Android数据库（sqlite）之Room

说在前面：

1、使用Room需要添加的依赖：

dependencies {
  def room_version = "2.2.3"

  implementation "androidx.room:room-runtime:$room_version"
  annotationProcessor "androidx.room:room-compiler:$room_version" // For Kotlin use kapt instead of annotationProcessor

  // optional - Kotlin Extensions and Coroutines support for Room
  implementation "androidx.room:room-ktx:$room_version"

  // optional - RxJava support for Room
  implementation "androidx.room:room-rxjava2:$room_version"

  // optional - Guava support for Room, including Optional and ListenableFuture
  implementation "androidx.room:room-guava:$room_version"

  // Test helpers
  testImplementation "androidx.room:room-testing:$room_version"
}

2、数据库可视化工具安装及使用说明

http://www.sqlitebrowser.org/

3、涉及到的知识：

工程案例：

一、APP描述：对Word实体进行增删改

二、编写思路：

1、画界面：

1）上边是一个ScrollView（数据多的时候可滑动),ScrollView内有一个TextView

2）下边是四个按键，分别代表，插入、删除、删除所有、修改。

2、创建实体（Entity）：

package com.me.roombasic;

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

@Entity
public class Word {
    @PrimaryKey(autoGenerate = true)
    private int id;
    @ColumnInfo(name = "姓名")
    private String name;
    @ColumnInfo(name = "外号")
    private  String other;

    public Word(String name, String other) {
        this.name = name;
        this.other = other;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getOther() {
        return other;
    }

    public void setOther(String other) {
        this.other = other;
    }
}

3、创建dao

package com.me.roombasic;

import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;
import androidx.room.Update;

import java.util.List;

@Dao
public interface WordDao {
    @Insert
    void  insertWord(Word ...words );

    @Update
    void updateWord(Word... words);

    @Delete
    void deleteWord(Word... words);

    @Query("DELETE FROM WORD")
    void deleteAllWords();

    @Query("SELECT * FROM WORD ORDER BY ID DESC")
    List<Word>  getAllWords();

}

4、创建database

package com.me.roombasic;

import androidx.room.Database;
import androidx.room.RoomDatabase;
@Database(entities = {Word.class},version = 1,exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {
    public abstract WordDao getWordDao();

}

5、暂时在mainActive.java中为TextView、Button绑定数据和监听：

package com.me.roombasic;

import androidx.appcompat.app.AppCompatActivity;
import androidx.room.Room;

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

import java.util.List;

public class MainActivity extends AppCompatActivity {
    WordDao wordDao;
    WordDatabase wordDatabase;
    Button buttonInsert,buttonUpdate,buttonDelete,buttonQuery;
    TextView textView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = findViewById(R.id.textView);
        buttonInsert = findViewById(R.id.buttoninster);
        buttonUpdate = findViewById(R.id.buttonupdate);
        buttonDelete = findViewById(R.id.buttondelete);
        buttonQuery = findViewById(R.id.buttonquery);
        wordDatabase = Room.databaseBuilder(this,WordDatabase.class,"word_database")
                .allowMainThreadQueries()
                .build();
        wordDao = wordDatabase.getWordDao();
        updateView();
        buttonInsert.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word1 = new Word("谷子腾","恶霸");
                Word word2 = new Word("张凯鑫","胖鑫");
                Word word3 = new Word("王正帅","笑天");
                wordDao.insertWord(word1,word2,word3);
                updateView();
            }
        });
        buttonUpdate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word2 = new Word("张凯鑫","bujv");
                word2.setId(2);
                wordDao.updateWord(word2);
                updateView();
            }
        });
        buttonDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word2 = new Word("张凯鑫","胖鑫");
                word2.setId(3);
                wordDao.deleteWord(word2);
                updateView();
            }
        });buttonQuery.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                wordDao.deleteAllWords();
                updateView();
            }
        });
    }


    void updateView(){
        List<Word> list = wordDao.getAllWords();
        String text = "";
        for(int i=0;i<list.size();i++){
            text += list.get(i).getId() + ":" + list.get(i).getName() + "=" + list.get(i).getOther() + "\n";
        }
        textView.setText(text);
    }
}