我有这段代码:
mRecycleView.setOnScrollListener(new RecyclerView.OnScrollListener() {
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
int[] firstVisibleItemPositions = new int[getResources().getInteger(R.integer.news_numbers_column)];
int pastVisiblesItems = ((StaggeredGridLayoutManager)getLayoutManager()).findFirstVisibleItemPositions(firstVisibleItemPositions)[0];
}
});
当我滚动我的recycleview时,我收到此错误:
java.lang.NullPointerException: Attempt to invoke virtual method 'int android.support.v7.widget.OrientationHelper.getStartAfterPadding()' on a null object reference
at android.support.v7.widget.StaggeredGridLayoutManager$Span.findOneVisibleChild(StaggeredGridLayoutManager.java:2177)
at android.support.v7.widget.StaggeredGridLayoutManager$Span.findFirstVisibleItemPosition(StaggeredGridLayoutManager.java:2153)
at android.support.v7.widget.StaggeredGridLayoutManager.findFirstVisibleItemPositions(StaggeredGridLayoutManager.java:806)
at info.lanouvelletribune.apps.android.ui.fragments.NewsFragment$1.onScrollStateChanged(NewsFragment.java:90)
at android.support.v7.widget.RecyclerView.setScrollState(RecyclerView.java:751)
at android.support.v7.widget.RecyclerView.onInterceptTouchEvent(RecyclerView.java:1535)
at com.github.ksoichiro.android.observablescrollview.ObservableRecyclerView.onInterceptTouchEvent(ObservableRecyclerView.java:188)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2060)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2431)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2173)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2431)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2173)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2431)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2173)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2431)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2173)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2431)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2173)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2431)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2173)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2431)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2173)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2431)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2173)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2431)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2173)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2431)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2173)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2431)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2173)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2431)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2173)
at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2390)
at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1741)
at android.app.Activity.dispatchTouchEvent(Activity.java:2826)
at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2351)
at android.view.View.dispatchPointerEvent(View.java:8590)
at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4098)
at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3964)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3488)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3541)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3507)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3515)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3488)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3541)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3507)
at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3617)
at android
如何处理此错误并获取第一个可见项目位置?
答案 0 :(得分:23)
我用这段代码对它进行了测试,它可以和我一起使用
int positionView = ((LinearLayoutManager)recyclerView.getLayoutManager()).findFirstVisibleItemPosition();
我使用了循环视图参数。
答案 1 :(得分:6)
试试这个:
int position = layoutManager.findFirstVisibleItemPositions(null)[0];
其中layoutManager
是您在recyclerview
中设置的内容。
例如,
layoutManager = new StaggeredGridLayoutManager(2,StaggeredGridLayoutManager.VERTICAL);
mrecyclerView.setLayoutManager(layoutManager );
答案 2 :(得分:1)
您可以使用:
int[] firstVisibleItemPositions = new int[yourNumberOfColumns];
int pastVisiblesItems = layoutManager.findFirstVisibleItemPositions(firstVisibleItemPositions)[0];
答案 3 :(得分:0)
这是RecyclerView StaggeredGridLayoutManager中的一个错误:
https://code.google.com/p/android/issues/detail?id=180521
https://code.google.com/p/android/issues/detail?id=181461
解决方法是尝试/捕获异常:
try {
((StaggeredGridLayoutManager)getLayoutManager()).findFirstVisibleItemPositions(firstVisibleItemPositions);
} catch (NullPointerException ex) {
// workaround for RecyclerView bug. assume not laid out, so no items visible
firstVisibleItemPositions[0] = RecyclerView.NO_POSITION;
firstVisibleItemPositions[1] = RecyclerView.NO_POSITION;
}
答案 4 :(得分:0)
如果您使用的是StaggeredGridLayoutManager,您可以找到 findLastVisibleItemPositions ,如下所示:
int visibleThreshold =1;
final StaggeredGridLayoutManager linearLayoutManager = (StaggeredGridLayoutManager) mRecyclerViewAllPost.getLayoutManager();
mRecyclerViewAllPost.addOnScrollListener(new RecyclerView.OnScrollListener() {
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
int[] lastVisibleItemPositions = linearLayoutManager.findLastVisibleItemPositions(null);
int lastVisibleItem = getLastVisibleItem(lastVisibleItemPositions);
int totalItemCount = linearLayoutManager.getItemCount();
if (!isLoading && totalItemCount <= (lastVisibleItem + visibleThreshold)) {
print("load more item ");
isLoading = true;
}
}
});
和 getLastVisibleItem 方法如下:
public int getLastVisibleItem(int[] lastVisibleItemPositions) {
int maxSize = 0;
for (int i = 0; i < lastVisibleItemPositions.length; i++) {
if (i == 0) {
maxSize = lastVisibleItemPositions[i];
}
else if (lastVisibleItemPositions[i] > maxSize) {
maxSize = lastVisibleItemPositions[i];
}
}
return maxSize;
}
答案 5 :(得分:0)
您可以这样尝试:
StaggeredGridLayoutManager staggeredGridLayoutManager = (StaggeredGridLayoutManager) recyclerView.getLayoutManager();
或者您可以直接使用staggeredlayoutManager
对象代替上面的对象:
int[] into = staggeredGridLayoutManager .findLastVisibleItemPositions(null);
List<Integer> intoList = new ArrayList<>();
for (int i : into)
{
intoList.add(i);
}
int firstVisbleoitem= Collections.max(intoList);
答案 6 :(得分:0)
使用这两种方法:
/**
* @return Last visible item position for staggeredGridLayoutManager
*/
private int getLastVisibleItem(int[] lastVisibleItemPositions) {
int maxSize = 0;
for (int position : lastVisibleItemPositions) {
if (position > maxSize) {
maxSize = position;
}
}
return maxSize;
}
/**
* @return First visible item position for staggeredGridLayoutManager
*/
private int getFirstVisibleItem(int[] firstVisibleItemPositions) {
int minSize = 0;
if (firstVisibleItemPositions.length > 0) {
minSize = firstVisibleItemPositions[0];
for (int position : firstVisibleItemPositions) {
if (position < minSize) {
minSize = position;
}
}
}
return minSize;
}
和getLastVisibleItem方法如下:
int[] lastVisibleItemPositions = ((StaggeredGridLayoutManager) layoutManager).findLastVisibleItemPositions(null);
int[] firstVisibleItemPositions = ((StaggeredGridLayoutManager) layoutManager).findFirstVisibleItemPositions(null);
// get maximum element within the list
lastVisibleItem = getLastVisibleItem(lastVisibleItemPositions);
firstVisibleItem = getFirstVisibleItem(firstVisibleItemPositions);