本文目录 ⌄
本文目的：记录使用DataBinding实现对拥有RecyclerView组件的页面进行较大程度的解耦的方式。
RecyclerView数据源：从本地SQLite数据库中使用Room获取一个LiveData并存储在ViewModel中：
public class StudentViewModel extends AndroidViewModel {
private StudentRepository repository;
private LiveData<List<Student>> studentsLD;
public StudentViewModel(@NonNull Application application) {
super(application);
this.repository=new StudentRepository(application);
studentsLD=repository.getAllStudentsLive();
}
public void insert(){
Student s1=new Student("jack",18);
Student s2=new Student("rose",17);
insertStudents(s1,s2);
}
public void update(){
Student s1=new Student(3,"jason",20);
updateStudents(s1);
}
public void clear(){
deleteAllStudents();
}
public void delete(){
Student s1=new Student(2,"rose",17);
deleteStudents(s1);
}
private void insertStudents(Student... students){
repository.insertStudents(students);
}
private void updateStudents(Student... students){
repository.updateStudents(students);
}
private void deleteStudents(Student... students){
repository.deleteStudents(students);
}
private void deleteAllStudents(){
repository.deleteAllStudents();
}
// 错误！！！
// public LiveData<List<Student>> getAllStudentLive(){
// return repository.getAllStudentsLive();
// }
// 正确
public LiveData<List<Student>> getStudentsLD() {
return studentsLD;
}
}将获取到的LiveData<List<Student>>对象通过DataBinding传给Activity的xml布局中：
<?xml version="1.0" encoding="utf-8"?>
<layout 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">
<data>
<variable
name="viewModel"
type="com.shopkeeper.room2.StudentViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="60dp"
android:text="增加"
android:onClick="@{()->viewModel.insert()}"
app:layout_constraintBottom_toBottomOf="@+id/button2"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="@+id/button2" />
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="60dp"
android:layout_marginEnd="60dp"
android:text="删除"
android:onClick="@{()->viewModel.delete()}"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/button3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="60dp"
android:text="修改"
android:onClick="@{()->viewModel.update()}"
app:layout_constraintEnd_toEndOf="@+id/button"
app:layout_constraintStart_toStartOf="@+id/button"
app:layout_constraintTop_toBottomOf="@+id/button" />
<Button
android:id="@+id/button4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="清空"
android:onClick="@{()->viewModel.clear()}"
app:layout_constraintBottom_toBottomOf="@+id/button3"
app:layout_constraintEnd_toEndOf="@+id/button2"
app:layout_constraintStart_toStartOf="@+id/button2"
app:layout_constraintTop_toTopOf="@+id/button3" />
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recycleView"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginTop="30dp"
app:studentBinder="@{viewModel.studentsLD}"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/button3" />
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>此处定义了一个studentBinder的BindingAdapter，用于处理传递过来的数据：
public class RVAdapter {
@BindingAdapter("studentBinder")
public static void studentsBindAdapter(RecyclerView recyclerView, List<Student> students){
StudentAdapter adapter = (StudentAdapter) recyclerView.getAdapter();
assert adapter != null;
adapter.setStudents(students);
}
}由于绑定的是LiveData数据，所以每当列表发生改变时，就会自动执行BindingAdapter中的方法，进而通过RecyclerView的Adapter更新并显示数据（每一个Item也是通过DataBinding来绑定数据的）。Adapter内容：
public class StudentAdapter extends RecyclerView.Adapter<StudentAdapter.StudentViewHolder> {
List<Student> students;
public StudentAdapter(List<Student> students) {
this.students = students;
}
@NonNull
@Override
public StudentViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
ItemBinding binding= DataBindingUtil.inflate(LayoutInflater.from(parent.getContext()),R.layout.item,parent,false);
return new StudentViewHolder(binding);
}
@Override
public void onBindViewHolder(@NonNull StudentViewHolder holder, int position) {
holder.binding.setStudent(students.get(position));
}
@Override
public int getItemCount() {
return students==null?0:students.size();
}
static class StudentViewHolder extends RecyclerView.ViewHolder{
ItemBinding binding;
public StudentViewHolder(@NonNull ItemBinding binding) {
super(binding.getRoot());
this.binding=binding;
}
}
public void setStudents(List<Student> students) {
this.students = students;
notifyDataSetChanged();
}
}通过这种写法，在Activity中的代码量就很少了，甚至不需要使用Observer来监听LiveData的数据变化：
public class MainActivity extends AppCompatActivity {
ActivityMainBinding binding;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
binding= DataBindingUtil.setContentView(this,R.layout.activity_main);
StudentViewModel viewModel = new ViewModelProvider(this,
new ViewModelProvider.AndroidViewModelFactory(getApplication()))
.get(StudentViewModel.class);
binding.recycleView.setAdapter(new StudentAdapter(viewModel.getStudentsLD().getValue()));
binding.recycleView.setLayoutManager(new LinearLayoutManager(this));
binding.setViewModel(viewModel);
binding.setLifecycleOwner(this);
}
}效果图：