Paging分页库-无限滚动(添加Header和Footer)

导入依赖库：

    compile 'android.arch.paging:runtime:1.0.1'

使用Paging实现无限滚动，实现清空、更新、初始化功能，并且添加header和footer

public class PagingActivity extends AppCompatActivity {
    public class Student{
        public int id;
        public String name;
    }
    @BindView(R.id.recyclerViewId)
    RecyclerView mRecyclerView;
    MyAdpater adpater;
    PagedList.Config config;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_paging);
        ButterKnife.bind(this);
        adpater = new MyAdpater();
        config = new PagedList.Config.Builder()
                .setEnablePlaceholders(false)//配置是否启动PlaceHolders，这里设置是否设置PagedList中的占位符,如果设置为true,我们的数据数量必须固定,由于网络数据数量不固定,所以设置false
                .setInitialLoadSizeHint(20)//初始化加载的数量
                .setPageSize(10)//配置分页加载的数量
//                .setPrefetchDistance(2)     //距离底部还有多少条数据时开始预加载
                .build();
        LiveData> liveData = new LivePagedListBuilder(MyDataSourceFactory,config).build();
        liveData.observe(this, new Observer>() {
            @Override
            public void onChanged(@Nullable PagedList students) {
                adpater.submitList(students);
            }
        });
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        mRecyclerView.setAdapter(adpater);
    }

    @OnClick(R.id.clearBtn)
    public void onClearClicked(){
        adpater.submitList(null);//清空数据
    }

    @OnClick(R.id.initBtn)
    public void onInitClicked(){//初始化数据
        LiveData> liveData = new LivePagedListBuilder(MyDataSourceFactory,config).build();
        liveData.observe(this, new Observer>() {
            @Override
            public void onChanged(@Nullable PagedList students) {
                adpater.submitList(students);
            }
        });
    }

    @OnClick(R.id.updateBtn)
    public void onUpdateClicked(){//更新数据
        adpater.getCurrentList().get(8).name="修改了姓名";
        adpater.notifyItemChanged(8);
    }

    DataSource.Factory MyDataSourceFactory = new DataSource.Factory() {
        @Override
        public DataSource create() {
            return new MyDataSource();
        }
    };

    class MyDataSource extends PositionalDataSource{

        @Override
        public void loadInitial(@NonNull LoadInitialParams params, @NonNull LoadInitialCallback callback) {
            callback.onResult(loadData(0,20),0,100);//setEnablePlaceholders为false：忽略总计数（非必填），true:总共请求totalCount(必填)
        }

        @Override
        public void loadRange(@NonNull LoadRangeParams params, @NonNull LoadRangeCallback callback) {
//            if(params.startPosition<100) {
                callback.onResult(loadData(params.startPosition, 10));
//            }
        }
    }

    class MyDataSource2 extends PageKeyedDataSource{

        @Override
        public void loadInitial(@NonNull LoadInitialParams params, @NonNull LoadInitialCallback callback) {
            callback.onResult(loadData(0,20),0,100,0,10);
        }

        @Override
        public void loadBefore(@NonNull LoadParams params, @NonNull LoadCallback callback) {
//            callback.onResult(loadData(params.key,10),params.key-1);
        }

        @Override
        public void loadAfter(@NonNull final LoadParams params, @NonNull LoadCallback callback) {
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    Toast.makeText(getApplicationContext(),params.key/10+"",Toast.LENGTH_SHORT).show();
                }
            });

            callback.onResult(loadData(params.key,10),params.key+10);
        }
    }

    /**
     * 假设这里需要做一些后台线程的数据加载任务。
     *
     * @param startPosition
     * @param count
     * @return
     */
    private List loadData(int startPosition,int count) {
        List list = new ArrayList();

        for (int i = 0; i < count; i++) {
            Student data = new Student();
            data.id = startPosition + i;
            data.name = "姓名：abc" + data.id;
            list.add(data);
        }

        return list;
    }

    DiffUtil.ItemCallback diffCallback = new DiffUtil.ItemCallback() {
        @Override
        public boolean areItemsTheSame(Student oldItem, Student newItem) {
            return oldItem.id == newItem.id;
        }

        @Override
        public boolean areContentsTheSame(Student oldItem, Student newItem) {
            return oldItem.equals(newItem);
        }
    };
    class MyAdpater extends PagedListAdapter{

        public MyAdpater(){
            super(diffCallback);
        }

        @Override
        public int getItemViewType(int position) {
            int itemCount = getItemCount() - 1;
            if(position == 0){
                return ITEM_TYPE_HEADER;
            }else if(position == itemCount){
                return ITEM_TYPE_FOOTER;
            }else{
                return super.getItemViewType(position);
            }
        }

        @Override
        public int getItemCount() {
            return super.getItemCount() + 2;
        }

        @Nullable
        @Override
        protected Student getItem(int position) {
            return super.getItem(position-1);
        }

        @NonNull
        @Override
        public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            switch(viewType){
                case ITEM_TYPE_HEADER:
                    TextView headerTv = new TextView(getApplicationContext());
                    ViewGroup.LayoutParams params = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,150);
                    headerTv.setLayoutParams(params);
                    headerTv.setTextSize(28);
                    headerTv.setText("I am header");
                    headerTv.setTextColor(Color.WHITE);
                    headerTv.setBackgroundColor(Color.BLUE);
                    headerTv.setGravity(Gravity.CENTER);
                    return new HeaderViewHolder(headerTv);
                case ITEM_TYPE_FOOTER:
                    TextView footTv = new TextView(getApplicationContext());
                    footTv.setText("I am footer");
                    return new FooterViewHolder(footTv);
                default:
                    View view = LayoutInflater.from(getApplicationContext()).inflate(R.layout.list_item_layout,null);
                    return new MyViewHolder(view);
            }
        }

        @Override
        public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
            if(holder instanceof MyViewHolder) {
                ((MyViewHolder)holder).nameTv.setText(getItem(position).name);
                ((MyViewHolder)holder).idTv.setText(getItem(position).id + "");
            }
        }
        //添加header和footer,重写AdapterDataObserver
        @Override
        public void registerAdapterDataObserver(@NonNull RecyclerView.AdapterDataObserver observer) {
            super.registerAdapterDataObserver(new AdapterDataObserverProxy(observer,1));
        }

        private static final int ITEM_TYPE_HEADER = -99;
        private static final int ITEM_TYPE_FOOTER = -100;
    }
    class MyViewHolder extends RecyclerView.ViewHolder{
        public TextView nameTv,idTv;
        public MyViewHolder(View itemView) {
            super(itemView);
            nameTv = itemView.findViewById(R.id.nameTv);
            idTv = itemView.findViewById(R.id.idTv);
        }
    }

    class HeaderViewHolder extends RecyclerView.ViewHolder{
        public HeaderViewHolder(View itemView) {
            super(itemView);
        }
    }
    class FooterViewHolder extends RecyclerView.ViewHolder{
        public FooterViewHolder(View itemView) {
            super(itemView);
        }
    }
}

重写AdapterDataObserver

// 1.新建一个 AdapterDataObserverProxy 类继承 RecyclerView.AdapterDataObserver
class AdapterDataObserverProxy extends RecyclerView.AdapterDataObserver {
    RecyclerView.AdapterDataObserver adapterDataObserver;
    int headerCount;
    public AdapterDataObserverProxy(RecyclerView.AdapterDataObserver adapterDataObserver, int headerCount) {
        this.adapterDataObserver = adapterDataObserver;
        this.headerCount = headerCount;
    }
    @Override
    public void onChanged() {
        adapterDataObserver.onChanged();
    }
    @Override
    public void onItemRangeChanged(int positionStart, int itemCount) {
        adapterDataObserver.onItemRangeChanged(positionStart + headerCount, itemCount);
    }
    @Override
    public void onItemRangeChanged(int positionStart, int itemCount, @Nullable Object payload) {
        adapterDataObserver.onItemRangeChanged(positionStart + headerCount, itemCount, payload);
    }

    // 当第n个数据被获取，更新第n+1个position
    @Override
    public void onItemRangeInserted(int positionStart, int itemCount) {
        adapterDataObserver.onItemRangeInserted(positionStart + headerCount, itemCount);
    }
    @Override
    public void onItemRangeRemoved(int positionStart, int itemCount) {
        adapterDataObserver.onItemRangeRemoved(positionStart + headerCount, itemCount);
    }
    @Override
    public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
        super.onItemRangeMoved(fromPosition + headerCount, toPosition + headerCount, itemCount);
    }
}

参考：https://blog.csdn.net/mq2553299/article/details/89075709