Jetpack - Room&Paging
ROOM&Paging
- Room官方文档
- Paging官方文档
- 简单的使用
- ROOM
- Paging
Room官方文档
Room 持久性库在 SQLite 的基础上提供了一个抽象层，让用户能够在充分利用 SQLite 的强大功能的同时，获享更强健的数据库访问机制。
该库可帮助您在运行应用的设备上创建应用数据的缓存。此缓存充当应用的单一可信来源，使用户能够在应用中查看关键信息的一致副本，无论用户是否具有互联网连接。
Paging官方文档
分页库可帮助您一次加载和显示一小块数据。按需载入部分数据会减少网络带宽和系统资源的使用量
简单的使用
dependencies {
def room_version = "2.2.0-rc01"
implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version"
def paging_version = "2.1.0"
implementation "androidx.paging:paging-runtime:$paging_version"
}
ROOM
- Bean
import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;
@Entity
public class Student {
@PrimaryKey(autoGenerate = true)
public int id;
@ColumnInfo(name = "s_name") //数据库列名,不写就默认用字段名作为列名
private String name;
private int age;
private int s_num;//新增字段 ,学号 ,新增字段后数据库版本升为2,并写版本迁移sql
public Student(String name, int age, int s_num) {
this.name = name;
this.age = age;
this.s_num = s_num;
}
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;
}
public int getS_num() {
return s_num;
}
public void setS_num(int s_num) {
this.s_num = s_num;
}
}
- DAO
@Dao
public interface StudentDao {
@Insert
void insert(Student... students);
@Update
void updateStudent(Student... students);
@Delete
void deletec(Student student);
@Query("DELETE from Student")
void deleteAllStudent();
@Query("SELECT * FROM Student where s_name =(:name)")
Student queryStudentByName(String name);
//paging需要用到这种模式
@Query("SELECT * FROM Student order by id DESC")
DataSource.Factory getAllStudent();
@Query("SELECT * FROM Student order by id DESC")
LiveData> getAllListStudent();
@Query("SELECT * FROM Student order by id DESC")
List queryAllListStudent();
}
- Database
//数据库操作 ,这里可以多个Entity ,dao
/exportSchema 会生成一个json文件 记录sql语句的操作,需要在gradle配置文件路径
@Database(entities = {Student.class}, version = 2, exportSchema = false)
public abstract class MyDataBase extends RoomDatabase {
private static MyDataBase instance;
public static synchronized MyDataBase getInstance(Context context) {
if (instance == null) {
RoomDatabase.Builder builder = Room.databaseBuilder(context.getApplicationContext(), MyDataBase.class, "test");
//builder.fallbackToDestructiveMigration();//使用这个配置 ,数据库升级会清除以前的数据,重新建表
builder.addMigrations(MIGRATION_1_2, MIGRATION_2_3);//数据库升级
instance = builder.build();
}
return instance;
}
//提供学生的dao
public abstract StudentDao studentDao();
//数据库版本升级 , 数据迁移范例
static final Migration MIGRATION_1_2 = new Migration(1, 2) {
@Override
public void migrate(@NonNull SupportSQLiteDatabase database) {
database.execSQL("ALTER TABLE STUDENT ADD COLUMN S_NUM INTEGER NOT NULL DEFAULT 1");
}
};
static final Migration MIGRATION_2_3 = new Migration(2, 3) {
@Override
public void migrate(@NonNull SupportSQLiteDatabase database) {
//database.execSQL("");
}
};
}
- Repository
- 对数据库的操作都在这个类 ,增删改查
- 需要异步执行 ,room没有异步执行会抛异常(如需要在主线程执行,需要在database配置allowMainThreadQueries())
public class StudentRepository {
private final StudentDao studentDao;
private String TAG = "StudentRepository";
private LiveData> allListStudent;
public StudentRepository(Context context) {
MyDataBase instance = MyDataBase.getInstance(context);
studentDao = instance.studentDao();
allListStudent = studentDao.getAllListStudent();
}
public LiveData> getAllListStudent() {
return allListStudent;
}
public DataSource.Factory getAllStudent() {
return studentDao.getAllStudent();
}
public void insert(Student... students) {
Log.i(TAG, "insert: ");
new AsyncTaskInsert(studentDao).execute(students);
}
public void delete() {
new AsyncTaskDelete(studentDao).execute();
}
public void queryAll() {
new AsyncTaskQuery(studentDao).execute();
}
public void queryByName(Student student) {
new AsyncTaskQueryByName(studentDao).execute(student);
}
static class AsyncTaskInsert extends AsyncTask {
private StudentDao studentDao;
public AsyncTaskInsert(StudentDao studentDao) {
this.studentDao = studentDao;
}
@Override
protected Void doInBackground(Student... students) {
studentDao.insert(students);
return null;
}
}
static class AsyncTaskDelete extends AsyncTask {
private StudentDao studentDao;
public AsyncTaskDelete(StudentDao studentDao) {
this.studentDao = studentDao;
}
@Override
protected Void doInBackground(Void... voids) {
studentDao.deleteAllStudent();
return null;
}
}
static class AsyncTaskQuery extends AsyncTask {
private StudentDao studentDao;
private String TAG = "AsyncTaskQuery";
public AsyncTaskQuery(StudentDao studentDao) {
this.studentDao = studentDao;
}
@Override
protected Void doInBackground(Student... students) {
List list = studentDao.queryAllListStudent();
for (Student student : list) {
String name = student.getName();
int age = student.getAge();
Log.i(TAG, "Student -- name : " + name + " age : " + age);
}
return null;
}
}
static class AsyncTaskQueryByName extends AsyncTask {
private StudentDao studentDao;
private String TAG = "AsyncTaskQueryByName";
public AsyncTaskQueryByName(StudentDao studentDao) {
this.studentDao = studentDao;
}
@Override
protected Void doInBackground(Student... students) {
Student student = studentDao.queryStudentByName(students[0].getName());
String name = student.getName();
int age = student.getAge();
Log.i(TAG, "Student -- name : " + name + " age : " + age);
return null;
}
}
}
- RoomViewModel
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;
import androidx.paging.DataSource;
public class RoomViewModel extends AndroidViewModel {
private StudentRepository repository;
private String TAG = "RoomViewModel";
public RoomViewModel(@NonNull Application application) {
super(application);
repository = new StudentRepository(application.getApplicationContext());
}
public LiveData> getListStudent() {
Log.i(TAG, "getListStudent: ");
return repository.getAllListStudent();
}
private int size = 50;
public void insert() {
Student[] students = new Student[size];
Student student;
for (int i = 0; i < size; i++) {
student = new Student("张 " + i, 20 + i, i);
students[i] = student;
}
Log.i(TAG, "insert: ");
repository.insert(students);
}
public void delete() {
repository.delete();
}
public void queryAll() {
repository.queryAll();
}
public void queryByName(Student student) {
repository.queryByName(student);
}
public DataSource.Factory getAllStudent() {
return repository.getAllStudent();
}
}
Paging
- PagedListAdapter
import androidx.annotation.NonNull;
import androidx.paging.PagedListAdapter;
import androidx.recyclerview.widget.DiffUtil;
import androidx.recyclerview.widget.RecyclerView;
public class MyAdapter extends PagedListAdapter {
public MyAdapter() {
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.getAge() == newItem.getAge();
}
});
}
@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
LayoutInflater from = LayoutInflater.from(parent.getContext());
View view = from.inflate(R.layout.student, parent, false);
return new MyViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
Student item = getItem(position);
if (item == null) {
holder.textView.setText("加载中 ...");
} else {
holder.textView.setText(item.getName() + " ... " + item.getAge());
}
}
static class MyViewHolder extends RecyclerView.ViewHolder {
TextView textView;
public MyViewHolder(@NonNull View itemView) {
super(itemView);
textView = itemView.findViewById(R.id.textView_student);
}
}
}
- RecyclerView与Adapter绑定
XXXActivity{
...
...
...
myAdapter = new MyAdapter();
roomBinding.rv.setLayoutManager(new LinearLayoutManager(this));
roomBinding.rv.setAdapter(myAdapter);
pagedListLiveData = new LivePagedListBuilder<>(roomViewModel.getAllStudent(), 2).build();
pagedListLiveData.observe(this, new Observer>() {
@Override
public void onChanged(PagedList students) {
Log.i(TAG, "livedata onChanged: ");
//提交数据,更新界面
myAdapter.submitList(students);
students.addWeakCallback(null, new PagedList.Callback() {
@Override
public void onChanged(int position, int count) {
Log.i(TAG, "onChanged: position : "+position+" count : "+count);
}
@Override
public void onInserted(int position, int count) {
}
@Override
public void onRemoved(int position, int count) {
}
});
}
});
- XML