Paging

Paging

• 添加paging和room的依赖

def paging_version = "3.0.1"
 
  implementation "androidx.paging:paging-runtime:$paging_version"
 
  // alternatively - without Android dependencies for tests
  testImplementation "androidx.paging:paging-common:$paging_version"
 
  // optional - RxJava2 support
  implementation "androidx.paging:paging-rxjava2:$paging_version"
 
  // optional - RxJava3 support
  implementation "androidx.paging:paging-rxjava3:$paging_version"
 
  // optional - Guava ListenableFuture support
  implementation "androidx.paging:paging-guava:$paging_version"
 
  // optional - Jetpack Compose integration
  implementation "androidx.paging:paging-compose:1.0.0-alpha12"

def room_version = "2.3.0"
 
    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"
 
    // optional - RxJava2 support for Room
    implementation "androidx.room:room-rxjava2:$room_version"
 
    // optional - RxJava3 support for Room
    implementation "androidx.room:room-rxjava3:$room_version"
 
    // optional - Guava support for Room, including Optional and ListenableFuture
    implementation "androidx.room:room-guava:$room_version"
 
    // optional - Test helpers
    testImplementation "androidx.room:room-testing:$room_version"
 
    // optional - Paging 3 Integration
    implementation "androidx.room:room-paging:2.4.0-alpha04"

• RecycleView的子布局cell.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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="wrap_content">
 
    <TextView
        android:id="@+id/tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:layout_marginBottom="8dp"
        android:text="TextView"
        android:textSize="24sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

• activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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=".MainActivity">
 
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@+id/guideline2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
 
    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.9" />
 
    <Button
        android:id="@+id/btn_load"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="加载"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/btn_clear"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="@+id/guideline2" />
 
    <Button
        android:id="@+id/btn_clear"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="清空"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/btn_load"
        app:layout_constraintTop_toTopOf="@+id/guideline2" />
</androidx.constraintlayout.widget.ConstraintLayout>

• Student.java

package com.example.paging;
 
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;
    }
}

• StudentDao.java

package com.example.paging;
 
import androidx.paging.DataSource;
import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;
 
@Dao
public interface StudentDao {
    @Insert
    void insertStudents(Student... students);
 
    @Query("DELETE FROM student_table")
    void deleteAllStudents();
 
    @Query("SELECT * FROM student_table ORDER BY id")
    DataSource.Factory<Integer, Student> getAllStudents();
}

• StudentDatabase.java

package com.example.paging;
 
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 StudentDatabase extends RoomDatabase {
    private static StudentDatabase studentDatabase;
    public static synchronized StudentDatabase getStudentDatabase(Context context) {
        if (studentDatabase == null){
            studentDatabase = Room.databaseBuilder(context, StudentDatabase.class, "student_database").build();
        }
        return studentDatabase;
    }
 
    abstract StudentDao getStudentDao();
}

• MyPagedAdapter.java

package com.example.paging;
 
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<Student, MyPagedAdapter.MyViewHolder> {
 
 
    protected MyPagedAdapter() {
        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 MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
        View view = layoutInflater.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.tv);
        }
    }
}

• MainActivity.java

package com.example.paging;
 
import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.Observer;
import androidx.paging.LivePagedListBuilder;
import androidx.paging.PagedList;
import androidx.recyclerview.widget.DividerItemDecoration;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
 
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
 
public class MainActivity extends AppCompatActivity {
 
    private RecyclerView recyclerView;
    private Button btn_load, btn_clear;
    private StudentDatabase studentDatabase;
    private StudentDao studentDao;
    private MyPagedAdapter myPagedAdapter;
    private LiveData<PagedList<Student>> allStudentsLivePaged;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        recyclerView = findViewById(R.id.rv);
        btn_load = findViewById(R.id.btn_load);
        btn_clear = findViewById(R.id.btn_clear);
        myPagedAdapter = new MyPagedAdapter();
 
        recyclerView.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));
        recyclerView.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL));
        recyclerView.setAdapter(myPagedAdapter);
 
        studentDatabase = StudentDatabase.getStudentDatabase(this);
        studentDao = studentDatabase.getStudentDao();
        // 参数2改小就能看到loading
        allStudentsLivePaged = new LivePagedListBuilder<>(studentDao.getAllStudents(), 20).build();
        allStudentsLivePaged.observe(this, new Observer<PagedList<Student>>() {
            @Override
            public void onChanged(PagedList<Student> students) {
                myPagedAdapter.submitList(students);
                students.addWeakCallback(null, new PagedList.Callback() {
                    @Override
                    public void onChanged(int i, int i1) {
                        Log.d("wmj", "onChanged: " + students);
                    }
 
                    @Override
                    public void onInserted(int i, int i1) {
 
                    }
 
                    @Override
                    public void onRemoved(int i, int i1) {
 
                    }
                });
            }
        });
 
        btn_load.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Student[] students = new Student[1000];
                for (int i = 0; i < 1000; i++) {
                    Student student = new Student();
                    student.setStudentNumber(i);
                    students[i] = student;
                }
                new InsertStudents(studentDao).execute(students);
            }
        });
 
        btn_clear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                new ClearStudents(studentDao).execute();
            }
        });
 
 
    }
 
 
    static class InsertStudents extends AsyncTask<Student, Void, Void>{
        StudentDao studentDao;
 
        public InsertStudents(StudentDao studentDao) {
            this.studentDao = studentDao;
        }
 
        @Override
        protected Void doInBackground(Student... students) {
            studentDao.insertStudents(students);
            return null;
        }
    }
 
    static class ClearStudents extends AsyncTask<Void, Void, Void>{
        StudentDao studentDao;
 
        public ClearStudents(StudentDao studentDao) {
            this.studentDao = studentDao;
        }
 
        @Override
        protected Void doInBackground(Void... voids) {
            studentDao.deleteAllStudents();
            return null;
        }
    }
}