Data Binding实战（一）

Data Binding语法解析（二）

Data Binding高级用法（三）

好了，继前三篇学习了Data Binding之后，我们可以发现它的强大之处有这么几点：

1、使用MVVM模式，让整个项目结构清晰明了

2、通过ViewModel连接View和Model，使得View与Model层解耦，分层后各司其职，维护方便

3、易于项目的测试

4、可以根据id自动生成View的对象，再也不用findViewById了

好了，说了好处，当然也有不太好的地方，毕竟是今年刚刚推出来的，我总结出了两大缺点，我想以后的版本肯定会改进的：

1、Data Binding进行数据绑定时，不能通过代码提示写后续代码，全部都是需要一个一个手写，而且语法检查只在编译时检查，这个过程比较繁琐

2、Data Binding目前只有单向绑定，并不能双向的绑定，后续版本加上了双向绑定我想谁能拒绝用它呢

下面通过一个Demo来看Data Binding在RecyclerView中的使用：

Model层

就只有一个User类，它继承自BaseObservable，并在getter方法中加入@Bindable注解，在setter方法中加入notifyPropertyChanged()，这样User中的数据更新时可以通知UI更新：

public class User extends BaseObservable{
    private String userName;
    private String userPassword;
    private int userAge;
    @Bindable
    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
        notifyPropertyChanged(com.sunzxyong.binding.BR.userName);
    }
    @Bindable
    public String getUserPassword() {
        return userPassword;
    }

    public void setUserPassword(String userPassword) {
        this.userPassword = userPassword;
        notifyPropertyChanged(com.sunzxyong.binding.BR.userPassword);
    }
    @Bindable
    public int getUserAge() {
        return userAge;
    }

    public void setUserAge(int userAge) {
        this.userAge = userAge;
        notifyPropertyChanged(com.sunzxyong.binding.BR.userAge);
    }

    public User(String userName, String userPassword, int userAge) {
        this.userName = userName;
        this.userPassword = userPassword;
        this.userAge = userAge;
    }
}

View层

主界面：

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">

    <data>

    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        tools:context=".MainActivity">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="#03A9F4" />

        <android.support.v7.widget.RecyclerView
            android:id="@+id/recycler_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
    </LinearLayout>
</layout>

recycler_item：

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

    <data>
        <variable
            name="user"
            type="com.sunzxyong.binding.model.User"/>
    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_margin="5dp"
        android:background="#009688"
        android:gravity="center"
        android:orientation="vertical">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{user.userName}"
            android:textSize="20sp"
            android:textColor="#ffffff" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{user.userPassword}"
            android:textSize="20sp"
            android:textColor="#ffffff" />
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{String.valueOf(user.userAge)}"
            android:textSize="20sp"
            android:textColor="#ffffff" />
    </LinearLayout>
</layout>

recycler_item中绑定了User。。。

ViewModel层：

设置Toolbar和RecyclerView：

我们通过得到ActivityMainBinding对象得到Toolbar控件和RecyclerView控件：

//设置Toolbar
        ActivityMainBinding mainBinding = DataBindingUtil.setContentView(this, R.layout.activity_main);
        mainBinding.toolbar.setTitle("Android Data Binding代码实战");
        mainBinding.toolbar.setTitleTextColor(Color.WHITE);
        setSupportActionBar(mainBinding.toolbar);

        initData();

        //设置RecyclerView
        mainBinding.recyclerView.setLayoutManager(new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL));
        MyRecyclerViewAdapter adapter = new MyRecyclerViewAdapter(this,users);
        mainBinding.recyclerView.setAdapter(adapter);

BindingHolder：

public class BindingHolder extends RecyclerView.ViewHolder {
    private RecyclerItemBinding binding;

    public BindingHolder(View itemView) {
        super(itemView);
    }

    public RecyclerItemBinding getBinding() {
        return binding;
    }

    public void setBinding(RecyclerItemBinding binding) {
        this.binding = binding;
    }
}

MyRecyclerViewAdapter：

public class MyRecyclerViewAdapter extends RecyclerView.Adapter<BindingHolder> {
    private Context mContext;
    private List<User> users;
    private List<Integer> heights;
    public MyRecyclerViewAdapter(Context context,List<User> users) {
        this.mContext = context;
        this.users = users;
        initHeight();
    }
    private void initHeight(){
        heights = new ArrayList<>();
        for (int i = 0; i < users.size(); i++) {
            heights.add(200+(int)(300*Math.random()));
        }
    }
    @Override
    public BindingHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        RecyclerItemBinding mItemBinding = DataBindingUtil.inflate(LayoutInflater.from(mContext), R.layout.recycler_item, parent, false);
        BindingHolder mHolder = new BindingHolder(mItemBinding.getRoot());//得到根布局View设置给ViewHolder
        mHolder.setBinding(mItemBinding);//把mItemBinding设置给ViewHolder
        return mHolder;
    }

    @Override
    public void onBindViewHolder(BindingHolder holder, int position) {
        ViewGroup.LayoutParams params = holder.itemView.getLayoutParams();
        params.height = heights.get(position);
        holder.itemView.setLayoutParams(params);

        //通过holder.getBinding()得到Binding Class
        User user = users.get(position);
        holder.getBinding().setVariable(com.sunzxyong.binding.BR.user,user);//动态设置数据
//        holder.getBinding().setUser(user);这种方式也行，因为User继承自BaseObservable
        holder.getBinding().executePendingBindings();//立即更新UI
    }

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

效果：



源码地址

好了，Android Data Binding目前全部功能就讲完了

Google官方文档：https://developer.android.com/intl/zh-cn/tools/data-binding/guide.html