RecyclerView项目删除，但当我移动到不同的活动并返回时，该项目会恢复

Question

我在我的recyclerView中添加了一些新代码，当向左或向右滑动时会删除该项目，但当我移动到另一个活动，然后返回到我的recyclerView活动时，这些项目会重新出现。下面是我的MainActivity(名为TestGroceryList)的代码：

public class TestGroceryList extends AppCompatActivity {

    private WordViewModel mWordViewModel;
    public static final int NEW_WORD_ACTIVITY_REQUEST_CODE = 1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test_grocery_list);
        RecyclerView recyclerView = findViewById(R.id.recyclerview);
        final WordListAdapter adapter = new WordListAdapter(this);
        recyclerView.setAdapter(adapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        mWordViewModel = new ViewModelProvider(this).get(WordViewModel.class);
        mWordViewModel.getAllWords().observe(this, new Observer<List<Word>>() {
            @Override
            public void onChanged(@Nullable final List<Word> words) {
                // Update the cached copy of the words in the adapter.
                adapter.setWords(words);
            }
        });

        new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(0, ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT) {
            @Override
            public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {
                return false;
            }

            @Override
            public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {
                WordViewModel.delete(adapter.getWordAt(viewHolder.getAdapterPosition()));
                Toast.makeText(TestGroceryList.this, "Item Deleted!", Toast.LENGTH_SHORT).show();

            }
        }).attachToRecyclerView(recyclerView);

        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(TestGroceryList.this, NewWordActivity.class);
                startActivityForResult(intent, NEW_WORD_ACTIVITY_REQUEST_CODE);
            }
        });
    }

    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == NEW_WORD_ACTIVITY_REQUEST_CODE && resultCode == RESULT_OK) {
            Word word = new Word(data.getStringExtra(NewWordActivity.EXTRA_REPLY));
            mWordViewModel.insert(word);
        } else {
            Toast.makeText(
                    getApplicationContext(),
                    R.string.empty_not_saved,
                    Toast.LENGTH_LONG).show();
        }
    }

下面是我的Adapter的代码：

public class WordListAdapter extends RecyclerView.Adapter<WordListAdapter.WordViewHolder> {


    static class WordViewHolder extends RecyclerView.ViewHolder {
        private final TextView wordItemView;

        private WordViewHolder(View itemView) {
            super(itemView);
            wordItemView = itemView.findViewById(R.id.textView);
        }
    }

    private final LayoutInflater mInflater;
    private List<Word> mWords; // Cached copy of words

    WordListAdapter(Context context) { mInflater = LayoutInflater.from(context); }

    @Override
    public WordViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = mInflater.inflate(R.layout.recycler_item, parent, false);
        return new WordViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(WordViewHolder holder, int position) {
        if (mWords != null) {
            Word current = mWords.get(position);
            holder.wordItemView.setText(current.getWord());
        } else {
            // Covers the case of data not being ready yet.
            holder.wordItemView.setText("No thecookbookerapp.com.Word");
        }
    }

    void setWords(List<Word> words){
        mWords = words;
        notifyDataSetChanged();
    }

    public Word getWordAt(int position){
        return mWords.get(position);
    }


    // getItemCount() is called many times, and when it is first called,
    // mWords has not been updated (means initially, it's null, and we can't return null).
    @Override
    public int getItemCount() {
        if (mWords != null)
            return mWords.size();
        else return 0;
    }
}

这是我的WordViewModel：

package thecookbookerapp.com;

import android.app.Application;
import android.content.Intent;
import android.widget.Toast;

import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;

import java.util.List;

import static android.app.Activity.RESULT_OK;
import static 
thecookbookerapp.com.TestGroceryList.NEW_WORD_ACTIVITY_REQUEST_CODE;

public class WordViewModel extends AndroidViewModel {

private WordRepository mRepository;

private LiveData<List<Word>> mAllWords;

public WordViewModel (Application application) {
    super(application);
    mRepository = new WordRepository(application);
    mAllWords = mRepository.getAllWords();
}

public static void delete(Word wordAt) {

}

LiveData<List<Word>> getAllWords() { return mAllWords; }

public void insert(Word word) { mRepository.insert(word); }

}

这是我的WordRepository：

class WordRepository {

private WordDao mWordDao;
private LiveData<List<Word>> mAllWords;

// Note that in order to unit test the WordRepository, you have to remove the Application
// dependency. This adds complexity and much more code, and this sample is not about testing.
// See the BasicSample in the android-architecture-components repository at
// https://github.com/googlesamples
WordRepository(Application application) {
    WordRoomDatabase db = WordRoomDatabase.getDatabase(application);
    mWordDao = db.wordDao();
    mAllWords = mWordDao.getAlphabetizedWords();
}

// Room executes all queries on a separate thread.
// Observed LiveData will notify the observer when the data has changed.
LiveData<List<Word>> getAllWords() {
    return mAllWords;
}

// You must call this on a non-UI thread or your app will throw an exception. Room ensures
// that you're not doing any long running operations on the main thread, blocking the UI.
void insert(Word word) {
    WordRoomDatabase.databaseWriteExecutor.execute(() -> {
        mWordDao.insert(word);
    });
}
}

这是我的WordDao：

import androidx.room.Query;

import java.util.List;

@Dao
public interface WordDao {

// allowing the insert of the same word multiple times by passing a
// conflict resolution strategy
@Insert(onConflict = OnConflictStrategy.IGNORE)
void insert(Word word);

@Query("DELETE FROM word_table")
void deleteAll();

@Query("SELECT * from word_table ORDER BY word ASC")
LiveData<List<Word>> getAlphabetizedWords();

@Delete
void delete(Word word);

}

以下是我的问题的视频：Link

谁能帮帮我？谢谢

Answer 1

当你滑动一个项目时，你调用了WordViewModel.delete()；但实际上你需要在你的WordViewModel中实现这个方法，因为你把它留空了；

在Repository的add below方法中

public void delete(Word word) {
    WordRoomDatabase.databaseWriteExecutor.execute(() -> {
        mWordDao.delete(word);
    });
}

在ViewModel中修改delete方法为

public void delete(Word word) {
    mRepository.delete(word); 
}

并修改ItemTouchHelper onSwipe()以使用ViewModel非静态方法

@Override
public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {
    mWordViewModel.delete(adapter.getWordAt(viewHolder.getAdapterPosition()));
    Toast.makeText(TestGroceryList.this, "Item Deleted!", Toast.LENGTH_SHORT).show();

}