(1)滚动事件分类
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
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
(2)监听RecyclerView的滚动
有两种方式可以监听滚动事件:
1.setOnScrollListener(OnScrollListener listener)
2.addOnScrollListener(OnScrollListener listener)
其中 setOnScrollListener 由于可能出现空指针的风险,已经过时。建议用addOnScrollListener。
(3)OnScrollListener
/**
* An OnScrollListener can be added to a RecyclerView to receive messages when a scrolling event
* has occurred on that RecyclerView.
* <p>
* @see RecyclerView#addOnScrollListener(OnScrollListener)
* @see RecyclerView#clearOnChildAttachStateChangeListeners()
*
*/
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){}
}
OnScrollListener类是个抽象类,有两个方法:
void onScrollStateChanged(RecyclerView recyclerView, int newState): 滚动状态变化时回调
void onScrolled(RecyclerView recyclerView, int dx, int dy): 滚动时回调
3.1 onScrollStateChanged(RecyclerView recyclerView, int newState)方法
回调的两个变量的含义:
recyclerView: 当前在滚动的RecyclerView
newState: 当前滚动状态.
其中newState有三种值:
/**
* The RecyclerView is not currently scrolling.(静止没有滚动)
*/
public static final int SCROLL_STATE_IDLE = 0;
/**
* The RecyclerView is currently being dragged by outside input such as user touch input.
*(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;
/**
* The RecyclerView is currently animating to a final position while not under outside control.
*(自动滚动)
*/
public static final int SCROLL_STATE_SETTLING = 2;
3.2 onScrolled(RecyclerView recyclerView, int dx, int dy)方法
回调的三个变量含义:
recyclerView : 当前滚动的view
dx : 水平滚动距离
dy : 垂直滚动距离
dx > 0 时为手指向左滚动,列表滚动显示右面的内容
dx < 0 时为手指向右滚动,列表滚动显示左面的内容
dy > 0 时为手指向上滚动,列表滚动显示下面的内容
dy < 0 时为手指向下滚动,列表滚动显示上面的内容
(4)canScrollVertically和canScrollHorizontally方法
public boolean canScrollVertically (int direction)
这个方法是判断View在竖直方向是否还能向上,向下滑动。
其中,direction为 -1 表示手指向下滑动(屏幕向上滑动), 1 表示手指向上滑动(屏幕向下滑动)。
public boolean canScrollHorizontally (int direction)
这个方法用来判断 水平方向的滑动
例如:
RecyclerView.canScrollVertically(1)的值表示是否能向下滚动,false表示已经滚动到底部
RecyclerView.canScrollVertically(-1)的值表示是否能向上滚动,false表示已经滚动到顶部
(5)两种判断是否到底部的方法:
5.1方法一:
如果 当前
第一个可见item的位置 + 当前可见的item个数 >= item的总个数
这样就可以判断出来,是在底部了。
loadingMoreListener = 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);
if (dy > 0) //向下滚动
{
int visibleItemCount = mLinearLayoutManager.getChildCount();
int totalItemCount = mLinearLayoutManager.getItemCount();
int pastVisiblesItems = mLinearLayoutManager.findFirstVisibleItemPosition();
if (!loading && (visibleItemCount + pastVisiblesItems) >= totalItemCount) {
loading = true;
loadMoreDate();
}
}
}
};
通过visibleItemCount + pastVisiblesItems) >= totalItemCount
来判断是否是底部。
5.2方法二:
通过canScrollVertically 来判断
loadingMoreListener = new RecyclerView.OnScrollListener() {
@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
if(!loading && !recyclerView.canScrollVertically(1)){
loading = true;
loadMoreDate();
}
}
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
// if (dy > 0) //向下滚动
// {
// int visibleItemCount = mLinearLayoutManager.getChildCount();
// int totalItemCount = mLinearLayoutManager.getItemCount();
// int pastVisiblesItems = mLinearLayoutManager.findFirstVisibleItemPosition();
//
// if (!loading && (visibleItemCount + pastVisiblesItems) >= totalItemCount) {
// loading = true;
// loadMoreDate();
// }
// }
}
};
参考:
http://blog.devwiki.net/index.php/2016/06/13/RecyclerView-Scroll-Listener.html
原文地址:https://www.cnblogs.com/xgjblog/p/8135660.html