inflater.inflate(R.layout.fragment_home, container, false);
    final TextView textView = root.findViewById(R.id.text_home);
    final RecyclerView recyclerView = root.findViewById(R.id.recyclerview);

    homeViewModel = new ViewModelProvider(getActivity()).get(HomeViewModel.class);
    Observer<List<CourseItem>> userListUpdateObserver = null;
    homeViewModel.getUserMutableLiveData().observe(getActivity(), userListUpdateObserver);
    homeViewModel.getText().observe(getViewLifecycleOwner(), new Observer<String>() {
        public void onChanged(@Nullable String s) {
            textView.setText(s);
        }
    });

    userListUpdateObserver = new Observer<List<CourseItem>>() {
        @Override
        public void onChanged(List<CourseItem> courseItems) {
            recyclerView.setHasFixedSize(true);
            recyclerView.setLayoutManager(new LinearLayoutManager(getActivity(), LinearLayoutManager.VERTICAL, false));
            RecyclerViewListAdapter recyclerViewListAdapter = new RecyclerViewListAdapter(getContext(), courseItems);
            recyclerView.setAdapter(recyclerViewListAdapter);
        }

    };
    homeViewModel.getText().observe(getViewLifecycleOwner(), new Observer<String>() {
        List<CourseItem> course;

        @Override
        public void onChanged(String s) {
            /*RecyclerViewListAdapter recyclerViewListAdapter = new RecyclerViewListAdapter(getContext(), course);
            recyclerView.setAdapter(recyclerViewListAdapter);*/
        }
    });
    return root;
}

} ..................................................... ....................................

公共类 HomeViewModel 扩展 ViewModel {

private MutableLiveData<String> mText;
private MutableLiveData<List<CourseItem>> mrecyclerview;
List<CourseItem> course;
public HomeViewModel() {
    mText = new MutableLiveData<>();
    mrecyclerview = new MutableLiveData<>();
    // call your Rest API in init method
    init();
  //  mText.setValue("This is home fragment");
}


private void init() {
    mrecyclerview.setValue(course);
    vishal();
}

private void vishal() {

    CourseItem courseItem = new CourseItem();
    courseItem.setAmount("100");
    courseItem.setCourseName("vishal is there");
    course = new ArrayList<>();
    course.add(courseItem);
    course.add(courseItem);
    course.add(courseItem);
    course.add(courseItem);
    course.add(courseItem);
    course.add(courseItem);
    course.add(courseItem);
    course.add(courseItem);
    course.add(courseItem);
    course.add(courseItem);
}

public LiveData<String> getText() {
    return mText;
}

public MutableLiveData<List<CourseItem>> getUserMutableLiveData() {
    return mrecyclerview;
}

}

Answer 1

让我来介绍一下 MVVM 的基本概念。你可以通过这个实现

1. ModelClass.kt - 您的数据模型
2. Service Class.kt - 在此处编写和管理您的 api 调用。您的模型将在此处填充。
3. 最后调用Mainactivity.kt的Service类方法就大功告成了。

注意：您的 xml 和 api 管理器将根据您的要求。