RecyclerView上拉加载更多

为什么要写这个呢，因为RecyclerView的上拉加载不像ListView通过添加FooterView那么方便，很多通过addScrollListener的方式实现的太繁琐，需要添加各种标识，需要交互联动。

不想说废话了，最好的不是好的，适合的才是最好的，代码如下：

public abstract class MyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
    private List<Object> items;
    protected Context context;
    private boolean isLoading;//是否正在加载
    private boolean hasLoadMore;//是否有加载更多，判断依据是如果增加的条目小于 aPageCount，那么就没有了
    private int aPageCount = 10;//每一页多少个，默认10，可根据后台返回的实际情况调节
    private OnLoadMoreListener loadMoreListener;
    private int currPage = 1;//当前加载的页标
    private final int TYPE_ITEM = 0, TYPE_FOOTER = 1;

    public MyAdapter(List<? extends Object> items, Context context) {
        if (items != null) {
            this.items = new ArrayList<>();
            this.items.addAll(items);
        }
        this.context = context;
    }

    public MyAdapter(List<? extends Object> items, Context context, int aPageCount) {
        if (items != null) {
            this.items = new ArrayList<>();
            this.items.addAll(items);
        }
        this.context = context;
        this.aPageCount = aPageCount;
    }

    public void setLoadMoreListener(OnLoadMoreListener loadMoreListener) {
        this.loadMoreListener = loadMoreListener;
    }

    public void notifyDataSetAndRefresh(List<? extends Object> data) {
        if (items == null) {
            items = new ArrayList<>();
        } else {
            items.clear();
        }
        currPage = 1;
        hasLoadMore = false;
        if (data != null) {
            if (data.size() >= aPageCount) {
                hasLoadMore = true;
            }
            items.addAll(data);
        }
        super.notifyDataSetChanged();
        isLoading = false;
    }


    public void notifyDataSetAndAdd(List<? extends Object> data) {
        if (items == null) items = new ArrayList<>();
        hasLoadMore = false;
        if (data != null) {
            if (data.size() >= aPageCount) {
                hasLoadMore = true;
            }
            items.addAll(data);
            if (loadMoreListener == null) {
                super.notifyItemRangeInserted(items.size() - data.size(), data.size());
            } else {
                super.notifyItemRangeChanged(items.size() - data.size(), data.size() + 1);
            }
            isLoading = false;
        }
    }

    public abstract void onBindItemData(RecyclerView.ViewHolder holder, Object itemBean);

    public abstract RecyclerView.ViewHolder getItemViewHolder(ViewGroup parent, int viewType);

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        if (viewType == TYPE_FOOTER) {
            return new MyFooterViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_loadmore, parent, false));
        }
        return getItemViewHolder(parent, viewType);
    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
        int itemViewType = getItemViewType(position);
        if (itemViewType == TYPE_FOOTER) {
            MyFooterViewHolder footerViewHolder = (MyFooterViewHolder) holder;
            footerViewHolder.refreshFooter(hasLoadMore);
            if (!isLoading && hasLoadMore) {
                isLoading = true;
                loadMoreListener.onLoadMore(++currPage);
            }
        } else {
            onBindItemData(holder, items.get(position));
        }
    }

    @Override
    public int getItemCount() {
        if (items == null) return 0;
        return loadMoreListener == null ? items.size() : items.size() + 1;
    }

    @Override
    public int getItemViewType(int position) {
        if (loadMoreListener != null && position == getItemCount() - 1) return TYPE_FOOTER;
        return TYPE_ITEM;
    }

    class MyFooterViewHolder extends RecyclerView.ViewHolder {
        LinearLayoutCompat llLoading;
        AppCompatTextView tvEnd;

        public MyFooterViewHolder(@NonNull View itemView) {
            super(itemView);
            llLoading = itemView.findViewById(R.id.ll_loading);
            tvEnd = itemView.findViewById(R.id.tv_end);
        }

        public void refreshFooter(boolean hasLoadMore) {
            if (hasLoadMore) {
                if (llLoading.getVisibility() == View.GONE) {
                    llLoading.setVisibility(View.VISIBLE);
                }
                if (tvEnd.getVisibility() == View.VISIBLE) {
                    tvEnd.setVisibility(View.GONE);
                }
            } else {
                if (tvEnd.getVisibility() == View.GONE) {
                    tvEnd.setVisibility(View.VISIBLE);
                }
                if (llLoading.getVisibility() == View.VISIBLE) {
                    llLoading.setVisibility(View.GONE);
                }
            }
        }
    }

    public interface OnLoadMoreListener {
        void onLoadMore(int page);
    }
}

item_loadmore.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:padding="5dp"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <androidx.appcompat.widget.AppCompatTextView
        android:id="@+id/tv_end"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="没有更多了..."
        android:textColor="@android:color/darker_gray" />

    <androidx.appcompat.widget.LinearLayoutCompat
        android:id="@+id/ll_loading"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:orientation="horizontal">

        <ProgressBar
            android:layout_width="30dp"
            android:layout_height="30dp" />

        <androidx.appcompat.widget.AppCompatTextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="5dp"
            android:text="加载中..."
            android:textColor="@android:color/darker_gray" />
    </androidx.appcompat.widget.LinearLayoutCompat>


</androidx.constraintlayout.widget.ConstraintLayout>

可以看到有两个抽象方法，具体的适配器新建一个类继承他，然后具体的ViewHolder和数据填充在那里面进行,比如：

public class MySearchListAdapter extends MyAdapter {


    public MySearchListAdapter(List<?> items, Context context) {
        super(items, context);
    }

    public MySearchListAdapter(List<?> items, Context context, int aPageCount) {
        super(items, context, aPageCount);
    }

	//带有我自己view的ViewHolder返回回去
    @Override
    public RecyclerView.ViewHolder getItemViewHolder(ViewGroup parent, int viewType) {
        return new MVViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_mv, null));
    }

	//具体的自己的数据绑定
    @Override
    public void onBindItemData(RecyclerView.ViewHolder holder, Object movieB) {
        MVViewHolder mvViewHolder = (MVViewHolder) holder;
        MBean mBean = (MBean) movieB;
        mvViewHolder.title.setText(mBean.title);
        mvViewHolder.leader.setText(mBean.leader);
        mvViewHolder.actor.setText(mBean.actor);
        mvViewHolder.country.setText(mBean.country);
        mvViewHolder.desc_simple.setText(mBean.desc_simple);
        Glide.with(context).load(mBean.imgUrl).into(mvViewHolder.iv);
        mvViewHolder.itemData = mBean;
    }

	//MBean是你自己的modal
    class MVViewHolder extends RecyclerView.ViewHolder {
        TextView title, leader, actor, country, desc_simple;
        ImageView iv;
        ConstraintLayout cl;
        MBean itemData;

        public MVViewHolder(@NonNull View itemView) {
            super(itemView);
            title = itemView.findViewById(R.id.title);
            leader = itemView.findViewById(R.id.leader);
            actor = itemView.findViewById(R.id.actor);
            country = itemView.findViewById(R.id.country);
            desc_simple = itemView.findViewById(R.id.desc_simple);
            iv = itemView.findViewById(R.id.iv);
            cl = itemView.findViewById(R.id.cl);
            cl.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {

                }
            });
        }
    }
}