简介
RecyclerView是我们开发过程中经常使用到的一个元素，原生的RecyclerView.Adapter基本上可以满足一般的需求，关于RecyclerView的基础介绍请移步：
关于多类型的Item,原生的Adapter可以通过getItemViewType返回对应的ViewHolder类型，然后在onCreateViewHolder传入的type参数，生成不同的ViewHolder，更要命的是数据绑定过程中onBindViewHolder只传入ViewHolder对象和position，针对不同的ViewHolder，我们只能通过instanceof和强制类型装换来对不同的ViewHolder进行不同的数据操作。
这样做的弊端就是，后续如果需要添加一个类型，几乎需要修改Adapter类中的每一个方法，不利于维护。
类结构
目的
- 便于维护。增删Item的类型不需要修改Adapter的代码；
- 条例清晰。不同类型的Item对应不同的Bean类，对应不用的ViewHolder,对应不同的layout item type <—-> layout <—> ViewHolder <—-> java bean
- 工厂接口。抽象出TypeFactory接口，针对同一个Bean,可以使用不同的layout和不同的ViewHolder。
思路
- 所有Bean类实现统一Visitable接口，实现type方法，返回对应的layout id;
- 创建BaseViewHolder使用泛型，T为Bean类。使用SparseArray存储View,View的id作为唯一标识。
- 具体的ViewHolder类，继承BaseViewHolder,传入不同的Bean类，方便不同的ViewHolder中绑定不同的数据。
- Adapter实现中使用Visitable List同一处理列表数据，使用事项TypeFactory接口的实例返回ItemType，viewHolder等
代码结构
代码内容
Visitable接口
public interface Visitable { int type(TypeFactory typeFactory);} TypeFactory接口
public interface TypeFactory { int type(BannerBean bannerBean); int type(ContentBean contentBean); int type(SearchBean searchBean); int type(DividerBean dividerBean); BaseViewHolder createViewHolder(int type, View itemView);} BaseViewHolder抽象类
public abstract class BaseViewHolderextends RecyclerView.ViewHolder{ SparseArray mViews; View mItemView; public BaseViewHolder(View itemView) { super(itemView); mItemView = itemView; mViews = new SparseArray<>(); } public View getView(int resId) { View view = mViews.get(resId); if(view== null) { view = mItemView.findViewById(resId); mViews.put(resId, view); } return view; } public abstract void bindViewData(T data);}
TypeFactory实现类~ItemTypeFactory
public class ItemTypeFactory implements TypeFactory { public static final int BANNER_ITEM_LAYOUT = R.layout.rv_item_banner; public static final int CONTENT_ITEM_LAYOUT = R.layout.rv_item_content; public static final int SEARCH_ITEM_LAYOUT = R.layout.rv_item_search; public static final int DIVIDER_ITEM_LAYOUT = R.layout.rv_item_divider; @Override public int type(BannerBean bannerBean) { return BANNER_ITEM_LAYOUT; } @Override public int type(ContentBean contentBean) { return CONTENT_ITEM_LAYOUT; } @Override public int type(DividerBean dividerBean){ return DIVIDER_ITEM_LAYOUT; } @Override public int type(SearchBean dividerBean){ return SEARCH_ITEM_LAYOUT; } @Override public BaseViewHolder createViewHolder(int type, View itemView) { switch (type) { case BANNER_ITEM_LAYOUT: return new BannerViewHolder(itemView); case SEARCH_ITEM_LAYOUT: return new SearchViewHolder(itemView); case CONTENT_ITEM_LAYOUT: return new ContentViewHolder(itemView); case DIVIDER_ITEM_LAYOUT: return new DividerViewHolder(itemView); default: return null; } }} 各种Java Bean类
BannerBean
public class BannerBean implements Visitable { int[] mResIds; public BannerBean(int[] mResIds) { this.mResIds = mResIds; } public int[] getmResIds() { return mResIds; } public void setmResIds(int[] mResIds) { this.mResIds = mResIds; } @Override public int type(TypeFactory typeFactory) { return typeFactory.type(this); }} ContentBean
public class ContentBean implements Visitable{ String content; public String getContent() { return content; } public void setContent(String content) { this.content = content; } public ContentBean(String content) { this.content = content; } @Override public int type(TypeFactory typeFactory) { return typeFactory.type(this); }} DividerBean
public class DividerBean implements Visitable{ @Override public int type(TypeFactory typeFactory) { return typeFactory.type(this); }} SearchBean
public class SearchBean implements Visitable { @Override public int type(TypeFactory typeFactory) { return typeFactory.type(this); }} MultiRecyclerAdapter
public class MultiRecyclerAdapter extends RecyclerView.Adapter{ List mData; TypeFactory typeFactory; public MultiRecyclerAdapter(List mData) { this.mData = mData; this.typeFactory = new ItemTypeFactory(); } @Override public BaseViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view = LayoutInflater.from(parent.getContext()).inflate(viewType, parent, false); return typeFactory.createViewHolder(viewType, view); } @Override public void onBindViewHolder(BaseViewHolder holder, int position) { holder.bindViewData(mData.get(position)); } @Override public int getItemViewType(int position) { return mData.get(position).type(typeFactory); } @Override public int getItemCount() { return (mData != null ? mData.size() : 0); }}
示例
public class MultiActivity extends AppCompatActivity { @BindView(R.id.rv_content) RecyclerView rvContent; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_weather); ButterKnife.bind(this); List beans = new ArrayList<>(); int[] resIds = {R.mipmap.banner_one, R.mipmap.banner_two, R.mipmap.banner_three, R.mipmap.banner_four, R.mipmap.banner_five}; beans.add(new BannerBean(resIds)); beans.add(new SearchBean()); beans.add(new DividerBean()); beans.add(new ContentBean("one")); beans.add(new ContentBean("one")); beans.add(new ContentBean("one")); beans.add(new DividerBean()); beans.add(new ContentBean("two")); beans.add(new ContentBean("two")); beans.add(new ContentBean("two")); beans.add(new DividerBean()); beans.add(new ContentBean("three")); beans.add(new ContentBean("three")); beans.add(new ContentBean("three")); beans.add(new DividerBean()); beans.add(new ContentBean("four")); beans.add(new ContentBean("four")); beans.add(new ContentBean("four")); beans.add(new DividerBean()); MultiRecyclerAdapter multiRecyclerAdapter = new MultiRecyclerAdapter(beans); LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false); rvContent.setAdapter(multiRecyclerAdapter); rvContent.setLayoutManager(linearLayoutManager); }} 简单效果
写在最后
思路来源：
github上也有很多开源的万能Adapter，但是个人感觉这个思路虽然实现上代码会相对较多，但是层次分析，便于维护，扩展性较好。想要添加一个新类型的ItemType，只需要稍作修改即可快速完成，不用修改Adapter的代码。