android Data Binding讲解二

第二节主要讲两点：1、观察者对象；2、动态绑定。

一、观察者对象：一个继承了BaseObservable的类，可以允许绑定一个监听器到附加对象上，这个对象可以监听到这个属性的变化。例子如下：

代码：

1、在要生成BR字段的属性的getter函数上加上@Bindable;

2、在setter函数里加上notifyPropertyChanged(BR.XXXX); BR.XXXX实在编译时生成的

public class User extends BaseObservable{
    private String name;
    private int age;
    private boolean isVisible=true;

    public User(String name,int age,boolean isVisible){
        this.name=name;
        this.age=age;
        this.isVisible=isVisible;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    @Bindable
    public boolean isVisible() {
        return isVisible;
    }

    public void setVisible(boolean visible) {
        isVisible = visible;
        //BR.visible在编译的时候生成
        notifyPropertyChanged(BR.visible);
    }

    public void setAge(int age) {
        this.age = age;
    }
}

布局文件：

1、用import引入对象，就可以在布局文件中访问这个对象，像在java中那样；

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">
    <data>
        <import type="android.view.View"/>
        <variable
            name="user"
            type="com.zfeng.databinding.User"/>
        <variable
            name="presenter"
            type="com.zfeng.databinding.MainPresenter"/>

    </data>
   
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal">
            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text='@{user.visible?"点击消失":"点击出来"}'
                android:onClick="@{()->presenter.clickVisible(user)}"/>
            <TextView
                android:id="@+id/main_tv"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="我是显示文字"
                android:visibility="@{user.visible?View.VISIBLE:View.GONE}"/>
        </LinearLayout>
</layout>

二、动态绑定

我们这里用RecyclerView来做例子。

代码：

1、与普通的Adapter相比唯一的不同是把ViewHolder中的view加入到DataBinding中。

public class MainAdapter extends RecyclerView.Adapter<MainAdapter.MainViewHolder>
{
    private Context context;
    private ArrayList<User > arrayList;

    public MainAdapter(Context context){
        arrayList=new ArrayList<>();

        for(int i=0;i<10;i++){
            User user=new User(i+"000",21,true);
            arrayList.add(user);
        }

        this.context=context;
    }

    @Override
    public MainAdapter.MainViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        View itemView=LayoutInflater.from(context)
                .inflate(R.layout.main_item,parent,false);
        MainViewHolder viewHolder=new MainViewHolder(itemView);

        return viewHolder;
    }

    @Override
    public void onBindViewHolder(MainAdapter.MainViewHolder holder, int position) {
        final User item=arrayList.get(position);
        holder.binding.setVariable(BR.user,item);
        holder.binding.executePendingBindings();
    }

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

    class MainViewHolder extends RecyclerView.ViewHolder
    {
        private MainItemBinding binding;

        public MainViewHolder(View view){
            super(view);
            binding=DataBindingUtil.bind(view);
        }
        public void binding(@NonNull User user){
            binding.setUser(user);
        }
    }
}

public class MainActivity extends AppCompatActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ActivityMainBinding binding= DataBindingUtil.setContentView(this,R.layout.activity_main);
        User user=new User("ZhaoFeng",28,true);
        MainPresenter presenter=new MainPresenter(this,user);
        binding.setUser(user);
        binding.setPresenter(presenter);

        binding.mainRecyclerview.setHasFixedSize(true);
        binding.mainRecyclerview.setLayoutManager(new LinearLayoutManager(this));
        binding.mainRecyclerview.setAdapter(new MainAdapter(this));

    }
}

布局文件：

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">
    <data>

    </data>
    <LinearLayout
        android:id="@+id/activity_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingBottom="@dimen/activity_vertical_margin"
        android:paddingLeft="@dimen/activity_horizontal_margin"
        android:paddingRight="@dimen/activity_horizontal_margin"
        android:paddingTop="@dimen/activity_vertical_margin"
        android:orientation="vertical">       
        <android.support.v7.widget.RecyclerView
            android:id="@+id/main_recyclerview"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"/>
    </LinearLayout>
</layout>

main_item.xml

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

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="15dip"
            android:text="@{user.name}"/>
    </LinearLayout>
</layout>

通过这些代码，itemview就会获得它响应的数据。

android Data Binding讲解二

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