Android Data Binding

Data Binding官方文档
Data Binding官方文档-翻译
Data Binding官方文档-实例

1. 基本结构

1.1 JavaBeans对象

public class User {
   private final String firstName;
   public User(String firstName) {
       this.firstName = firstName;
   }
   public String getFirstName() {
       return this.firstName;
   }
}

1.2 布局文件

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">
   <data>
       <variable name="user" type="com.example.User"/>
   </data>
   <LinearLayout
       android:orientation="vertical"
       android:layout_width="match_parent"
       android:layout_height="match_parent">
       <TextView android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:text="@{user.firstName}"/>
   </LinearLayout>
</layout>

1.3 Activity

@Override
protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.main_activity);
   User user = new User("Test");
   binding.setUser(user);
}

以上三步完成了基本数据绑定

2. 动态更新

当JavaBean对象的数据发生变化时，View自动更新。
正常的数据源只能作到绑定，想要动态更新，就必需要用Observable的方式存储数据，如下是实现Observable的三种方式。

2.1 Observable 对象

实现android.databinding.Observable或继承其实现类

private static class User extends BaseObservable {
   private String firstName;
   @Bindable
   public String getFirstName() {
       return this.firstName;
   }
   public void setFirstName(String firstName) {
       this.firstName = firstName;
       notifyPropertyChanged(BR.firstName);
   }
}

2.2 Observable 字段

基本的数据类型都有相应的Observable类

public final ObservableField<String> firstName = new ObservableField<>();

2.3 Observable 集合

ObservableArrayMap<String, Object> mapUser = new ObservableArrayMap<>();
user.put("firstName", "Google");

2.4 引用

不管是对象、字段仍是集合，都是以Observable的方式存储数据。接下来就是在布局中引用了。

<layout xmlns:android="http://schemas.android.com/apk/res/android">
    <data>
        <import type="android.databinding.ObservableMap" />
        <variable name="user" type="com.example.ObservableUser" />
        <variable name="firstName" type="android.databinding.ObservableField" />
        <variable name="mapUser" type="ObservableMap&lt;String, Object>" />
    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <!-- Observable 对象 -->
        <TextView
            android:text="@{user.firstName}"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

        <!-- Observable 字段 -->
        <TextView
            android:text="@{firstName.get()}"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

        <!-- Observable 集合 -->
        <TextView
            android:text="@{mapUser[`firstName`]}"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

    </LinearLayout>
</layout>

3. RecyclerView动态绑定

private static class RecyclerViewAdapter
        extends RecyclerView.Adapter<RecyclerViewAdapter.BindingHolder> {

    private List<Model> mModels;

    public static class BindingHolder extends RecyclerView.ViewHolder {
        private final ViewDataBinding binding;

        public BindingHolder(ViewDataBinding binding) {
            super(binding.getRoot());
            this.binding = binding;
            // 这里能够binding.getRoot().findViewById，而后再onBindViewHolder中绑定事件，目前没有找到更方便的方法
        }

        public ViewDataBinding getBinding() {
            return binding;
        }
    }

    @Override
    public BindingHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        ViewDataBinding binding = DataBindingUtil.inflate(
                LayoutInflater.from(parent.getContext()),
                R.layout.list_item,
                parent,
                false);

        BindingHolder holder = new BindingHolder(binding);

        return holder;
    }

    @Override
    public void onBindViewHolder(final BindingHolder holder, int position) {
        final Model model = mModels.get(position);

        holder.getBinding().setVariable(BR.model, model);
        holder.getBinding().getRoot().setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

            }
        });
        holder.getBinding().executePendingBindings();
    }

    @Override
    public int getItemCount() {
        return mModels.size();
    }

}