Android RecycleView多布局实现

在做项目的过程中，我们会经常用到RecycleView来实现各种列表，但有时候我们也会遇到多布局的列表，今天我们来讲解一下RecycleView的多布局的实现方式及思路。
效果图奉上

效果图.gif

1、 单布局的Adapter

首先看下以前的单一布局是如何实现的：

我们继承RecycleView.Adapter，泛型是MyAdapter 中继承的ViewHolder类，这样写后我们的onCreateViewHolder和onBindViewHolder的方法参数都是我们的ViewHolder了，没有办法实现多布局的区分

  public class MoreLayoutAdapter  extends  RecyclerView.Adapter<MoreLayoutAdapter.ViewHolder> {
      @NonNull
      @Override
     public MoreLayoutAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
    return null;
        }

    @Override
    public void onBindViewHolder(@NonNull MoreLayoutAdapter.ViewHolder viewHolder, int i) {

      }

     @Override
    public int getItemCount() {
        return 0;
    }

    public class ViewHolder extends RecyclerView.ViewHolder{
    public ViewHolder(@NonNull View itemView) {
        super(itemView);
    }
 }

二、 多布局的Adapter

多布局的Adapter我们泛型为RecyclerView.ViewHolder，通过ViewType，我们区分使用不同的ViewHolder。

我们首先定义四个标志

//定义四种常量  表示四种条目类型
public static final int TYPE_TITLE = 1;
public static final int TYPE_TOP = 2;
public static final int TYPE_CENTER = 3;
public static final int TYPE_BOTTOM = 4;

RecyclerView提供了方法去区分ViewType,布局的类型要从Activity的传入到适配器里，用于和ViewType做匹配。

    @Override
   public int getItemViewType(int position) {
    SearchSecondHouseBean.DataBean.ErshoufangBean ershoufangBean = mErshoufangBeanList.get(position);
    if (ershoufangBean.getDatatype() == 1) {
        return TYPE_TITLE;
    } else if (ershoufangBean.getDatatype() == 2) {
        return TYPE_TOP;
    } else if (ershoufangBean.getDatatype() == 3) {
        return TYPE_CENTER;
    } else {
        return TYPE_BOTTOM;
    }
}

onCreateViewHolder的第二个参数int viewType就是getItemViewType的返回值

 public class MoreLayoutAdapter  extends RecyclerView.Adapter<MoreLayoutAdapter.ViewHolder>{
    @NonNull
    @Override
   public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int viewType) {
    View inflate;
    RecyclerView.ViewHolder holder = null;
    if (viewType == TYPE_TITLE) {
        inflate = LayoutInflater.from(mContext).inflate(R.layout.item_agent_card, viewGroup, false);
        return new TitleViewHolder(inflate);
    } else if (viewType == TYPE_TOP) {
        inflate = LayoutInflater.from(mContext).inflate(R.layout.item_second_good_house, viewGroup, false);
        return new ViewHolder(inflate);
    } else if (viewType == TYPE_CENTER) {
        inflate = LayoutInflater.from(mContext).inflate(R.layout.item_search_house_tuijian, viewGroup, false);
        return new CenterViewHolder(inflate);
    } else {
        inflate = LayoutInflater.from(mContext).inflate(R.layout.item_second_good_house, viewGroup, false);
        return new BottomViewHolder(inflate);
    }

}

在onBindViewHolder中，我们的来绑定数据

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position){
    if (viewHolder instanceof TitleViewHolder) {
            SearchSecondHouseBean.DataBean.ErshoufangBean bean =   mErshoufangBeanList.get(i);
            Glide.with(mContext).load(bean.getFengmian()).apply(new   RequestOptions().placeholder(R.drawable.default_bd).transform(new GlideRoundTransform(mContext))).into(((TitleViewHolder) viewHolder).mCivAgentCardIcon);
            ((TitleViewHolder) viewHolder).mTvAgentCardHouseName.setText(bean.getXiaoqu());
       }else if (viewHolder instanceof CenterViewHolder) {
            SearchSecondHouseBean.DataBean.ErshoufangBean   ershoufangBean = mErshoufangBeanList.get(i);
            ((CenterViewHolder) viewHolder).mTvTuiJianText.setText(ershoufangBean.getFangxing());
        } else if (viewHolder instanceof BottomViewHolder) {
            SearchSecondHouseBean.DataBean.ErshoufangBean bean = mErshoufangBeanList.get(i);
            Glide.with(mContext).load(bean.getFengmian()).apply(new RequestOptions().placeholder(R.drawable.default_bd).transform(new GlideRoundTransform(mContext))).into(((BottomViewHolder) viewHolder).mIvSecondGoodHouseIcon);
    }

ViewHolder的创建

public class CenterViewHolder extends RecyclerView.ViewHolder {
    TextView mTvTuiJianText;
    public CenterViewHolder(@NonNull View itemView) {
        super(itemView);
        mTvTuiJianText = itemView.findViewById(R.id.tv_tuijian_text);
    }
}

到这里基本就搞定了。

通过RecyclerView.Adapter设置多布局是非常方便的，而且大家可以发现当RecyclerView为LinearLayoutManager，我们可以通过viewType给RecyclerView来设置Header和Footer，如

public static final int HEADER = 1;
    public static final int FOOTER = 2;
    public static final int ITEM = 3;
    @Override
    public int getItemViewType(int position) {
        if(position == 0){
            return HEADER;
        }else if(position == getItemCount() -1){
            return FOOTER;
        }else{
            return ITEM;
        }
    }

    @Override
    public int getItemCount() {
        return mDatas.size() + 2;//Header和Footer
    }

但是当布局管理器为GridLayoutManager和StaggeredGridLayoutManager时就要不能这样去做了。

补充知识点：
了解一下子adapter的加载顺序

1. getItemViewType(int position)
   2.onCreateViewHolder(@NonNull ViewGroup viewGroup, int i)
   3.onBindViewHolder(@NonNull RecyclerView.ViewHolder viewHolder, final int i)
   其中第二步会把item的布局加载进来 与viewholder关联
   第三步会把数据与viewhoder关联