question: public < F > void addViewType ( Class < ? extends F > clazz , ViewHolderFactory < ? extends ViewHolder < ? extends F > > factory ) { int id = mViewHolderFactoryRegistry . size ( ) ; mViewHolderTypeRegistry . put ( clazz , id ) ; mViewHolderFactoryRegistry . put ( id , factory ) ; }
target:  Register different type of data with different ViewHolder using ViewHolderFactory.