因為今天還有點工作上的事沒做完，所以就不吹B了，介紹完庫寫完解釋就吃飯去了，下午還要幹活呢

InfiniteScroll

在傳統的ListView李有PullToFressh做下拉重新整理之類的實現，今天上一個類似的效果InfiniteScroll，不過他是寄存在RecycleView下的更符合發展趨勢

效果圖：

拉到底就加在更多出現Dialog的效果，使用場景很多

how to use?

Grade:

dependencies {
  compile 'com.github.pwittchen:infinitescroll:0.0.1'
}

Maven:

<dependency
 
>
    <groupId>com.github.pwittchen</groupId>
    <artifactId>infinitescroll</artifactId>
    <version>0.0.1</version>
</dependency>

Eclipse:把圈圈那部分Copy了就行

再來說下具體怎麼引用，直接貼例子程式碼在裡面有詳細解釋

public class MainActivity extends AppCompatActivity {
    private static
 
 final int MAX_ITEMS_PER_REQUEST = 20;//每次請求item數
    private static final int NUMBER_OF_ITEMS = 100;//最大item數
    private static final int SIMULATED_LOADING_TIME_IN_MS = 1500;//模擬耗時操作睡執行緒的時間

    public Toolbar toolbar;
    public RecyclerView recyclerView;
    public ProgressBar progressBar;

    private MyAdapter myAdapter;
    private
 
 LinearLayoutManager layoutManager;
    private List<String> items;
    private int page = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //初始化資料來源
        this.items = createItems();
        //獲取控制元件id
        initViews();
        //初始化RecyclerView
        initRecyclerView();
        setSupportActionBar(toolbar);
    }
    //如果<10 那就前面+"0"
    private List<String> createItems() {
        List<String> items = new LinkedList<>();
        for (int i = 0; i < NUMBER_OF_ITEMS; i++) {
            String prefix = i < 10 ? "0" : "";
            items.add("Item #".concat(prefix).concat(String.valueOf(i)));
        }
        return items;
    }

    private void initViews() {
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
        progressBar = (ProgressBar) findViewById(R.id.progress_bar);
    }

    private void initRecyclerView() {
        layoutManager = new LinearLayoutManager(this);
        //如果item高度不變,提升效能操作
        recyclerView.setHasFixedSize(true);
        //設定ListView樣式
        recyclerView.setLayoutManager(layoutManager);
        //新增介面卡,subList方法截取了原本100長度的ArrayList的0->MAX_ITEMS_PER_REQUEST 部分
        myAdapter = new MyAdapter(items.subList(page, MAX_ITEMS_PER_REQUEST));
        recyclerView.setAdapter(myAdapter);
        //新增滑動監聽
        recyclerView.addOnScrollListener(createInfiniteScrollListener());

        myAdapter.setOnItemClickListener(new MyAdapter.OnRecyclerViewItemClickListener() {
            @Override
            public void onItemClick(View view, int position) {
                Toast.makeText(MainActivity.this, "第" + position + "被點選", Toast.LENGTH_SHORT).show();
            }
        });
    }

    @NonNull
    private InfiniteScrollListener createInfiniteScrollListener() {
        return new InfiniteScrollListener(MAX_ITEMS_PER_REQUEST, layoutManager) {
            //重新整理後第一個可見的item位置
            @Override
            public void onScrolledToEnd(final int firstVisibleItemPosition) {
                Log.d("-->firstVisible","firstVisibleItemPosition : "+firstVisibleItemPosition);
                simulateLoading();
                //每次載入X * 20個item
                int start = ++page * MAX_ITEMS_PER_REQUEST;
                final boolean allItemsLoaded = start >= items.size();
                if (allItemsLoaded) {
                    progressBar.setVisibility(View.GONE);
                } else {
                    int end = start + MAX_ITEMS_PER_REQUEST;
                    //合成新的資料來源
                    final List<String> items = getItemsToBeLoaded(start, end);
                    //重新重新整理View
                    refreshView(recyclerView, new MyAdapter(items), firstVisibleItemPosition);
                }
            }
        };
    }

    @NonNull
    private List<String> getItemsToBeLoaded(int start, int end) {
        List<String> newItems = items.subList(start, end);
        final List<String> oldItems = ((MyAdapter) recyclerView.getAdapter()).getItems();
        final List<String> items = new LinkedList<>();
        items.addAll(oldItems);
        items.addAll(newItems);
        return items;
    }

    /**
     * WARNING! This method is only for demo purposes!
     * Don't do anything like that in your regular project!
     */
    private void simulateLoading() {
        new AsyncTask<Void, Void, Void>() {
            @Override
            protected void onPreExecute() {
                progressBar.setVisibility(View.VISIBLE);
            }

            @Override
            protected Void doInBackground(Void... params) {
                try {
                    Thread.sleep(SIMULATED_LOADING_TIME_IN_MS);
                } catch (InterruptedException e) {
                    Log.e("MainActivity", e.getMessage());
                }
                return null;
            }

            @Override
            protected void onPostExecute(Void param) {
                progressBar.setVisibility(View.GONE);
            }
        }.execute();
    }
}

流程是這樣的，一開始做了一個假資料，然後拉到底就重新整理，然後拉到底就重新整理然後重新整理到最大值就不做增加的操作了，但是判斷還是一直有的

上圖是不重新整理但還在判斷的證據

那我們來大致看看這個下拉的判斷是如何實現的

//繼承於RecyclerView.OnScrollListener，也就有了一個很重要的方法
// onScrolled(RecyclerView recyclerView, int dx, int dy)
public abstract class InfiniteScrollListener extends RecyclerView.OnScrollListener

//建構函式分別傳入2個引數,一個是要被載入的最大值，還有個是LinearLayoutManager物件,然後再是做異常處理，為空什麼的
   public InfiniteScrollListener(int maxItemsPerRequest, LinearLayoutManager layoutManager) {
        Preconditions.checkIfPositive(maxItemsPerRequest, "maxItemsPerRequest <= 0");
        Preconditions.checkNotNull(layoutManager, "layoutManager == null");
        this.maxItemsPerRequest = maxItemsPerRequest;
        this.layoutManager = layoutManager;
    }

     //具體執行操作和回撥做事的地方,返回的也就是那個可見第一個item的position
     @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);
        //這邊就是判斷是否能加在
        if (canLoadMoreItems()) {
            onScrolledToEnd(layoutManager.findFirstVisibleItemPosition());
        }
    }

//載入完重新整理的操作，然後再移到那個標誌位的位置上去，這也就是為什麼每次我們重新整理完沒有跳到最上面的原因
protected void refreshView(RecyclerView view, RecyclerView.Adapter adapter, int position) {
        view.setAdapter(adapter);
        view.invalidate();
        view.scrollToPosition(position);
    }

  //抽象方法了，給我們實現用
  public abstract void onScrolledToEnd(final int firstVisibleItemPosition);

整體實現不太難，但是有很好的思路，所以給大家推薦下。