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最近看战狼二，看的是激动不已，今天也趁热打铁总结下recyclerVeiw中一些常见的小知识点。
如果在开发中要嵌套scrollview怎么办？
其实在开发中嵌套scrollview网上有的说重写LayoutManager等等，效果不是很明显，你可以去搜搜。现在给出的解决方案是
NestedScrollView 包裹RecyclerView。妈妈再也不用担心嵌套滑动的问题。然后在代码中加上：
my_recyler.setNestedScrollingEnabled(false);
这就是解决嵌套recyclerVeiw的终极解决方法。
RecyclerView.OnScrollListener
（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
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){}
}
onScrollStateChanged
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
newState 状态码
/**
* 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;
状态发生改变的时候会调用。接下来针对两种滑动过程具体onScrollStateChanged 是怎么打印信息的
- 1.静止 -> 被迫拖拽移动 -> 静止
image.png
- 2.静止 -> 被迫拖拽移动 -> 自己滚动 -> 静止
image.png
onScrolled（）
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
具体的日志信息就不打印了。
不过这个方法值判断recyclerVeiw有么有滑动到底部的方法
判断滑动到底部的方法
方法一：第一个可见item的位置 + 当前可见的item个数 >= item的总个数
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();//该方法是得到当前可见的子视图的个数
int totalItemCount = mLinearLayoutManager.getItemCount();//返回的是当前所有的item的个数
int pastVisiblesItems = mLinearLayoutManager.findFirstVisibleItemPosition();//返回的是从顶部开始划出屏幕是个数，即已经可见的视图的个数
if (!loading && (visibleItemCount + pastVisiblesItems) >= totalItemCount) {
loading = true;
loadMoreDate();
}
}
}
};
image.png
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();
// }
// }
}
};
方法三：
RecyclerView.OnScrollListener listener = new RecyclerView.OnScrollListener() {
@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
Log.i("jimmy","onScrollStateChanged"+"滑动状态"+newState);
}
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
// Log.i("jimmy","onScrolled"+"滑动dx的值="+dx+"滑动dy的值"+dy);
if (dy > 0) //向下滚动
{
// int visibleItemCount = recyclerView.getLayoutManager().getChildCount();
int totalItemCount = recyclerView.getLayoutManager().getItemCount();
// int pastVisiblesItems = manager.findFirstVisibleItemPosition();
int lastvisibleitemcount = manager.findLastVisibleItemPosition();
// Log.i("jimmy","onScrolled==visibleItemCount的值=="+visibleItemCount+"totalItemCount的值为==="+totalItemCount+"pastVisiblesItems的值为==="+pastVisiblesItems);
Log.i("jimmy","onScrolled===lastvisibleitemcount的值=="+lastvisibleitemcount);
// if ((visibleItemCount + pastVisiblesItems) >= totalItemCount) {
// Log.i("jimmy","onScrolled滑动到底部了");
// }
if ((lastvisibleitemcount + 1) >= totalItemCount) {
Log.i("jimmy","onScrolled滑动到底部了");
}
}
}
};
image.png
最后还要说说adapter的封装问题，水平有限
推荐个学习链接：https://github.com/CymChad/BaseRecyclerViewAdapterHelper
