前言

我们直接开门见山，展示一下效果：
数据库的插入和查询：

数据库的修改和查询：

可以看到id为23的数据发生了修改。

删除一条数据：

可以看到id为23的数据被删除了

删除全部数据：

可以看到，数据全都被删除了。
完整代码可运行项目：Android移动应用开发之使用room实现数据库的增删改查

注意：因为设置表的id是主键且自增，因此插入数据id就会持续增加，因为修改和删除都是在MainActivity中手动设置的，是个比较简单的demo，如果需要看到修改和条件删除的效果

修改此处的setId中的参数即可。

核心代码

首先需要添加依赖build.gridle中：

def room_version = "2.2.0-alpha01"
implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version"

定义一张数据表，这里id设置为逐渐且自动增长，就比较方便了。

//一张表
@Entity
public class Student {
    //主键唯一，自动增长
    @PrimaryKey(autoGenerate = true)
    private  int id;

    private String name;

    private int age;
    }

然后设置getter和setter的方法，以及带参数的构造方法，就是一个完整的表了：

package demo.demo.room;

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

//一张表
@Entity
public class Student {
    //主键唯一，自动增长
    @PrimaryKey(autoGenerate = true)
    private  int id;

    private String name;

    private int age;


    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

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

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

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

然后建立一个StudentDatabase抽象类，用于数据库的创建：

package demo.demo.room;

import android.content.Context;

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

@Database(entities = {Student.class}, version = 1, exportSchema = false)
public abstract class StudentDatabase extends RoomDatabase {
    //暴露Dao
    public abstract StudentDao getStudentDao();
    private static StudentDatabase INSTANCE;
    public static synchronized StudentDatabase getInstance(Context context){
        if(INSTANCE == null){
            INSTANCE = Room.databaseBuilder
                    (context.getApplicationContext(),
                    StudentDatabase.class, "student_database")
//                    .allowMainThreadQueries()
                    .build();
        }
        return INSTANCE;
    }
}

然后创建一个能对数据库进行增删改查的Dao接口:

package demo.demo.room;

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//对表操作，增删改查
public interface StudentDao {
    @Insert
    void insertStudents(Student...students);

    @Update
    void updateStudents(Student...students);

    //条件删除
    @Delete
    void deleteStudents(Student...students);

    //删除所有
    @Query("DELETE FROM Student")
    void deleteAllStudents();

    @Query("SELECT * FROM Student ORDER BY ID DESC")
    List<Student>getAllStudent();

}

最后就是编写数据库的引擎，具体对数据库进行操作，发挥实质性作用（采用异步操作）：

package demo.demo.room.manager;

import android.content.Context;
import android.os.AsyncTask;
import android.util.Log;

import java.util.List;

import demo.demo.room.Student;
import demo.demo.room.StudentDao;
import demo.demo.room.StudentDatabase;

public class DBEngine {
    private StudentDao studentDao;

    public DBEngine(Context context){
        StudentDatabase studentDatabase = StudentDatabase.getInstance(context);
        studentDao = studentDatabase.getStudentDao();
    }
    public void insertStudent(Student...students){
        new InsertAsyncTask(studentDao).execute(students);
    }

    public void updateStudents(Student...students){
        new UpdateAsyncTask(studentDao).execute(students);
    }

    public void deleteStudents(Student...students){
        new DeleteAsyncTask(studentDao).execute(students);
    }

    public void deleteAllStudents(){
        new DeleteAllAsyncTask(studentDao).execute();
    }

    public void queryAllStudents(){
        new QueryAllAsyncTask(studentDao).execute();
    }

    //异步
    static class UpdateAsyncTask extends AsyncTask<Student, Void, Void>{
        private StudentDao dao;
        public UpdateAsyncTask(StudentDao studentDao){
            dao = studentDao;
        }
        @Override
        protected Void doInBackground(Student... students) {
            dao.updateStudents(students);
            return null;
        }
    }

    //条件删除
    static class DeleteAsyncTask extends AsyncTask<Student, Void, Void>{
        private StudentDao dao;
        public DeleteAsyncTask(StudentDao studentDao){
            dao = studentDao;
        }
        @Override
        protected Void doInBackground(Student... students) {
            dao.deleteStudents(students);
            return null;
        }
    }

    //全部删除
    static class DeleteAllAsyncTask extends AsyncTask<Void, Void, Void>{
        private StudentDao dao;
        public DeleteAllAsyncTask(StudentDao studentDao){
            dao = studentDao;
        }
        @Override
        protected Void doInBackground(Void... voids) {
            dao.deleteAllStudents();
            return null;
        }
    }


    static class QueryAllAsyncTask extends AsyncTask<Void, Void, Void>{
        private StudentDao dao;
        public QueryAllAsyncTask(StudentDao studentDao){
            dao = studentDao;
        }
        @Override
        protected Void doInBackground(Void... students) {
            List<Student> allStudent = dao.getAllStudent();
            //遍历全部查询的结果
            for(Student student : allStudent){
                Log.e("Hunter", student.toString());
            }
            return null;
        }
    }

    static class InsertAsyncTask extends AsyncTask<Student, Void, Void>{
        private StudentDao dao;
        public InsertAsyncTask(StudentDao studentDao){
            dao = studentDao;
        }
        @Override
        protected Void doInBackground(Student... students) {
            dao.insertStudents(students);
            return null;
        }
    }
}

最后MainActivity进行引擎的调用，对数据库进行操作：

package demo.demo;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;

import demo.demo.room.Student;
import demo.demo.room.manager.DBEngine;

public class MainActivity extends AppCompatActivity {
    private DBEngine dbEngine;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        dbEngine = new DBEngine(this);
    }

    public void insertAction(View view) {
        Student student1 = new Student("hunter", 10);
        Student student2 = new Student("icy hunter", 10);
        dbEngine.insertStudent(student1, student2);
    }

    public void updateAction(View view) {
        Student student = new Student("hunterr", 20);
        //修改下标为23的
        student.setId(23);
        dbEngine.updateStudents(student);
    }

    public void deleteAction(View view) {
        Student student = new Student(null, 0);
        student.setId(23);
        dbEngine.deleteStudents(student);
    }

    public void queryAction(View view) {
        dbEngine.queryAllStudents();
    }

    public void deleteAllAction(View view) {
        dbEngine.deleteAllStudents();
    }
}

上面增删改查的操作和布局中的按钮绑定即可。

运行效果就如开局所示。