我具有以下设置：

• 持有 MainFragment
的单个 Mainactivity
• Mainactivity 具有用于存储整数列表的ViewModel
• Mainactivity 在此ViewModel中写入整数值
• 我想在 MainFragment
中打印这些值
• 我能够访问ViewModel实例，但无法从该实例获取List值

Mainactivity ：

public class Mainactivity extends AppCompatactivity {

private MainViewModel mViewModel;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_activity);
    mViewModel = ViewModelProviders.of(this).get(MainViewModel.class);

    // Adding integer values in ViewModel
    mViewModel.selectInteger(1);
    mViewModel.selectInteger(10);
    mViewModel.selectInteger(111);

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
            .replace(R.id.container,MainFragment.newInstance())
            .commitNow();
    }
}

}

MainFragment ：

public class MainFragment extends Fragment {

private MainViewModel mViewModel;

private TextView tv;

public static MainFragment newInstance() {
    return new MainFragment();
}

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater,@Nullable ViewGroup container,@Nullable Bundle savedInstanceState) {

    View rootView =  inflater.inflate(R.layout.main_fragment,container,false);
    tv = rootView.findViewById(R.id.myTextView);
    return rootView;
}

@Override
public void onactivityCreated(@Nullable Bundle savedInstanceState) {
    super.onactivityCreated(savedInstanceState);
    mViewModel = ViewModelProviders.of(getactivity()).get(MainViewModel.class);

    // I am getting error in below line,Not able to pass List of integer to formatList function
    mViewModel.getListOfInt().observe(getactivity(),{value -> {formatList(value)}});
}

private String formatList(List<Integer> list) {
    String returnValue = "";
    for(Integer a : list) {
        returnValue = returnValue + a;
    }
    return returnValue;
}

}

MainViewModel ：

public class MainViewModel extends ViewModel {
// TODO: Implement the ViewModel
private final MutableLiveData<List<Integer>> listOfInt = new MutableLiveData<List<Integer>>();


public MutableLiveData<List<Integer>> getListOfInt() {
       return listOfInt;
   }

   public void selectInteger(Integer a) {
       List<Integer> current = listOfInt.getvalue();
       current.add(a);
       listOfInt.setvalue(current);
   }
}

将整数列表传递给formatList()方法时出现错误。