<Android 基础（三十五）> RecyclerView多类型Item的正确实现姿势

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：

RecyclerView基础使用

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

1. 便于维护。增删Item的类型不需要修改Adapter的代码；
2. 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
3. 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

1. 所有Bean类实现统一Visitable接口，实现type方法，返回对应的layout id;
2. 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。
3. 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。
4. 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 BaseViewHolder<T> extends RecyclerView.ViewHolder{
    SparseArray<View> 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);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="200dp">

    <cn.bingoogolapple.bgabanner.BGABanner
        android:id="@+id/bgabanner_header"
        android:layout_width="match_parent"
        android:layout_height="200dp">
    </cn.bingoogolapple.bgabanner.BGABanner>

</LinearLayout>

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);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <TextView
        android:id="@+id/tv_content"
        android:textStyle="italic"
        android:fontFamily="sans-serif-condensed"
        android:textSize="16sp"
        android:gravity="center_horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

DividerBean

public class DividerBean implements Visitable{

    @Override
    public int type(TypeFactory typeFactory) {
        return typeFactory.type(this);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@drawable/divider">

</LinearLayout>

SearchBean

public class SearchBean implements Visitable {
    @Override
    public int type(TypeFactory typeFactory) {
        return typeFactory.type(this);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" android:layout_width="match_parent"
    android:layout_height="50dp"
    android:padding="6dp">

    <EditText
        android:layout_marginLeft="30dp"
        android:id="@+id/et_search"
        android:layout_width="0dp"
        android:layout_weight="9"
        android:maxLines="1"
        android:textSize="10sp"
        android:paddingLeft="10dp"
        android:paddingRight="10dp"
        android:hint="输入文字搜索..."
        android:background="@drawable/bg_search"
        android:layout_height="match_parent" />

    <ImageView
        android:id="@+id/bt_search"
        android:layout_width="0dp"
        android:layout_weight="2"
        android:src="@drawable/search"
        android:layout_height="match_parent" />
</LinearLayout>

MultiRecyclerAdapter

public class MultiRecyclerAdapter extends RecyclerView.Adapter<BaseViewHolder> {
    List<Visitable> mData;
    TypeFactory typeFactory;

    public MultiRecyclerAdapter(List<Visitable> 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<Visitable> 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：

https://medium.com/@dpreussler/writing-better-adapters-1b09758407d2

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。