本篇给出数据绑定及MVVM框架的总结，主要内容来自《Android编程权威指南》。

MVVM：Model-View-ViewModel，将其中的View的状态和行为抽象化，将视图UI和业务逻辑分开。MVVM架构很好地把控制器里的臃肿代码抽到布局文件里，让开发人员很容易看出哪些是动态界面。同时，它抽出部门动态控制器代码放入ViewModel类，方便开发测试和验证。

 

DataBinding：一个帮助开发者处理视图与数据交互的工具，即数据绑定。

gradle——Android添加

dataBinding {     enabled = true }

把一般布局改造为数据绑定布局

<layout>标签告诉数据绑定工具处理此类，数据绑定工具会自动生成一个绑定类，默认以布局文件命名，如fragment_beat_box.xml绑定类为FragmentBeatBoxBinding。实例化视图层级结构时，实例化FragmentBeatBoxBinding，其getRoot()引着布局视图结构，该类也会引着布局文件里以android:id标签引用的其他视图。

public class BeatBoxFragment extends Fragment {    private BeatBox mBeatBox;    public static BeatBoxFragment newInstance() {        return new BeatBoxFragment();    }    @Override    public void onCreate(@Nullable Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        mBeatBox = new BeatBox(getActivity());    }    @Nullable    @Override    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {        FragmentBeatBoxBinding binding = DataBindingUtil.inflate(inflater, R.layout.fragment_beat_box, container, false);        binding.recyclerView.setLayoutManager(new GridLayoutManager(getActivity(),3));        binding.recyclerView.setAdapter(new SoundAdapter(mBeatBox.getSounds()));        return binding.getRoot();    }    private class SoundHolder extends RecyclerView.ViewHolder {        private ListItemSoundBinding mBinding;        private SoundHolder(ListItemSoundBinding binding) {            super(binding.getRoot());            mBinding = binding;            mBinding.setViewModel(new SoundViewModel(mBeatBox));        }        public void bind(Sound soud) {            mBinding.getViewModel().setSound(soud);            mBinding.executePendingBindings();        }    }    private class SoundAdapter extends RecyclerView.Adapter
     
       {        private List
      
        mSounds;        public SoundAdapter(List
       
         sounds) {            mSounds = sounds;        }        @Override        public SoundHolder onCreateViewHolder(ViewGroup parent, int viewType) {            LayoutInflater inflater = LayoutInflater.from(getActivity());            ListItemSoundBinding binding = DataBindingUtil.inflate(inflater, R.layout.list_item_sound, parent, false);            return new SoundHolder(binding);        }        @Override        public void onBindViewHolder(SoundHolder holder, int position) {            Sound sound = mSounds.get(position);            holder.bind(sound);        }        @Override        public int getItemCount() {            return mSounds.size();        }    }}
       
      
     

视图模型

public class SoundViewModel extends BaseObservable {    private Sound mSound;    private BeatBox mBeatBox;    public SoundViewModel(BeatBox beatBox) {        mBeatBox = beatBox;    }    @Bindable    public String getTitle() {        return mSound.getName();    }    public Sound getSound() {        return mSound;    }    public void setSound(Sound sound) {        mSound = sound;        notifyChange();    }}

notifyChange()通知绑定类，视图模型对象上所有可绑定属性都已经更新，绑定类会再次运行绑定表达式更新视图数据。setSound(sound)方法一被调用，ListItemSoundBinding就立即知道，并调用list_item_sound.xml布局里指定的Button.setText(String)方法。viewModel.title就是viewModel.getTitle()简写形式。

 完整项目