Android studio：从数据库中删除项目时，如何更新回收站视图中的文本视图？

Question

So I've made a demo app to demonstrate my problem and have some pictures for my expected outcome. I'm using Room to create a database and a user is able to add an entry by pressing a button. There are only two fields: the id (primary key) and the row number. I set the row number by getting the number of entries through a query and adding one to that value. I then insert a new entry with the constructor requiring a row number.

I've added an option to where a user can swipe right to delete an entry, but I can't figure out how to update the row number and to change the row number displayed in the textview to be the proper row number. Here are some screenshots which might make what I'm asking easier to understand as I'm still pretty new.

I added 10 rows in the first picture, removed some rows in the second, and the third shows what I want the output to be, minus the paint writing:

Here is the code:

MainActivity.Java

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;
import androidx.recyclerview.widget.DividerItemDecoration;
import androidx.recyclerview.widget.ItemTouchHelper;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;

import java.util.List;

public class MainActivity extends AppCompatActivity {

    private TestViewModel testViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);



        Button addButton = findViewById(R.id.test_button);
        RecyclerView recyclerView = findViewById(R.id.recyclerView);
        recyclerView.addItemDecoration(new DividerItemDecoration(this, LinearLayout.VERTICAL));
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setHasFixedSize(true);

        final TestAdapter adapter = new TestAdapter();
        recyclerView.setAdapter(adapter);

        testViewModel = ViewModelProviders.of(this).get(TestViewModel.class);
        testViewModel.getAllTests().observe(this, new Observer<List<Test>>() {
            @Override
            public void onChanged(List<Test> tests) {
                adapter.submitList(tests);
            }
        });

        testViewModel.getNumberOfEntries().observe(this, new Observer<Integer>() {
            @Override
            public void onChanged(Integer integer) {

            }
        });

        new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(0,
                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) {
                testViewModel.delete(adapter.getTestAt(viewHolder.getAdapterPosition()));
            }
        }).attachToRecyclerView(recyclerView);

        addButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (testViewModel.getNumberOfEntries().getValue() != null) {
                    int rowNum = testViewModel.getNumberOfEntries().getValue() + 1;
                    testViewModel.insert(new Test(rowNum));
                }else{
                    int rowNum = 1;
                    testViewModel.insert(new Test(rowNum));
                }
            }
        });
    }


}

Test.Java

import androidx.room.Entity;
import androidx.room.PrimaryKey;

@Entity(tableName = "test_table")
public class Test {

    @PrimaryKey(autoGenerate = true)
    private int id;

    private int rowNumber;

    public Test(int rowNumber){
        this.rowNumber = rowNumber;
    }

    public int getId() {
        return id;
    }

    public int getRowNumber() {
        return rowNumber;
    }

    public void setId(int id) {
        this.id = id;
    }
}

TestAdapter.Java

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.DiffUtil;
import androidx.recyclerview.widget.ListAdapter;
import androidx.recyclerview.widget.RecyclerView;

import java.util.List;

public class TestAdapter extends ListAdapter <Test, TestAdapter.TestHolder> {

    protected TestAdapter() { super(DIFF_CALLBACK); }

    private static final DiffUtil.ItemCallback<Test> DIFF_CALLBACK = new DiffUtil.ItemCallback<Test>() {
        @Override
        public boolean areItemsTheSame(@NonNull Test oldItem, @NonNull Test newItem) {
            return newItem.getId() == oldItem.getId();
        }

        @Override
        public boolean areContentsTheSame(@NonNull Test oldItem, @NonNull Test newItem) {
            return newItem.getRowNumber() == oldItem.getRowNumber();
        }
    };

    @NonNull
    @Override
    public TestHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.test_item, parent, false);
        return new TestHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull TestAdapter.TestHolder holder, int position) {
        Test currentTest = getItem(position);

        holder.textViewRowNumber.setText(String.valueOf(currentTest.getRowNumber()));
    }

    public Test getTestAt(int position){ return  getItem(position);}

    class TestHolder extends RecyclerView.ViewHolder{
        private TextView textViewRowNumber;

        public TestHolder(View itemView){
            super(itemView);
            textViewRowNumber = itemView.findViewById(R.id.test_text_view);
        }
    }
}

TestDao.Java

import androidx.lifecycle.LiveData;
import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;

import java.util.List;

@Dao
public interface TestDao {

    @Insert
    void insert(Test test);

    @Delete
    void delete(Test test);

    @Query("SELECT * FROM test_table")
    LiveData<List<Test>> getAllEntries();

    @Query("SELECT Count(*) FROM test_table")
    LiveData<Integer>getNumberOfEntries();
}

TestDatabase.Java

import android.content.Context;

import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;

@Database(entities = Test.class, version = 1)

public abstract class TestDatabase extends RoomDatabase {

    private static TestDatabase instance;

    public abstract TestDao testDao();

    public static synchronized TestDatabase getInstance(Context context){
        if(instance == null){
            instance = Room.databaseBuilder(context.getApplicationContext(),
                    TestDatabase.class, "test_database")
                    .fallbackToDestructiveMigration()
                    .build();
        }
        return instance;
    }
}

TestRepository.Java

import android.app.Application;
import android.os.AsyncTask;

import androidx.lifecycle.LiveData;

import java.util.List;

public class TestRepository {
    private TestDao testDao;
    private LiveData<List<Test>> allTests;
    private LiveData<Integer> numberOfEntries;

    public TestRepository(Application application) {
        TestDatabase database = TestDatabase.getInstance(application);
        testDao = database.testDao();
        allTests = testDao.getAllEntries();
        numberOfEntries = testDao.getNumberOfEntries();
    }

    public void insert(Test test) {
        new InsertTestAsyncTask(testDao).execute(test);
    }

    public void delete(Test test) {
        new DeleteTestAsyncTask(testDao).execute(test);
    }

    public LiveData<Integer> getNumberOfEntries() {
        return numberOfEntries;
    }

    public LiveData<List<Test>> getAllTests() {
        return allTests;
    }

    private static class InsertTestAsyncTask extends AsyncTask<Test, Void, Void> {
        private TestDao testDao;

        private InsertTestAsyncTask(TestDao testDao) {
            this.testDao = testDao;
        }

        @Override
        protected Void doInBackground(Test... tests) {
            testDao.insert(tests[0]);
            return null;
        }
    }

    private static class DeleteTestAsyncTask extends AsyncTask<Test, Void, Void> {
        private TestDao testDao;

        private DeleteTestAsyncTask(TestDao testDao) {
            this.testDao = testDao;
        }

        @Override
        protected Void doInBackground(Test... tests) {
            testDao.delete(tests[0]);
            return null;
        }
    }

}

TestViewModel.Java

import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;

import java.util.List;

public class TestViewModel extends AndroidViewModel {
    private TestRepository repository;
    private LiveData<Integer> numberOfEntries;
    private LiveData<List<Test>> allTests;

    public TestViewModel(@NonNull Application application) {
        super(application);
        repository = new TestRepository(application);
        numberOfEntries = repository.getNumberOfEntries();
        allTests = repository.getAllTests();
    }

    public void insert(Test test) { repository.insert(test);}

    public void delete(Test test) { repository.delete(test);}

    public LiveData<Integer> getNumberOfEntries(){ return numberOfEntries; }

    public LiveData<List<Test>> getAllTests() { return allTests;}
}

Thanks!

Answer 1

Follow these steps, I hope it will help:

1. get your itemList from TestAdapter .

2. you can change any raw you want. (For example change data of item in raw 6)

3. send it back to the testAdapter .

4. call method notifyDataSetChanged(); .

5. if you only change one item at a time, it's better to call notifyItemChanged(position); abecause it has a better performance than notifyDataSetChanged();

You have more other tools like notifyItemInserted(position); notifyItemRemoved(position); notifyItemInserted(position); notifyItemRemoved(position); that might help you.

Answer 2

Try to modify your ItemTouchHelper implementation like below:

new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(0,
        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) {
        testViewModel.delete(adapter.getTestAt(viewHolder.getAdapterPosition()));

        //get current list from adapter
        List currentList = adapter.getCurrentList();

        //remove item from list 
        currentList.remove(viewHolder.getAdapterPosition());

        //submit the current list to refresh view
        adapter.submitList(currentList);
    }
}).attachToRecyclerView(recyclerView);