Java findFirstVisibleItemPositions不'；I don’’我不为回收站工作

我有以下代码：

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，出现以下错误：

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得第一个可见的项目位置？

我使用此代码对其进行了测试，并且效果良好

int positionView = ((LinearLayoutManager)recyclerView.getLayoutManager()).findFirstVisibleItemPosition();

我使用了recycle view参数。

尝试以下操作：

int position = layoutManager.findFirstVisibleItemPositions(null)[0];

其中

layoutManager

是您在

recyclerview

中设置的内容

比如说,

layoutManager = new StaggeredGridLayoutManager(2,StaggeredGridLayoutManager.VERTICAL);
mrecyclerView.setLayoutManager(layoutManager );

---

这是RecyclerView EdgridLayoutManager中的一个错误：

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;
}

您可以使用以下选项：

int[] firstVisibleItemPositions = new int[yourNumberOfColumns];
int pastVisiblesItems = layoutManager.findFirstVisibleItemPositions(firstVisibleItem‌​Positions)[0];

---

如果您使用的是StaggedGridLayoutManager，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;
            }
        }
    });

int visibleThreshold=1；
最终StaggedGridLayoutManager linearLayoutManager=（StaggedGridLayoutManager）mrecyclServiceWallPost.getLayoutManager（）；
mrecycleServiceWallPost.addOnScrollListener（新的RecycleView.OnScrollListener（）{
@凌驾
已填空的公共空间（RecyclerView RecyclerView、int dx、int dy）{
super.onScrolled（recyclerView、dx、dy）；
int[]lastVisibleItemPositions=linearLayoutManager.findLastVisibleItemPositions（null）；
int lastVisibleItem=getLastVisibleItem（lastVisibleItemPositions）；
int totalItemCount=linearLayoutManager.getItemCount（）；
如果（！isLoading&&totalItemCount maxSize）{
maxSize=lastVisibleItemPositions[i]；
}
}
返回最大大小；
}

您可以这样尝试：

StaggeredGridLayoutManager staggeredGridLayoutManager = (StaggeredGridLayoutManager) recyclerView.getLayoutManager();

或者，您可以直接使用

staggeredlayoutManager

对象，而不是上面的对象：

int[] into = staggeredGridLayoutManager .findLastVisibleItemPositions(null);
List<Integer> intoList = new ArrayList<>();

for (int i : into) 
{
 intoList.add(i);
}



int firstVisbleoitem= Collections.max(intoList);

int[]into=StaggedGridLayoutManager.findLastVisibleItemPositions（null）；
List intoList=新的ArrayList（）；
for（int i:into）
{
添加（i）；
}
int firstvisibleoitem=Collections.max（intoList）；

使用以下两种方法：

    /**
     * @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;
    }

---

我猜这是在第一次初始化时发生的。现在，在调用findFirstVisible之前检查它是否有子项，如果您能在b.android.com上创建一个bug报告也会很好。这个解决方案对我有效。请告诉我解决方案中是否有错误。layoutManager.findFirstVisibleItemPositions（null）将返回一个新数组。如果您正在使用类似StaggedGridLayoutManager（）的内容，则该方法的签名将更改。{currentScrollPosition=（recyclerView？.layoutManager作为StaggedGridLayoutManager）。findLastCompletelyVisibleItemPositions（intArrayOf（0,1））[1]}for kotlin use

val positionView=（recyclerView.layoutManager作为LinearLayoutManager）。findFirstVisibleItemPosition（）

    /**
     * @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;
    }

                    int[] lastVisibleItemPositions = ((StaggeredGridLayoutManager) layoutManager).findLastVisibleItemPositions(null);
                    int[] firstVisibleItemPositions = ((StaggeredGridLayoutManager) layoutManager).findFirstVisibleItemPositions(null);
                    // get maximum element within the list
                    lastVisibleItem = getLastVisibleItem(lastVisibleItemPositions);
                    firstVisibleItem = getFirstVisibleItem(firstVisibleItemPositions);