paging架构
Jetpack 组件集

---

Paging

• 支持分页加载数据

• 支持有限或者无限的 数据源

• RecyclerView集成，提供PagedListAdapter

• LiveData 或者 RxJava 集成

---

使用

逻辑： RecyclerView --> PagedListAdapter --> PagedList --> LivePagedListBuilder --> DataSourceFactory --> Room Dao返回

• 搭配Room为数据源，在Dao中设计方法返回DataSource.Factory<Integer,Student>

• 使用RecyclerView 作为容器，设计类继承PagedListAdapter<Student,MyViewHolder>

• 此外使用AsyncTask来进行数据库操作或者联网操作

(其中的 Student 为Room 中 Entry类)

---

元素

---

DataSource

DataSource
DataSource.Factory Room 可直接返回该类型，提供数据库的DataSource

---

LivePagedListBuilder

接受 DataSourceFactory 和 pageSize 参数 返回一个 LiveData<PagedList<>>

---

PagedListAdapter

无论什么复杂的结构。1 . Adapter始终 输入数据 进行适配 2 . 注意泛型

获取 pagedList 提供给 RecyclerView 显示

submit方法提供 最新pagedList 数据

---

总结

code lab官方

---

代码

目录结构
MainActivity View层

public class MainActivity extends AppCompatActivity {

    RecyclerView recyclerView;
    Button btnGenerate, btnClear;
    StudentDao studentDao;
    StudentDatabase studentDatabase;
    MainPageAdapter mainPageAdapter;
    LiveData<PagedList<Student>> allStudentsLive;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mainPageAdapter = new MainPageAdapter();
        recyclerView = findViewById(R.id.recyclerView);
        btnGenerate = findViewById(R.id.btnGernerate);
        btnClear = findViewById(R.id.btnClear);

        recyclerView.setLayoutManager(new LinearLayoutManager(this, RecyclerView.VERTICAL, false));
        recyclerView.setAdapter(mainPageAdapter);
        studentDao = StudentDatabase.getInstance(this).getStudentDao();
        allStudentsLive = new LivePagedListBuilder<>(studentDao.getAllStudents(), 2).build();
        allStudentsLive.observe(this, new Observer<PagedList<Student>>() {
            @Override
            public void onChanged(final PagedList<Student> students) {
                mainPageAdapter.submitList(students);
                //  添加一些 callback 监听  数据的变化
                students.addWeakCallback(null, new PagedList.Callback() {
                    @Override
                    public void onChanged(int position, int count) {
                        Log.d("gongshijie", "此时的students数据：" + students + "count:" + count);
                    }

                    @Override
                    public void onInserted(int position, int count) {

                    }

                    @Override
                    public void onRemoved(int position, int count) {

                    }
                });
            }
        });

        btnGenerate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Student[] students = new Student[1000];
                for (int i = 0; i < 1000; i++) {
                    Student student = new Student();
                    student.setStudentNumber(i);
                    students[i] = student;
                }
                new InsertAsyncTask(studentDao).execute(students);
            }
        });

        btnClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new ClearAsyncTask(studentDao).execute();
            }
        });

    }


    static class InsertAsyncTask extends AsyncTask<Student, Void, Void> {
        StudentDao studentDao;

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

        @Override
        protected Void doInBackground(Student... students) {
            studentDao.insertStudents(students);
            return null;
        }
    }

    static class ClearAsyncTask extends AsyncTask<Void, Void, Void> {
        StudentDao studentDao;

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

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

Adapter层

public class MainPageAdapter extends PagedListAdapter<Student, MainPageAdapter.MyViewHolder> {


    protected MainPageAdapter() {
        super(new DiffUtil.ItemCallback<Student>() {
            @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 MainPageAdapter.MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater inflater = LayoutInflater.from(parent.getContext());
        View view = inflater.inflate(R.layout.item, parent, false);
        return new MyViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull MainPageAdapter.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);
        }
    }
}

StudentDao Room层

@Dao
public interface StudentDao {
    @Insert
    void insertStudents(Student ... students);
    @Query("DELETE FROM STUDENT_TABLE")
    void deleteAllStudent();
    @Query("SELECT * FROM STUDENT_TABLE ORDER BY ID")
    DataSource.Factory<Integer,Student> getAllStudents();
}

Room database

@Database(entities = {Student.class}, version = 1, exportSchema = false)
public abstract class StudentDatabase extends RoomDatabase {
    public abstract StudentDao getStudentDao();

    private static StudentDatabase INSTANCE;
    //双重检查  创建单例  支持并发   懒加载
    public static StudentDatabase getInstance(Context context) {
        if (INSTANCE == null) {
            synchronized (StudentDatabase.class) {
                if (INSTANCE == null) {
                    INSTANCE = Room.databaseBuilder(context.getApplicationContext(), StudentDatabase.class, "student_db").
                            build();
                }

            }
        }
        return INSTANCE;
    }
}

分析

pagesize == 1000
pagesize == 2 分享 成长