Android学习笔记 46. Room

Android学习笔记

Android基础开发——数据存储

文章目录

- Android学习笔记
- - Android基础开发——数据存储
  - - 46. Room

46. Room

46.1 Room三角色介绍

→ → Room 是SQLite数据库的抽象

流畅易用的访问数据库。

Entity ：Student
DAO ：DAO
DB：StudentDatabase

注解

46.2 Room三角色编写

引入依赖

implementation 'androidx.room:room-runtime:2.4.3'
annotationProcessor 'androidx.room:room-compiler:2.4.3'
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同步

编写三角色

Student.java

package com.dingjiaxiong.room;


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

@Entity
public class Student {

    @PrimaryKey(autoGenerate = true)
    private int id;

    private String name;

    private int age;

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

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

    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 int getAge() {
        return age;
    }

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

package com.dingjiaxiong.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
public interface StudentDAO {

    //增
    @Insert
    void insertStudents(Student ... students);

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

    //删
    @Query("DELETE FROM Student")
    void deleteAllStudents();

    //查
    @Query("SELECT * FROM Student ORDER BY ID DESC")
    List<Student> getAllStudent();
}
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StudentDatabase.java

package com.dingjiaxiong.room;


import android.content.Context;

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

//数据库 关联
@Database(entities = {Student.class},version = 1,exportSchema = false)
public abstract class StudentDatabase extends RoomDatabase {


    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")
                    //默认异步线程
                    // .allowMainThreadQueries()
                    .build();
        }

        return INSTANCE;
    }



}
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46.3 Room实战

用户只需要拿DAO

布局


<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity2"
    android:orientation="vertical">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="插入"
        android:onClick="insertAction"
        />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="修改"
        android:onClick="updateAction"
        />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="删除"
        android:onClick="deleteAction"
        />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="查询"
        android:onClick="queryAction"
        />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="全部删除"
        android:onClick="deleteAllAction"
        />


LinearLayout>
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Student.java

package com.dingjiaxiong.room;


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

// 一张表（主键唯一 主键自动增长， name，age）
@Entity
public class Student {

    // 主键唯一  主键自动增长
    @PrimaryKey(autoGenerate = true)
    private int id;

    private String name;

    private int age;

    /*public Student() {
    }*/

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

    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 int getAge() {
        return age;
    }

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

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

package com.dingjiaxiong.room;


import android.content.Context;

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

//数据库 关联
@Database(entities = {Student.class},version = 1,exportSchema = false)
public abstract class StudentDatabase extends RoomDatabase {


    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")
                    //默认异步线程
                    .allowMainThreadQueries()
                    .build();
        }

        return INSTANCE;
    }



}
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StudentDao.java

package com.dingjiaxiong.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 // Database access object == 对表进行 增删改查
public interface StudentDao {

    // 增
    @Insert
    void insertStudents(Student ... students);

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

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

    // 删除 所有      @Delete 单个条件删除用的
    @Query("DELETE FROM Student")
    void deleteAllStudents();

    // 查询 所有  倒序 查询
    @Query("SELECT * FROM Student ORDER BY ID DESC")
    List<Student> getAllStudent();
}
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DBEngine.java

package com.dingjiaxiong.room.manager;

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

import com.dingjiaxiong.room.Student;
import com.dingjiaxiong.room.StudentDao;
import com.dingjiaxiong.room.StudentDatabase;

import java.util.List;

// DB的引擎
public class DBEngine {

    // 只需要拿到dao，就能够对数据库 增删改查了
    private StudentDao studentDao;

    public DBEngine(Context context) {
        StudentDatabase studentDatabase = StudentDatabase.getInstance(context);
        studentDao = studentDatabase.getStudentDao();
    }

    // dao 增删改查

    // insert 插入
    public void insertStudents(Student... students) {
        new InsertAsyncTask(studentDao).execute(students);
    }

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

    // delete 删除 条件
    public void deleteStudents(Student... students) {
        new DeleteAsyncTask(studentDao).execute(students);
    }

    // delete 全部删除
    public void deleteAllStudents() {
        new DeleteAllAsyncTask(studentDao).execute();
    }

    // 查询全部
    public void queryAllStudents() {
        new QueryAllAsyncTask(studentDao).execute();
    }

    // 如果我们想玩数据库 默认是异步线程  ============  异步操作

    // insert 插入
    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;
        }
    }

    // update 更新
    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;
        }
    }

    // delete 删除 条件
    static class DeleteAsyncTask extends AsyncTask<Student, Void, Void> {

        private StudentDao dao;

        public DeleteAsyncTask(StudentDao studentDao) {
            dao = studentDao;
        }

        @Override
        protected Void doInBackground(Student... students) { // 既然传递了 student 进来，就是条件删除
            dao.deleteStudents(students);
            return null;
        }
    }

    // 删除 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;
        }
    }

    // 全部 查询
    private static class QueryAllAsyncTask extends AsyncTask<Void, Void, Void> {

        private StudentDao dao;

        public QueryAllAsyncTask(StudentDao studentDao) {
            dao = studentDao;
        }

        @Override
        protected Void doInBackground(Void... voids) {
            List<Student> allStudent = dao.getAllStudent();

            // 遍历全部查询的结构
            for (Student student : allStudent) {
                Log.e("Derry", "doInBackground: 全部 查询 每一项：" + student.toString() );
            }

            return null;
        }
    }

}
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MainActivity2.java

package com.dingjiaxiong.mysqlite;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;

import com.dingjiaxiong.room.Student;
import com.dingjiaxiong.room.manager.DBEngine;


// Room 的学习
public class MainActivity2 extends AppCompatActivity {

    private DBEngine dbEngine;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        dbEngine = new DBEngine(this);
    }

    /**
     * 插入
     * @param view
     */
    public void insertAction(View view) {
        Student student1 = new Student("张三", 20);
        Student student2 = new Student("李四", 23);
        Student student3 = new Student("王五", 27);
        dbEngine.insertStudents(student1, student2, student3);
    }

    /**
     * 修改  下标为 3   修改成："李元霸", 40
     * @param view
     */
    public void updateAction(View view) {
        Student student = new Student("李元霸", 40);
        student.setId(3);
        dbEngine.updateStudents(student);
    }

    /**
     * 删除 条件 下标为 3
     * @param view
     */
    public void deleteAction(View view) {
        Student student = new Student(null, 0);
        student.setId(3);
        dbEngine.deleteStudents(student);
    }

    /**
     * 查询
     * @param view
     */
    public void queryAction(View view) {
        dbEngine.queryAllStudents();
    }

    /**
     * 全部 删除
     * @param view
     */
    public void deleteAllAction(View view) {
        dbEngine.deleteAllStudents();
    }
}
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运行

在这里插入图片描述

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原文地址：https://blog.csdn.net/weixin_44226181/article/details/126314420