Android TV Leanback分析之ItemBridge

Leanback框架是基于RecyclerView，所以首先得了解RecyclerView的适配器。在这里，Leanback专门写了一个类ItemBridgeAdapter来适配数据

//########### 核心代码 ##########
public class ItemBridgeAdapter extends RecyclerView.Adapter implements FacetProviderAdapter {
  
    //ItemBridgeAdapter的ViewHolder是继承RecyclerView.ViewHolder的，将持有mPresenter、mHolder、mItem。可以在view的点击、选中监听事件中被传递出来。
    public static class ViewHolder extends RecyclerView.ViewHolder implements FacetProvider {
        final Presenter mPresenter;
        final Presenter.ViewHolder mHolder;
        Object mItem;
        Object mExtraObject;

        public final Presenter getPresenter() {
            return mPresenter;
        }

        public final Presenter.ViewHolder getViewHolder() {
            return mHolder;
        }

        public final Object getItem() {
            return mItem;
        }

        public final Object getExtraObject() {
            return mExtraObject;
        }

        public void setExtraObject(Object object) {
            mExtraObject = object;
        }

        @Override
        public Object getFacet(Class<?> facetClass) {
            return mHolder.getFacet(facetClass);
        }

        ViewHolder(Presenter presenter, View view, Presenter.ViewHolder holder) {
            super(view);
            mPresenter = presenter;
            mHolder = holder;
        }
    }
    //设置数据
    public void setAdapter(ObjectAdapter adapter) {
        if (adapter == mAdapter) {
            return;
        }
        if (mAdapter != null) {
            mAdapter.unregisterObserver(mDataObserver);
        }
        mAdapter = adapter;
        if (mAdapter == null) {
            notifyDataSetChanged();
            return;
        }
        //观察数据，ObjectAdapter的改变会更新到UI上
        mAdapter.registerObserver(mDataObserver);
        if (hasStableIds() != mAdapter.hasStableIds()) {
            setHasStableIds(mAdapter.hasStableIds());
        }
        notifyDataSetChanged();
    }

    @Override
    public int getItemViewType(int position) {
        //在获取getItemViewType时初始化每个item的presenter
        //PresenterSelector是一个presenter选择器，可以设置在自身ItemBridgeAdapter中，也可以设置ObjectAdapter中，优先使用自身的。
        PresenterSelector presenterSelector = mPresenterSelector != null
                ? mPresenterSelector : mAdapter.getPresenterSelector();
        //从ObjectAdapter获取到item
        Object item = mAdapter.get(position);
        //PresenterSelector通过item来获取具体的 presenter，
        Presenter presenter = presenterSelector.getPresenter(item);
        int type = mPresenters.indexOf(presenter);
        if (type < 0) {
          //存储每个type的presenter
            mPresenters.add(presenter);
            type = mPresenters.indexOf(presenter)；
            onAddPresenter(presenter, type);
            if (mAdapterListener != null) {
                mAdapterListener.onAddPresenter(presenter, type);
            }
        }
        return type;
    }

   @Override
    public final RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
       //通过type从存储的列表中拿到每个item的presenter
        Presenter presenter = mPresenters.get(viewType);
        Presenter.ViewHolder presenterVh;
        View view;
        //Wrapper 后面分析，此时不需要理会
        if (mWrapper != null) {
            view = mWrapper.createWrapper(parent);
            presenterVh = presenter.onCreateViewHolder(parent);
            mWrapper.wrap(view, presenterVh.view);
        } else {
            presenterVh = presenter.onCreateViewHolder(parent);
            view = presenterVh.view;
        }
       //ViewHolder将持有Presenter、view、Presenter. ViewHolder。
        ViewHolder viewHolder = new ViewHolder(presenter, view, presenterVh);
        //
        onCreate(viewHolder)；
        return viewHolder;
    }

   @Override
    public final void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if (DEBUG) Log.v(TAG, "onBindViewHolder position " + position);
        ViewHolder viewHolder = (ViewHolder) holder;
        //ViewHolder将持有Item。
        viewHolder.mItem = mAdapter.get(position);
        //执行Presenter的onBindViewHolder
        viewHolder.mPresenter.onBindViewHolder(viewHolder.mHolder, viewHolder.mItem);

        onBind(viewHolder);
        if (mAdapterListener != null) {
            mAdapterListener.onBind(viewHolder);
        }
    }

    @Override
    public final void onViewRecycled(RecyclerView.ViewHolder holder) {
        ViewHolder viewHolder = (ViewHolder) holder;
        //执行Presenter的onUnbindViewHolder
        viewHolder.mPresenter.onUnbindViewHolder(viewHolder.mHolder);
        onUnbind(viewHolder);
        if (mAdapterListener != null) {
            mAdapterListener.onUnbind(viewHolder);
        }
        viewHolder.mItem = null;
    }

在ItemBridgeAdapter提到了ObjectAdapter、Presenter、PresenterSelector 。ObjectAdapter提供数据，PresenterSelector根据每个item获取Presenter，Presenter来绑定item数据到ViewHolder中。