findFirstVisibleItemPositions 不适用于 recycleview android

Question

我有这个代码：

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];
    }
});

当我滚动回收视图时，出现此错误：

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

我该如何处理此错误并获取第一个可见项目的位置？

Answer 1

我用这段代码测试了它，它对我来说工作得很好

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

我使用了回收视图参数。

Answer 2

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 );

Answer 3

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);

Answer 4

您可以使用这个：

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

Answer 5

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;
}

Answer 6

如果您使用 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;
}

Answer 7

你可以这样尝试：

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

或者您可以直接使用您的

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);

Answer 8

在 Kotlin 中使用它：

val positionView = (recyclerView.layoutManager as LinearLayoutManager?)!!.findFirstVisibleItemPosition()

就这个。