RecyclerViewAdapter

package com.example.roomtwo;

import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.lifecycle.LiveData;
import androidx.recyclerview.widget.ListAdapter;
import androidx.recyclerview.widget.RecyclerView;

import com.example.roomtwo.dao.Word;

import java.util.List;

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.InnerHolder> {

    List<Word> allWordLive = null;

    public void setAllWordLive(List<Word> allWordLive) {
        this.allWordLive = allWordLive;
    }

    //创建viewHolder的时候呼叫的
    @NonNull
    @Override
    public RecyclerViewAdapter.InnerHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = View.inflate(parent.getContext(), R.layout.recyclerview_item, null);
        return new InnerHolder(view);
    }

    //viewHolder和recyclerview绑定时呼叫的
    @Override
    public void onBindViewHolder(@NonNull RecyclerViewAdapter.InnerHolder holder, int position) {
        Word word = allWordLive.get(position);
        holder.textView_word.setText(String.valueOf((position+1)+": "+word.getWord()));
        holder.textView_meaning.setText(String.valueOf(word.getChineseMeaning()));
    }

    @Override
    public int getItemCount() {
        return allWordLive.size();
    }

    public class InnerHolder extends RecyclerView.ViewHolder {
        TextView textView_word;
        TextView textView_meaning;
        public InnerHolder(@NonNull View itemView) {
            super(itemView);
            textView_word = itemView.findViewById(R.id.item_word);
            textView_meaning = itemView.findViewById(R.id.item_meaning);
        }
    }
}

RecyclerViewAdapter

MainActivity

package com.example.roomtwo;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;
import androidx.lifecycle.ViewModelProviders;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import androidx.room.Room;

import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import com.example.roomtwo.dao.Word;
import com.example.roomtwo.dao.WordDao;
import com.example.roomtwo.dao.WordDatabase;

import java.util.List;

public class MainActivity extends AppCompatActivity {

    WordViewModel wordViewModel;
    RecyclerViewAdapter adapter;

    RecyclerView myRecyclerView;
    Button insertBtn;
    Button updateBtn;
    Button clearBtn;
    Button deleteBtn;

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

        //viewModel的实例化
        wordViewModel = ViewModelProviders.of(this).get(WordViewModel.class);

        //******************************recyclerview************************************************
        myRecyclerView = findViewById(R.id.myrecyclerview);
        adapter = new RecyclerViewAdapter();
        myRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        myRecyclerView.setAdapter(adapter);

        //可被观察的数据
        wordViewModel.getAllWordLive().observe(this, new Observer<List<Word>>() {
            @Override
            public void onChanged(List<Word> words) {
                adapter.setAllWordLive(words);
                adapter.notifyDataSetChanged(); //告诉数据改变，刷新视图
            }
        });

        //初始化各组件
        initBtnAndView();

        //插入
        insertBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Word word = new Word("hello", "你好");
                Word word1 = new Word("world", "世界");
                wordViewModel.insertWords(word,word1);
            }
        });

        //清空数据库表
        clearBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                wordViewModel.deleteAllWords();
            }
        });

        //删除某一个字段
        deleteBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Word word = new Word("", "");
                word.setId(270);
                wordViewModel.deleteWords(word);
            }
        });

        updateBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Word word = new Word("", "");
                word.setId(269);
                wordViewModel.updateWords(word);
            }
        });
    }

    void initBtnAndView(){
        insertBtn = findViewById(R.id.insertBtn);
        updateBtn = findViewById(R.id.updateBtn);
        clearBtn = findViewById(R.id.clearBtn);
        deleteBtn = findViewById(R.id.deleteBtn);
    }



}

MainActivity