Android DataBinding使用详解（二）

《Android DataBinding使用详解（一）》

官方文档

Demo下载地址

1.在RecyclerView中使用DataBinding

Adapter的定义方式和普通方式相同，都是继承了RecyclerView.Adapter，然后实现其中的方法，但是具体的实现方式还是有所差别的：

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.BindingHolder> {    private List<RecyclerViewItem> list;    public RecyclerViewAdapter(List<RecyclerViewItem> list) {        this.list = list;    }    @Override    public RecyclerViewAdapter.BindingHolder onCreateViewHolder(ViewGroup parent, int viewType) {        AdapterRecyclerViewBinding binding = DataBindingUtil.inflate(                LayoutInflater.from(parent.getContext()), R.layout.adapter_recycler_view, parent, false);        BindingHolder holder = new BindingHolder(binding.getRoot());        holder.setBinding(binding);        return holder;    }    @Override    public void onBindViewHolder(RecyclerViewAdapter.BindingHolder holder, int position) {        holder.getBinding().setVariable(BR.item, list.get(position));        holder.getBinding().executePendingBindings();    }    @Override    public int getItemCount() {        return list.size();    }    public class BindingHolder extends RecyclerView.ViewHolder {        private AdapterRecyclerViewBinding binding;        public BindingHolder(View itemView) {            super(itemView);        }        public AdapterRecyclerViewBinding getBinding() {            return binding;        }        public void setBinding(AdapterRecyclerViewBinding binding) {            this.binding = binding;        }    }}

首先看下BindingHolder，由于使用了DataBinding机制，不需要在Holder中初始化控件了，只需要提供Binding的get和set方法就可以了：

public class BindingHolder extends RecyclerView.ViewHolder {    private AdapterRecyclerViewBinding binding;    public BindingHolder(View itemView) {        super(itemView);    }    public AdapterRecyclerViewBinding getBinding() {        return binding;    }    public void setBinding(AdapterRecyclerViewBinding binding) {        this.binding = binding;    }}

在onCreateViewHolder中绑定UI，获取到Binding对象，然后将Binding对象set到Holder中：

@Overridepublic RecyclerViewAdapter.BindingHolder onCreateViewHolder(ViewGroup parent, int viewType) {    AdapterRecyclerViewBinding binding = DataBindingUtil.inflate(            LayoutInflater.from(parent.getContext()), R.layout.adapter_recycler_view, parent, false);    BindingHolder holder = new BindingHolder(binding.getRoot());    holder.setBinding(binding);    return holder;}

在onBindViewHolder方法中，调用Binding的setVariable方法设置UI显示的数据，其中item是RecyclerView内置的变量，如果RecyclerView只使用了一种布局，还可以使用holder.getBinding().setItem(list.get(position));来设置数据。由于数据改变后，DataBinding会在下一帧刷新UI，这样会导致屏幕闪一下，所以还需要调用Binding的executePendingBindings方法立即刷新UI：

@Overridepublic void onBindViewHolder(RecyclerViewAdapter.BindingHolder holder, int position) {    holder.getBinding().setVariable(BR.item, list.get(position));    holder.getBinding().executePendingBindings();}

adapter_recycler_view布局文件：

<?xml version="1.0" encoding="utf-8"?><layout xmlns:android="http://schemas.android.com/apk/res/android">    <data>        <variable            name="item"            type="com.yl.databindingdemo.bean.RecyclerViewItem" />    </data>    <RelativeLayout        android:layout_width="match_parent"        android:layout_height="wrap_content">        <TextView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_centerInParent="true"            android:padding="10dp"            android:text="@{item.content}"            android:textColor="@color/colorAccent"            android:textSize="18sp" />    </RelativeLayout></layout>

在Activity中使用：

public class RecyclerViewActivity extends AppCompatActivity {    private List<RecyclerViewItem> list;    @Override    protected void onCreate(@Nullable Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        initData();        ActivityRecyclerViewBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_recycler_view);        binding.recyclerView.setLayoutManager(new LinearLayoutManager(this));        RecyclerViewAdapter recyclerViewAdapter = new RecyclerViewAdapter(list);        binding.recyclerView.setAdapter(recyclerViewAdapter);        // 更新        updateData();        recyclerViewAdapter.notifyDataSetChanged();    }    private void initData() {        list = new ArrayList<>();        for (int i = 0; i < 10; i++) {            list.add(new RecyclerViewItem(String.valueOf(i)));        }    }    private void updateData() {        for (int i = 10; i < 20; i++) {            list.add(new RecyclerViewItem(String.valueOf(i)));        }    }}

activity_recycler_view布局文件：

<?xml version="1.0" encoding="utf-8"?><layout xmlns:android="http://schemas.android.com/apk/res/android">    <data>    </data>    <LinearLayout        android:layout_width="match_parent"        android:layout_height="match_parent"        android:orientation="vertical">        <android.support.v7.widget.RecyclerView            android:id="@+id/recycler_view"            android:layout_width="match_parent"            android:layout_height="match_parent" />    </LinearLayout></layout>

2.在多布局RecyclerView中使用DataBinding

和普通的多布局Adapter类似，重写getItemViewType方法，然后在onCreateViewHolder方法中根据viewType加载相应的布局，onBindViewHolder方法中不需要再判断Holder类型，直接设置数据然后立即刷新UI即可：

public class MultiRecyclerViewAdapter extends RecyclerView.Adapter<MultiRecyclerViewAdapter.BindingHolder> {    private List<RecyclerViewItem> list;    public MultiRecyclerViewAdapter(List<RecyclerViewItem> list) {        this.list = list;    }    @Override    public int getItemViewType(int position) {        if (position < 5) {            return 0;        } else {            return 1;        }    }    @Override    public MultiRecyclerViewAdapter.BindingHolder onCreateViewHolder(ViewGroup parent, int viewType) {        ViewDataBinding binding;        if (viewType == 0) {            binding = DataBindingUtil.inflate(                    LayoutInflater.from(parent.getContext()), R.layout.adapter_recycler_view_other, parent, false);        } else {            binding = DataBindingUtil.inflate(                    LayoutInflater.from(parent.getContext()), R.layout.adapter_recycler_view, parent, false);        }        BindingHolder holder = new BindingHolder(binding.getRoot());        holder.setBinding(binding);        return holder;    }    @Override    public void onBindViewHolder(MultiRecyclerViewAdapter.BindingHolder holder, int position) {        holder.getBinding().setVariable(BR.item, list.get(position));        holder.getBinding().executePendingBindings();    }    @Override    public int getItemCount() {        return list.size();    }    public class BindingHolder extends RecyclerView.ViewHolder {        private ViewDataBinding binding;        public BindingHolder(View itemView) {            super(itemView);        }        public ViewDataBinding getBinding() {            return binding;        }        public void setBinding(ViewDataBinding binding) {            this.binding = binding;        }    }}

除此之外，还可以通过定义多个Holder的方式来实现。

3.自定义属性

举个栗子，如果你的项目中用到了Glide，或者是其他的图片加载框架，由于这些框架都是通过url给ImageView设置图片的，但是ImageView中并没有设置url的属性，那么该如何使用DataBinding绑定UI呢？这时DataBinding强大的自定义属性功能就派上用场了，一起来看看：

public class ImageUtils {    /**     * 加载图片     * 无需手动调用此方法     *     * @param view ImageView     * @param url  图片地址     */    @BindingAdapter({"imageUrl"})    public static void loadImage(ImageView view, String url) {        Glide.with(view.getContext()).load(url).into(view);    }}

使用@BindingAdapter注解设置自定义属性的名称，如上所示，imageUrl就是属性的名称，当ImageView中使用imageUrl属性时，会自动调用loadImage方法，参数view为当前使用imageUrl属性的View，参数url为图片地址。

布局文件：

<?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">    <data>        <variable            name="url"            type="String" />    </data>    <RelativeLayout        android:layout_width="match_parent"        android:layout_height="match_parent">        <!-- 当imageUrl存在时，会自动调用ImageUtils的loadImage方法 -->        <ImageView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_centerInParent="true"            app:imageUrl="@{url}" />    </RelativeLayout></layout>

Activity中使用：

public class CustomAttributeActivity extends AppCompatActivity {    @Override    protected void onCreate(@Nullable Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        ActivityCustomAttributeBinding binding = DataBindingUtil.setContentView(this,                R.layout.activity_custom_attribute);        binding.setUrl(null);    }}

4.ViewStub

在Android开发中，为了提高布局性能，经常使用ViewStub来动态显示UI，在DataBinding中也是支持使用ViewStub的，一起来学习下：

首先在布局文件中定义ViewStub，和普通方式相同：

<?xml version="1.0" encoding="utf-8"?><layout xmlns:android="http://schemas.android.com/apk/res/android">    <data>        <variable            name="clickListener"            type="android.view.View.OnClickListener" />    </data>    <LinearLayout        android:layout_width="match_parent"        android:layout_height="match_parent"        android:layout_margin="10dp"        android:orientation="vertical">        <ViewStub            android:id="@+id/view_stub"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout="@layout/layout_include" />        <Button            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_marginTop="10dp"            android:onClick="@{clickListener}"            android:text="显示ViewStub"            android:textAllCaps="false" />    </LinearLayout></layout>

在Activity中显示ViewStub：

public class ViewStubActivity extends AppCompatActivity {    @Override    protected void onCreate(@Nullable Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        final ActivityViewStubBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_view_stub);        binding.viewStub.setOnInflateListener(new ViewStub.OnInflateListener() {            @Override            public void onInflate(ViewStub stub, View inflated) {                LayoutIncludeBinding viewStubBinding = DataBindingUtil.bind(inflated);                User user = new User("容华", "谢后");                viewStubBinding.setUser(user);            }        });        binding.setClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                if (!binding.viewStub.isInflated()) {                    binding.viewStub.getViewStub().inflate();                }            }        });    }}

布局中的ViewStub控件在Binding中会被转换成代理类ViewStubProxy，所以需要调用代理类的getViewStub方法获取到ViewStub控件，然后再调用ViewStub控件的inflate方法显示布局，同时还需要监听ViewStub的OnInflateListener，当布局显示成功后调用DataBindingUtil的bind方法绑定数据。

看下效果：

OK，到这里DataBinding的大部分用法就讲完了，更多用法可以查看官方文档。

5.写在最后

源码已托管到GitHub上，欢迎Fork，觉得还不错就Start一下吧！

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