java findFirstVisibleItemPositions 不适用于 recycleview android

findFirstVisibleItemPositions doesn't work for recycleview android

提问by user3535747

I have this code:

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];
    }
});

When I scroll my recycleview I get this error:

当我滚动我的回收视图时，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.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

How can I do to handle this error and get the first visible item position?

我该如何处理这个错误并获得第一个可见的项目位置？

回答by zed007

I tested it with this code and it works fine with me

我用这段代码对其进行了测试，它对我来说很好用

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

I used the recycle view parameter.

我使用了回收视图参数。

回答by Ankit Aggarwal

Try this:

试试这个：

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

where layoutManageris what you set in your recyclerview.

这里layoutManager是你在你的设置recyclerview。

For example,

例如，

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

回答by user3793358

You can use this :

你可以使用这个：

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

回答by Mr.Hosseini

Use these two methods :

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;
    }

and getLastVisibleItem method as below:

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);

回答by varotariya vajsi

If you are using StaggeredGridLayoutManager you can find findLastVisibleItemPositionslike below:

如果您使用 StaggeredGridLayoutManager，您可以找到如下所示的findLastVisibleItemPositions：

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;
            }
        }
    });

and getLastVisibleItemmethod as below:

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;
}

回答by subhash gaikwad

You can try it this way:

你可以这样试试：

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

Or you can use your staggeredlayoutManagerobject directly instead of above object:

或者你可以staggeredlayoutManager直接使用你的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);

回答by TalkLittle

This is a bug in the RecyclerView StaggeredGridLayoutManager:

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=180521

https://code.google.com/p/android/issues/detail?id=181461

https://code.google.com/p/android/issues/detail?id=181461

A workaround is to try/catch the exception:

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;
}