Paging 分页加载

1. build.gradle 添加引用库

    def paging_version = "3.1.1"
    // //google分页库 无感知预加载
    implementation "androidx.paging:paging-runtime:$paging_version"
    // alternatively - without Android dependencies for tests
    //testImplementation "androidx.paging:paging-common:$paging_version"

    def lifecycle_version = "2.6.0-alpha01"
    // ViewModel
    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_version"
    // ViewModel utilities for Compose
    //implementation "androidx.lifecycle:lifecycle-viewmodel-compose:$lifecycle_version"
    // Saved state module for ViewModel
    implementation "androidx.lifecycle:lifecycle-viewmodel-savedstate:$lifecycle_version"

    def room_version = "2.4.3"
    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"
    implementation "androidx.room:room-paging:$room_version"

2. 数据库管理

  2.1 Student.java

@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;
    }
}

  2.2 StudentDao.java

@Dao
public interface StudentDao {
    @Insert
    void insertStudents(Student... students);

    @Query("DELETE FROM student_table")
    void deleteAllStudents();

    @Query("SELECT * FROM student_table ORDER BY id")
    PagingSource<Integer, Student> getAllStudents();
    // DataSource.Factory<Integer, Student> getAllStudents();
}

  2.3 StudentsDatabase.java

@Database(entities = {Student.class}, version = 1, exportSchema = false)
public abstract class StudentsDatabase extends RoomDatabase {
    public static StudentsDatabase instance;

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

    public abstract StudentDao getStudentDao();
}

3. 创建列表视频器

  3.1 布局文件 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"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <TextView
        android:id="@+id/textView"
        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>

  3.2 MyPagedAdapter.java

public class MyPagedAdapter extends PagingDataAdapter<Student, MyPagedAdapter.MyViewHolder> {
    
    public 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 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);
        }
    }
}

4. 调用测试页

  4.1 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.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_clear"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="清空"
        app:layout_constraintBottom_toBottomOf="@+id/btn_populate"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/btn_populate"
        app:layout_constraintTop_toTopOf="@+id/btn_populate" />

    <Button
        android:id="@+id/btn_populate"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="生成"
        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" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        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.ConstraintLayout>

  4.2 MainActivity.xml

public class MainActivity extends AppCompatActivity {
    RecyclerView recyclerView;
    Button btnPopulate, btnClear;
    StudentDao studentDao;
    StudentsDatabase studentsDatabase;
    MyPagedAdapter pagedAdapter;
    LiveData<PagingData<Student>> allStudentsLivePaging;
    //LiveData<PagedList<Student>> allStudentsLivePaged;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        recyclerView = findViewById(R.id.recyclerView);
        pagedAdapter = new MyPagedAdapter();
        recyclerView.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));
        recyclerView.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL));
        recyclerView.setAdapter(pagedAdapter);
        studentsDatabase = StudentsDatabase.getInstance(this);
        studentDao = studentsDatabase.getStudentDao();

        //allStudentsLivePaging =   new LivePagedListBuilder<>(studentDao.getAllStudents(),30).build();
        //初始化配置,可以定义最大加载的数据量
        Pager<Integer, Student> pager = new Pager<>(new PagingConfig(20), () -> studentDao.getAllStudents());
        allStudentsLivePaging = PagingLiveData.getLiveData(pager);
        allStudentsLivePaging.observe(this, new Observer<PagingData<Student>>() {
            @Override
            public void onChanged(PagingData<Student> pagingData) {
                pagedAdapter.submitData(getLifecycle(), pagingData);

            }
        });

        btnPopulate = findViewById(R.id.btn_populate);
        btnClear = findViewById(R.id.btn_clear);
        btnPopulate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Student[] students = new Student[500];
                for (int i = 0; i < 500; i++) {
                    Student student = new Student();
                    student.setStudentNumber(i);
                    students[i] = student;
                }
                new InsertAsyncTack(studentDao).execute(students);
            }
        });

        btnClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                new ClearAsyncTack(studentDao).execute();
            }
        });
    }
    
    static class InsertAsyncTack extends AsyncTask<Student, Void, Void> {
        StudentDao studentDao;
        public InsertAsyncTack(StudentDao studentDao) {
            this.studentDao = studentDao;
        }
        @Override
        protected Void doInBackground(Student... students) {
            studentDao.insertStudents(students);
            return null;
        }
    }

    static class ClearAsyncTack extends AsyncTask<Void, Void, Void> {
        StudentDao studentDao;
        public ClearAsyncTack(StudentDao studentDao) {
            this.studentDao = studentDao;
        }
        @Override
        protected Void doInBackground(Void... voids) {
            studentDao.deleteAllStudents();
            return null;
        }
    }
}

5. 效果图