Android room操作数据库

1,在gradle中添加依赖:

def room_version = "2.2.0-rc01"
    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"

2,创建数据库

package com.example.pagingdemo;

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

@Entity(tableName = "student_table")
public class Student {
    @PrimaryKey(autoGenerate = true)
    private int id;
    @ColumnInfo(name = "student_number")
    private int studentNumber;

    public int getId() {
        return id;
    }

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

    public int getStudentNumber() {
        return studentNumber;
    }

    public void setStudentNumber(int studentNumber) {
        this.studentNumber = studentNumber;
    }
}

3,创建DAO

DAO，即数据访问接口。可以将SQL查询语句与方法相关联。

DAO必须是接口或抽象类。

package com.example.pagingdemo;

import androidx.lifecycle.LiveData;
import androidx.paging.DataSource;
import androidx.room.Dao;
import androidx.room.Insert;
import androidx.room.Query;

import java.util.List;

@Dao
public interface StudentDao {
//    插入
    @Insert
    void insertStudents(Student ...students);
//    清除
    @Query("DELETE FROM STUDENT_TABLE")
    void deleteAllStudents();
//    查询所有
    @Query("SELECT * FROM STUDENT_TABLE ORDER BY ID")
    LiveData> getAllStudentLive;
    //DataSource.Factory getAllstudents();
}

4,实现Room数据库

package com.example.pagingdemo;

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 StudentsDatabase extends RoomDatabase {
    private static StudentsDatabase instance;

    public synchronized static StudentsDatabase getInstance(Context context) {
        if(instance == null){
            instance = Room.databaseBuilder(context,StudentsDatabase.class,"students_database").build();
        }
        return instance;
    }

    abstract StudentDao getStudentDao();
}

5,RecyclerView提供

package com.example.pagingdemo;

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

import androidx.annotation.NonNull;
import androidx.paging.PagedListAdapter;
import androidx.recyclerview.widget.DiffUtil;
import androidx.recyclerview.widget.RecyclerView;

public class MyPagedAdapter extends PagedListAdapter {


    public MyPagedAdapter() {
        super(new DiffUtil.ItemCallback() {
            @Override
            public boolean areItemsTheSame(@NonNull Student oldItem, @NonNull Student newItem) {
                return oldItem.getId() == newItem.getId();
            }

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





    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        //创建视图
        LayoutInflater inflater = LayoutInflater.from(parent.getContext());
        View view=inflater.inflate(R.layout.cell,parent,false);
        return new MyViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
        Student student = getItem(position);
        if(student == null){
            holder.textView.setText("loading");
        }else{
            holder.textView.setText(String.valueOf(student.getStudentNumber()));
        }

    }

    static class MyViewHolder extends RecyclerView.ViewHolder{
        TextView textView;
        public MyViewHolder(@NonNull View itemView) {
            super(itemView);
            textView = itemView.findViewById(R.id.textView);
        }
    }
}

6,activity实现

package com.example.pagingdemo;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.Observer;
import androidx.paging.LivePagedListBuilder;
import androidx.paging.PagedList;
import androidx.paging.PagedListAdapter;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

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

public class MainActivity extends AppCompatActivity {
    RecyclerView recyclerView;
    Button buttonPopulate, buttonClear;
    StudentDao studentDao;
    StudentsDatabase studentsDatabase;
    MyPagedAdapter pagedAdapter;
    LiveData> allStudentsPaged;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //获取滚动列表,还有一个配套的adapter
        recyclerView = findViewById(R.id.recyclerView);
        pagedAdapter = new MyPagedAdapter();
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(pagedAdapter);
        studentsDatabase = StudentsDatabase.getInstance(this);
        studentDao = studentsDatabase.getStudentDao();
        allStudentsPaged = new LivePagedListBuilder<>(studentDao.getAllstudents(), 5).build();
        allStudentsPaged.observe(this, new Observer>() {
            @Override
            public void onChanged(PagedList students) {
                pagedAdapter.submitList(students);
            }
        });
        buttonPopulate = findViewById(R.id.buttonPopulate);
        buttonClear = findViewById(R.id.buttonClear);
        buttonPopulate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Student[] students = new Student[1000];
                for (int i = 0;i {
        StudentDao studentDao;
        //传入数据库操作
        public InsertAsyncTask(StudentDao studentDao) {
            this.studentDao = studentDao;
        }


        @Override
        protected Void doInBackground(Student... students) {
            studentDao.insertStudents(students);
            return null;
        }
    }
    //清空
    static class ClearAsyncTask extends AsyncTask{
        StudentDao studentDao;

        public ClearAsyncTask(StudentDao studentDao) {
            this.studentDao = studentDao;
        }


        @Override
        protected Void doInBackground(Void... voids) {
            studentDao.deleteAllStudents();
            return null;
        }
    }
}