多个fragment内实现ViewModel的共享

在多个Fragment之间共享ViewModel，可以使用以下步骤：

1. 创建一个ViewModel类，该类包含需要共享的数据和方法。

public class SharedViewModel extends ViewModel {
    private MutableLiveData<String> selected = new MutableLiveData<String>();

    public void select(String item) {
        selected.setValue(item);
    }

    public LiveData<String> getSelected() {
        return selected;
    }
}

2. 在需要共享ViewModel的Fragment中，通过ViewModelProvider获取ViewModel实例。

public class Fragment1 extends Fragment {
    private SharedViewModel model;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        model = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);
    }

    // ...
}

3. 在其他需要访问ViewModel的Fragment中，也通过ViewModelProvider获取同一个ViewModel实例。

public class Fragment2 extends Fragment {
    private SharedViewModel model;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        model = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);
    }

    // ...
}

4. 在Fragment中使用ViewModel中的数据和方法。这样就可以在多个Fragment之间共享ViewModel了。

public class Fragment1 extends Fragment {
    private SharedViewModel model;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        model = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment1, container, false);
        Button button = view.findViewById(R.id.button);
        final EditText editText = view.findViewById(R.id.editText);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                model.select(editText.getText().toString());
            }
        });

        return view;
    }
}

public class Fragment2 extends Fragment {
    private SharedViewModel model;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        model = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment2, container, false);
        final TextView textView = view.findViewById(R.id.textView);

        model.getSelected().observe(getViewLifecycleOwner(), new Observer<String>() {
            @Override
            public void onChanged(String item) {
                textView.setText(item);
            }
        });

        return view;
    }
}