AndroidRecyclerView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:

1. 手指按下 -> 手指拖拽列表移动 -> 手指停止拖拽 -> 抬起手指

2. 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:

1. 静止 -> 被迫拖拽移动 -> 静止

2. 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.
*

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.

也就是说有两种方式可以监听滚动事件:

1. 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.
*

   
* 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

1. 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() {
@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
Log.i(TAG, "-----------onScrollStateChanged-----------");
Log.i(TAG, "newState: " + newState);
}
@Override
public 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:

   1. newState : 目前的状态

   2. dx : 水平滚动距离

   3. dy : 垂直滚动距离

   onScrollStateChanged 方法

   在

2. recyclerView : 当前在滚动的RecyclerView

3. 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() {
@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
}
@Override
public 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。