Android : Room 数据库的基本用法 _简单应用_二

1.导入依赖 build.gradle

dependencies {//Roomdef room_version = "2.5.0"implementation "androidx.room:room-runtime:$room_version"annotationProcessor "androidx.room:room-compiler:$room_version"// 使用androidx版本库  ViewModelProvidersimplementation 'androidx.lifecycle:lifecycle-extensions:2.1.0-alpha03'
}

2.PeopleDAtaBase.java 修改为单例：

package com.example.myroom.dao;import android.content.Context;import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;import com.example.myroom.entity.People;/** 优化 改成单例模式 singleton
抽象类 继承 RoomDatabase      我们不用实现people中的方法version = 1 版本号，exportSchema = false不允许导出数据库的架构*/
@Database(entities = {People.class}, version = 1, exportSchema = false)
public abstract class PeopleDataBase extends RoomDatabase {private static PeopleDataBase peopleDataBase;public static synchronized PeopleDataBase getPeopleDataBase(Context context){if(peopleDataBase == null){peopleDataBase = Room.databaseBuilder(context.getApplicationContext(),PeopleDataBase.class,"peopleDB")
// 默认不允许在主线程中连接数据库   在主线程中处理  使用了异步任务AsyncTask
//                    .allowMainThreadQueries().build();}return peopleDataBase;}/**
* Java 抽象类的一些特点
* 不能被实例化：抽象类不能被实例化，因为它没有具体的实现细节。它只能被继承，并且子类必须实现抽象类中的所有抽象方法。
* 包含抽象方法：抽象类可以包含抽象方法，这些方法只有声明但没有实现。子类必须实现这些抽象方法，否则它也必须被声明为抽象类。
* 提供通用功能和行为：抽象类提供了一些通用功能和行为，这些功能和行为可以被其子类继承和重用。子类可以根据需要扩展这些功能和行为，或者重写它们以提供不同的实现。
* 用于设计高层次的抽象：抽象类可以用于表示一个高层次的抽象概念或者一个通用模板，使得代码更加模块化和可维护。通过将一些公共方法和行为提取到一个抽象类中，可以避免在多个子类中重复实现相同的功能。
* 扩展性：抽象类可以定义一些扩展的接口，子类可以选择实现这些接口来提供额外的功能。这使得抽象类具有很好的扩展性，可以根据需要添加新的功能和行为
*/public abstract  PeopleDao peopleDao();}

3.添加异步任务 AsyncTask

3.1保存数据方法：InsertAsyncTask .java

package com.example.myroom.task;import android.os.AsyncTask;import com.example.myroom.dao.PeopleDao;
import com.example.myroom.entity.People;
/** AsyncTask 在 API 级别 30 中此字段已弃用 ， 请改用标准或 Kotlin 并发实用程序* 插入数据 异步任务*	android.os.AsyncTask<Params、进度、结果>* */
public class InsertAsyncTask extends AsyncTask<People,Void,Void> {/*** 4个步骤* 执行异步任务时，任务会经历 4 个步骤：** onPreExecute()，在任务之前的 UI 线程上调用 被执行。此步骤通常用于设置任务，例如 在用户界面中显示进度条。** doInBackground(Params)，在后台线程上调用 执行完毕后立即执行。* 此步骤用于 执行可能需要很长时间的后台计算。参数 的异步任务被传递到此步骤。* 计算结果必须 由此步骤返回，并将传递回最后一步。这一步 还可用于发布一个或多个单元 的进步。* 这些值在步骤中发布在 UI 线程上。onPreExecute()publishProgress(Progress)onProgressUpdate(Progress)** onProgressUpdate(Progress)，在 UI 线程上调用 调用 。* 执行的时间是 定义。此方法用于在用户中显示任何形式的进度 接口，而后台计算仍在执行。* 例如 它可用于对进度条进行动画处理或在文本字段中显示日志。publishProgress(Progress)** onPostExecute(Result)，在后台之后的 UI 线程上调用 计算完成。将后台计算的结果传递给主界面。* */private PeopleDao peopleDao;public InsertAsyncTask(PeopleDao peopleDao){this.peopleDao=peopleDao;}@Overrideprotected Void doInBackground(People... people) {//在后台执行 插入数据操作peopleDao.insertDataS(people);return null;}
}

3.2删除数据方法：DeleteAsyncTask .java

package com.example.myroom.task;import android.os.AsyncTask;import com.example.myroom.dao.PeopleDao;
import com.example.myroom.entity.People;public class DeleteAsyncTask extends AsyncTask<People,Void,Void> {private PeopleDao peopleDao;public DeleteAsyncTask(PeopleDao peopleDao){this.peopleDao = peopleDao;}@Overrideprotected Void doInBackground(People... people) {peopleDao.deleteDataS(people);return null;}
}

3.3 删除表数据方法 DeleteTBAsyncTask .java

package com.example.myroom.task;import android.os.AsyncTask;import com.example.myroom.dao.PeopleDao;public class DeleteTBAsyncTask extends AsyncTask<Void,Void,Void> {private PeopleDao peopleDao;public DeleteTBAsyncTask(PeopleDao peopleDao) {this.peopleDao = peopleDao;}@Overrideprotected Void doInBackground(Void... voids) {peopleDao.deleteTableData();return null;}
}

3.4 根据id查询数据方法 SelectByIdAsyncTask .java

package com.example.myroom.task;import android.os.AsyncTask;import com.example.myroom.dao.PeopleDao;
import com.example.myroom.entity.People;public class SelectByIdAsyncTask extends AsyncTask<Integer,Void,People> {private PeopleDao peopleDao;public SelectByIdAsyncTask(PeopleDao peopleDao) {this.peopleDao = peopleDao;}@Overrideprotected People doInBackground(Integer... integers) {People people =peopleDao.getPeople(integers[0]);return people;}
}

3.5 更新数据方法 UpdateAsyncTask .java

package com.example.myroom.task;import android.os.AsyncTask;import com.example.myroom.dao.PeopleDao;
import com.example.myroom.entity.People;public class UpdateAsyncTask extends AsyncTask<People,Void,Void> {private PeopleDao peopleDao;public UpdateAsyncTask( PeopleDao peopleDao){this.peopleDao = peopleDao;}@Overrideprotected Void doInBackground(People... people) {peopleDao.updateData(people);return null;}
}

4.修改PeopleDao.java

@Dao
public interface PeopleDao {...//查询 根据id倒序@Query("select * from people order by id desc")LiveData<List<People>> getPeopleLive(); //设置成为可以观察的数据 LiveDAta//    List<People> getPeoples();...
}

5.创建仓库 PeopleRepository.java

package com.example.myroom.dao;import android.content.Context;
import android.util.Log;import androidx.lifecycle.LiveData;import com.example.myroom.entity.People;
import com.example.myroom.task.DeleteAsyncTask;
import com.example.myroom.task.DeleteTBAsyncTask;
import com.example.myroom.task.InsertAsyncTask;
import com.example.myroom.task.SelectByIdAsyncTask;
import com.example.myroom.task.UpdateAsyncTask;import java.util.List;public class PeopleRepository {PeopleDao peopleDao;LiveData<List<People>> allPeopleLive;public PeopleRepository(Context context) {PeopleDataBase peopleDataBase = PeopleDataBase.getPeopleDataBase(context.getApplicationContext());peopleDao = peopleDataBase.peopleDao();allPeopleLive = peopleDao.getPeopleLive();}public LiveData<List<People>> getAllPeopleLive() {return allPeopleLive;}public void insertPeoples(People... people) {new InsertAsyncTask(peopleDao).execute(people);}public void updatePeoples(People... people) {new UpdateAsyncTask(peopleDao).execute(people);}public void deletePeople(People... people) {new DeleteAsyncTask(peopleDao).execute(people);}public void deleteTBPeoples() {new DeleteTBAsyncTask(peopleDao).execute();}public People selectPeopleById(Integer id) {People people = null;try {people = new SelectByIdAsyncTask(peopleDao).execute(id).get();} catch (Exception e) {Log.e("TAG", "根据id查询失败" + e.getMessage());}return people;}}

6.创建MyViewModel .java

package com.example.myroom;import android.app.Application;
import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;
import com.example.myroom.dao.PeopleDao;
import com.example.myroom.dao.PeopleRepository;
import com.example.myroom.entity.People;import java.util.List;//管理界面数据
public class MyViewModel extends AndroidViewModel {private PeopleDao peopleDao;private PeopleRepository peopleRepository;public MyViewModel(@NonNull Application application) {super(application);peopleRepository = new PeopleRepository(application);}public LiveData<List<People>> getAllPeopleLive() {return peopleRepository.getAllPeopleLive();}public void insertPeoples(People... people){peopleRepository.insertPeoples(people);}public void updatePeoples(People... people){peopleRepository.updatePeoples(people);}public void deletePeople(People... people){peopleRepository.deletePeople(people);
//        new DeleteAsyncTask(peopleDao).execute(people);}public void deleteTBPeoples(){peopleRepository.deleteTBPeoples();}public People selectPeopleById(Integer id){return peopleRepository.selectPeopleById(id);}}

7.MainActivity.java

package com.example.myroom;import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;
import com.example.myroom.dao.PeopleDao;
import com.example.myroom.dao.PeopleDataBase;
import com.example.myroom.entity.People;
import com.example.myroom.task.DeleteTBAsyncTask;import java.util.List;public class MainActivity extends AppCompatActivity {PeopleDataBase DB;PeopleDao peopleDao;MyViewModel myViewModel;private Button btnInsert, btnDelete, btnUpdate, btnSelect, btnDeleteData;private TextView textContent;private EditText etName, etAge, etSex, etSelect, etDelete, etUpdate;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);
//        binding = DataBindingUtil.setContentView(this,R.layout.activity_main);textContent = findViewById(R.id.tvcontent);etName = findViewById(R.id.etName);etAge = findViewById(R.id.etAge);etSex = findViewById(R.id.etSex);etSelect = findViewById(R.id.etSelect);etDelete = findViewById(R.id.etDelete);etUpdate = findViewById(R.id.etUpdate);btnInsert = findViewById(R.id.btnSave);btnDelete = findViewById(R.id.btnDelete);btnUpdate = findViewById(R.id.btnUpdate);btnSelect = findViewById(R.id.btnselect);btnDeleteData = findViewById(R.id.btnDeleteTB);myViewModel = ViewModelProviders.of(this).get(MyViewModel.class);DB = PeopleDataBase.getPeopleDataBase(this);peopleDao = DB.peopleDao();//观察数据myViewModel.getAllPeopleLive().observe(this, new Observer<List<People>>() {@Overridepublic void onChanged(List<People> peoples) {//内容发生改变执行执行下面代码StringBuilder text = new StringBuilder();for (int i = 0; i < peoples.size(); i++) {People people = peoples.get(i);text.append("id:").append(people.getId()).append("---name:").append(people.getName()).append("---age:").append(people.getAge()).append("---sex:").append(people.getSex()).append("\n");}textContent.setText(text.toString());}});
//        //查询数据
//        selectData(null);//按钮事件 插入数据btnInsert.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {//插入数据 防止空String name = etName.getText().toString().equals("") ? "张三" : etName.getText().toString();int age = etAge.getText().toString().equals("") ? 20 : Integer.parseInt(etAge.getText().toString());String sex = etSex.getText().toString().equals("") ? "男" : etSex.getText().toString();People people = new People(name, age, sex);myViewModel.insertPeoples(people);//                new InsertAsyncTask(peopleDao).execute(people);//                DB.peopleDao().insertDataS(people);//查询数据
//                selectData(null);}});//修改数据btnUpdate.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {//修改int id = etUpdate.getText().toString().equals("") ? 0 : Integer.parseInt(etUpdate.getText().toString());if (id != 0) {String name = etName.getText().toString();int age = Integer.parseInt(etAge.getText().toString());String sex = etSex.getText().toString();People people = new People(name, age, sex);people.setId(id);myViewModel.updatePeoples(people);//                    new UpdateAsyncTask(peopleDao).execute(people);
//                    DB.peopleDao().updateData(people);//查询
//                    selectData(null);}}});//删除btnDelete.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {int id = etDelete.getText().toString().equals("") ? 0 : Integer.parseInt(etDelete.getText().toString());if (id != 0) {People people = new People();people.setId(id);myViewModel.deletePeople(people);//                    new DeleteAsyncTask(peopleDao).execute(people);
//                    DB.peopleDao().deleteDataS(people);//查询
//                    selectData(null);}}});//根据id 查数据btnSelect.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {int id = etSelect.getText().toString().equals("") ? 0 : Integer.parseInt(etSelect.getText().toString());if (id != 0) {selectDataById(id);}}});//删除全部数据btnDeleteData.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {
//                DB.peopleDao().deleteTableData();new DeleteTBAsyncTask(peopleDao).execute();}});}/*** 查询数据的方法*/public void selectDataById(Integer id) {try {StringBuilder text = new StringBuilder();
//                People people = DB.peopleDao().getPeople(id);
//            People people = new SelectByIdAsyncTask(peopleDao).execute(id).get();People people = myViewModel.selectPeopleById(id);text.append("id:").append(people.getId()).append("---name:").append(people.getName()).append("---age:").append(people.getAge()).append("---sex:");textContent.setText(text.toString());} catch (Exception e) {Log.e("TAG", "----查询失败------------" + e.getMessage());}}}