Android RecyclerView 监听滑动

今天，简单讲讲Android 如何监听滑动。

不废话了，主要是需要做一个功能，实现RecyclerView滑动时，让一个标题栏固定显示在顶部。

基本知识：

列表的滚动一般分为两种:

手指按下 -> 手指拖拽列表移动 -> 手指停止拖拽 -> 抬起手指
手指按下 -> 手指快速拖拽后抬起手指 -> 列表继续滚动 -> 停止滚动

从上面可以看出,滚动状态分为:

|--静止
|--滚动|--被迫拖拽移动|--自己滚动

上面的过程的状态变化如下:

静止 -> 被迫拖拽移动 -> 静止
静止 -> 被迫拖拽移动 -> 自己滚动 -> 静止

监听RecyclerView的滚动

好了,我们分析完滚动的过程,再看看如何监听RecyclerView的滚动.查看源码是最好的方法.

看源码

查看RecyclerView的源码,我们可以看到以下代码:

/*** Set a listener that will be notified of any changes in scroll state or position.* @param listener Listener to set or null to clear* @deprecated Use {@link #addOnScrollListener(OnScrollListener)} and*             {@link #removeOnScrollListener(OnScrollListener)}*/
@Deprecated
public void setOnScrollListener(OnScrollListener listener) {mScrollListener = listener;
}/*** Add a listener that will be notified of any changes in scroll state or position.* <p>Components that add a listener should take care to remove it when finished.* Other components that take ownership of a view may call {@link #clearOnScrollListeners()}* to remove all attached listeners.</p>* @param listener listener to set or null to clear*/
public void addOnScrollListener(OnScrollListener listener) {if (mScrollListeners == null) {mScrollListeners = new ArrayList<>();}mScrollListeners.add(listener);
}

也就是说有两种方式可以监听滚动事件:

其中 setOnScrollListener 已经过时( 设置的监听器源码如下:

public abstract static class OnScrollListener {/*** Callback method to be invoked when RecyclerView's scroll state changes.* @param recyclerView The RecyclerView whose scroll state has changed.* @param newState     The updated scroll state. One of {@link #SCROLL_STATE_IDLE},*                     {@link #SCROLL_STATE_DRAGGING} or {@link #SCROLL_STATE_SETTLING}.*/public void onScrollStateChanged(RecyclerView recyclerView, int newState){}/*** Callback method to be invoked when the RecyclerView has been scrolled. This will be* called after the scroll has completed.* <p>* This callback will also be called if visible item range changes after a layout* calculation. In that case, dx and dy will be 0.** @param recyclerView The RecyclerView which scrolled.* @param dx The amount of horizontal scroll.* @param dy The amount of vertical scroll.*/public void onScrolled(RecyclerView recyclerView, int dx, int dy){}
}

在滚动过程中,此监听器会回调两个方法.

onScrollStateChanged : 滚动状态变化时回调
onScrolled : 滚动时回调

这两者的区别在于: 状态与过程

举例子

注 : 以下源码可在最后的地址中找到.

demoRv = (RecyclerView) findViewById(R.id.demo_rv);
layoutManager = new LinearLayoutManager(this);
demoRv.setLayoutManager(layoutManager);
demoRv.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL_LIST));bookAdapter = new BookAdapter();
bookAdapter.fillList(MockService.getBookList());
demoRv.setAdapter(bookAdapter);demoRv.addOnScrollListener(new RecyclerView.OnScrollListener() {@Overridepublic void onScrollStateChanged(RecyclerView recyclerView, int newState) {super.onScrollStateChanged(recyclerView, newState);Log.i(TAG, "-----------onScrollStateChanged-----------");Log.i(TAG, "newState: " + newState);}@Overridepublic void onScrolled(RecyclerView recyclerView, int dx, int dy) {super.onScrolled(recyclerView, dx, dy);Log.i(TAG, "-----------onScrolled-----------");Log.i(TAG, "dx: " + dx);Log.i(TAG, "dy: " + dy);Log.i(TAG, "CHECK_SCROLL_UP: " + recyclerView.canScrollVertically(TAG_CHECK_SCROLL_UP));Log.i(TAG, "CHECK_SCROLL_DOWN: " + recyclerView.canScrollVertically(TAG_CHECK_SCROLL_DOWN));}
});

以上代码中输出了主要个几个信息:

newState : 目前的状态
dx : 水平滚动距离
dy : 垂直滚动距离

onScrollStateChanged 方法

在

recyclerView : 当前在滚动的RecyclerView
newState : 当前滚动状态.

其中newState有三种值:

//停止滚动
public static final int SCROLL_STATE_IDLE = 0;//正在被外部拖拽,一般为用户正在用手指滚动
public static final int SCROLL_STATE_DRAGGING = 1;//自动滚动开始
public static final int SCROLL_STATE_SETTLING = 2;

onScrolled 方法

在

recyclerView : 当前滚动的view
dx : 水平滚动距离
dy : 垂直滚动距离

真机实践

运行代码

运行以上代码,然后按照上面的滚动过程分别进行两种滚动.

第一种方式缓慢滚动结果如下:

I/MainActivity: -----------onScrollStateChanged-----------
I/MainActivity: newState: 1
I/MainActivity: -----------onScrolled-----------
I/MainActivity: dx: 0
I/MainActivity: dy: -6
I/MainActivity: CHECK_SCROLL_UP: true
I/MainActivity: CHECK_SCROLL_DOWN: true
------------------------n个onScrolled--------------------
I/MainActivity: -----------onScrolled-----------
I/MainActivity: dx: 0
I/MainActivity: dy: -2
I/MainActivity: CHECK_SCROLL_UP: true
I/MainActivity: CHECK_SCROLL_DOWN: false
I/MainActivity: -----------onScrollStateChanged-----------
I/MainActivity: newState: 0

第二种快速滚动结果如下:

I/MainActivity: -----------onScrollStateChanged-----------
I/MainActivity: newState: 1
I/MainActivity: -----------onScrolled-----------
I/MainActivity: dx: 0
I/MainActivity: dy: 59
I/MainActivity: CHECK_SCROLL_UP: true
I/MainActivity: CHECK_SCROLL_DOWN: true
--------------------------n个onScrolled-------------------
I/MainActivity: -----------onScrolled-----------
I/MainActivity: dx: 0
I/MainActivity: dy: 54
I/MainActivity: CHECK_SCROLL_UP: true
I/MainActivity: CHECK_SCROLL_DOWN: true
I/MainActivity: -----------onScrollStateChanged-----------
I/MainActivity: newState: 2
I/MainActivity: -----------onScrolled-----------
I/MainActivity: dx: 0
I/MainActivity: dy: 56
I/MainActivity: CHECK_SCROLL_UP: true
I/MainActivity: CHECK_SCROLL_DOWN: true
--------------------------n个onScrolled-------------------
I/MainActivity: -----------onScrolled-----------
I/MainActivity: dx: 0
I/MainActivity: dy: 14
I/MainActivity: CHECK_SCROLL_UP: true
I/MainActivity: CHECK_SCROLL_DOWN: true
I/MainActivity: -----------onScrolled-----------
I/MainActivity: dx: 0
I/MainActivity: dy: 1
I/MainActivity: CHECK_SCROLL_UP: true
I/MainActivity: CHECK_SCROLL_DOWN: true
I/MainActivity: -----------onScrollStateChanged-----------
I/MainActivity: newState: 0

分析结果

且在滚动过程中发现:

1.滚动方向

dy > 0 时为向上滚动
dy < 0 时为向下滚动

2.回调过程

缓慢拖拽回调过程:

1. newState = RecyclerView.SCROLL_STATE_DRAGGING;
2. dy 多次改变
3. newState = RecyclerView.SCROLL_STATE_IDLE

快速滚动回调过程:

1. newState = RecyclerView.SCROLL_STATE_DRAGGING;
2. dy 多次改变
3. newState = RecyclerView.SCROLL_STATE_SETTLING;
4. dy 多次改变
5. newState = RecyclerView.SCROLL_STATE_IDLE;

3.顶端与底部

以上信息中还打印了

RecyclerView.canScrollVertically(-1)的值表示是否滚动到顶部

这些是基本知识，参考文章：https://www.cnblogs.com/ldq2016/p/6645952.html

具体实现：

在界面上设置一个标题栏，在RecyclerView 中的一个item和标题栏一致，当RecyclerView滑动到标题栏时，显示界面上的标题栏，小于位置时，隐藏界面上的标题栏。我这个RecyclerView 的标题栏是第2个item。

 mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {@Overridepublic void onScrollStateChanged(RecyclerView recyclerView, int newState) {super.onScrollStateChanged(recyclerView, newState);}@Overridepublic void onScrolled(RecyclerView recyclerView, int dx, int dy) {super.onScrolled(recyclerView, dx, dy);int firstItemPosition = linearLayoutManager.findFirstVisibleItemPosition();Log.e("TAG", " PersonalHomepageActivity " + firstItemPosition);if (firstItemPosition >= 1 && llBookTitle.getVisibility() == View.GONE) {llBookTitle.setVisibility(View.VISIBLE);} else if (firstItemPosition == 0 && llBookTitle.getVisibility() == View.VISIBLE) {llBookTitle.setVisibility(View.GONE);}}});

Android RecyclerView 监听滑动就讲完了。

就这么简单。