带有 Recyclerview 的 ViewPager 上的 NullPointerException
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【中文标题】带有 Recyclerview 的 ViewPager 上的 NullPointerException【英文标题】:NullPointerException on ViewPager with Recyclerview 【发布时间】:2015-12-17 22:25:24 【问题描述】:我们的应用程序上有一个ViewPager 和一个FragmentPagerAdapter
,其中包含三个片段。其中两个片段由一个Recyclerview 组成。
第一页(没有 ViewPager 的片段)正确显示。但是,当 ViewPager 尝试预加载下一页(RecyclerView)时,应用程序会因为NullPointerException
而崩溃,日志如下:
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.v7.widget.RecyclerView$ViewHolder.shouldIgnore()' on a null object reference
at android.support.v7.widget.RecyclerView.findMinMaxChildLayoutPositions(RecyclerView.java:2839)
at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:2626)
at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:3011)
at android.view.View.layout(View.java:15684)
at android.view.ViewGroup.layout(ViewGroup.java:4981)
at android.support.v4.view.ViewPager.onLayout(ViewPager.java:1626)
at android.view.View.layout(View.java:15684)
at android.view.ViewGroup.layout(ViewGroup.java:4981)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
at android.view.View.layout(View.java:15684)
at android.view.ViewGroup.layout(ViewGroup.java:4981)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
at android.view.View.layout(View.java:15684)
at android.view.ViewGroup.layout(ViewGroup.java:4981)
at android.support.design.widget.CoordinatorLayout.layoutChild(CoordinatorLayout.java:1000)
at android.support.design.widget.CoordinatorLayout.onLayoutChild(CoordinatorLayout.java:710)
at android.support.design.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:724)
at android.view.View.layout(View.java:15684)
at android.view.ViewGroup.layout(ViewGroup.java:4981)
at android.support.v4.widget.DrawerLayout.onLayout(DrawerLayout.java:907)
at android.view.View.layout(View.java:15684)
at android.view.ViewGroup.layout(ViewGroup.java:4981)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
at android.view.View.layout(View.java:15684)
at android.view.ViewGroup.layout(ViewGroup.java:4981)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
at android.view.View.layout(View.java:15684)
at android.view.ViewGroup.layout(ViewGroup.java:4981)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
at android.view.View.layout(View.java:15684)
at android.view.ViewGroup.layout(ViewGroup.java:4981)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
at android.view.View.layout(View.java:15684)
at android.view.ViewGroup.layout(ViewGroup.java:4981)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
at android.view.View.layout(View.java:15684)
at android.view.ViewGroup.layout(ViewGroup.java:4981)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2186)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1920)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1106)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6018)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:792)
at android.view.Choreographer.doCallbacks(Choreographer.java:596)
at android.view.Choreographer.doFrame(Choreographer.java:557)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:778)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:155)
at android.app.ActivityThread.main(ActivityThread.java:5696)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
ViewPager 的声明方式如下:
ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFrag(fragment1, "fragment1");
adapter.addFrag(fragment2, "fragment2");
adapter.addFrag(fragment3, "fragment3");
viewPager.setAdapter(adapter);
还有适配器:
private class ViewPagerAdapter extends FragmentPagerAdapter
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager)
super(manager);
@Override
public Fragment getItem(int position)
return mFragmentList.get(position);
@Override
public int getCount()
return mFragmentList.size();
public void addFrag(Fragment fragment, String title)
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
@Override
public CharSequence getPageTitle(int position)
return mFragmentTitleList.get(position);
由于两个 RecyclerView 的代码都很长并且每个页面都不同,我真的不知道哪个部分是相关的,所以我不会给出任何示例。如果您认为对解决问题有帮助,请随时提出具体要求。
我可以告诉你的一件事是,如果我想让它工作,我必须评论来自 RecylerView 的每个 setAdapter
的调用。
编辑:这是第二页的代码。
public class MyFragment extends Fragment
RecyclerView recyclerView;
GridAdapter gridAdapter;
public GridAdapter getGridAdapter()
return gridAdapter;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
final View v = inflater.inflate(R.layout.our_layout, container, false);
recyclerView = (RecyclerView) v.findViewById(R.id.recycler_view);
gridLayoutManager.setSmoothScrollbarEnabled(true);
recyclerView.setLayoutManager(gridLayoutManager);
recyclerView.setHasFixedSize(true);
return v;
@Override
public void onActivityCreated(Bundle savedInstanceState)
super.onActivityCreated(savedInstanceState);
ArrayList<Model> model = getArguments().getParcelableArrayList("extra");
if (model != null && model.size() != 0)
gridAdapter = new GridAdapter(model);
recyclerView.setAdapter(gridAdapter);
@Override
public void setUserVisibleHint(boolean isVisibleToUser)
super.setUserVisibleHint(isVisibleToUser);
if (isVisibleToUser && isResumed())
onResume();
@Override
public void onResume()
super.onResume();
if (!getUserVisibleHint())
return;
public class GridSpacingItemDecoration extends RecyclerView.ItemDecoration
private int spanCount;
private int spacingLeft;
private int spacingRight;
private int spacingTop;
private int spacingBottom;
private boolean includeEdge;
public GridSpacingItemDecoration(int spanCount, int spacingLeft, int spacingTop, int spacingRight, int spacingBottom, boolean includeEdge)
this.spanCount = spanCount;
this.spacingLeft = spacingLeft;
this.spacingRight = spacingRight;
this.spacingTop = spacingTop;
this.spacingBottom = spacingBottom;
this.includeEdge = includeEdge;
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state)
int position = parent.getChildAdapterPosition(view); // item position
int column = position % spanCount; // item column
if (includeEdge)
outRect.left = spacingLeft - column * spacingLeft / spanCount; // spacing - column * ((1f / spanCount) * spacing)
outRect.right = (column + 1) * spacingRight / spanCount; // (column + 1) * ((1f / spanCount) * spacing)
if (position < spanCount) // top edge
outRect.top = spacingTop;
outRect.bottom = spacingBottom; // item bottom
else
outRect.left = column * spacingLeft / spanCount; // column * ((1f / spanCount) * spacing)
outRect.right = spacingRight - (column + 1) * spacingRight / spanCount; // spacing - (column + 1) * ((1f / spanCount) * spacing)
if (position >= spanCount)
outRect.top = spacingTop; // item top
public class GridAdapter extends RecyclerView.Adapter<GridAdapter.ViewHolder>
private ArrayList<Model> model;
public GridAdapter(ArrayList<Model> offer)
super();
model = offer;
@Override
public ViewHolder onCreateViewHolder(final ViewGroup parent, int viewType)
final View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.layout_item, parent, false);
final ViewHolder holder = new ViewHolder(view);
return holder;
@Override
public void onBindViewHolder(final ViewHolder holder, final int position)
final Model currentOffer = model.get(position);
holder.category.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener()
@SuppressLint("NewApi")
@SuppressWarnings("deprecation")
@Override
public void onGlobalLayout()
int width = holder.category.getWidth();
ViewGroup.LayoutParams params = holder.appIcon.getLayoutParams();
params.width = width;
params.height = width;
holder.appIcon.setLayoutParams(params);
if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.JELLY_BEAN)
holder.itemView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
else
holder.itemView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
);
Picasso.with(getActivity().getApplicationContext()).
load(currentOffer.getApp_logo()).fit().centerCrop().into(holder.appIcon);
holder.appName.setText(currentOffer.getApp_name());
holder.category.setText(currentOffer.getApp_category());
holder.itemView.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View v)
String marketURL = AndroidTools.getPlayStoreURL(currentOffer.getApp_store_id(), true);
UITools.launchUrl(getActivity(), marketURL);
);
@Override
public int getItemCount()
return model.size();
class ViewHolder extends RecyclerView.ViewHolder
private ImageView appIcon;
private TextView appName;
private TextView category;
public ViewHolder(View itemView)
super(itemView);
appIcon = (ImageView)itemView.findViewById(R.id.item_icon);
appName = (TextView)itemView.findViewById(R.id.item_app_name);
category = (TextView)itemView.findViewById(R.id.item_category);
非常感谢任何帮助。
【问题讨论】:
第三个片段有没有recyclerView? [EDITED]对不起,它在那里。你能发布你的第二个片段的代码 首页是一个没有任何RecyclerView的片段。但是,是的,第二个和第三个是片段,每个片段都由一个 RecyclerView 组成。 您可以发布您的适配器的onBindViewHolder()
方法吗?
请发布您的第二个片段的代码
附加到片段的数据是来自本地或静态数据还是来自服务器的数据
【参考方案1】:
我在开发过程中遇到了这个错误。您是否检查过您的 XML 文件中的 RecyclerView 是否正确包装到另一个布局中,例如 FrameLayout?
如果不是,它只会在 Viewpager 上崩溃,而不会在单个片段视图上崩溃。
【讨论】:
你是对的!我的布局只由一个 RecyclerView 组成,我不知道它必须包装在另一个中。感谢您的帮助! 在我的情况下,错误是由于不同的原因引起的。在这里查看我的答案:***.com/a/47436165/700693 我的 RecyclerView 中有一个随机的 TextView,只能在搞砸它的 XML 中查看。 你拯救了我的一天! :-) 但是“正确包装到另一个布局”是什么意思?有这方面的官方文档吗?【参考方案2】:当您不小心将视图直接添加到 RecyclerView
时,就会发生这种情况。在我的例子中,我使用View.inflate
作为装饰器布局,将RecyclerView
作为父参数,它会自动附加它。 RecyclerView
遍历附加到它的所有子视图,并期望其所有视图子视图在布局参数中具有 ViewHolders
,并且当子视图持有者为空时将抛出此 NPE。
【讨论】:
【参考方案3】:当您在 xml 布局 文件中直接在 listView
或 RecyclerView
下添加 元素时,会发生这种情况。
<android.support.v7.widget.RecyclerView
android:layout_
android:layout_
android:scrollbars="vertical">
<TextView
android:layout_
android:layout_ />
</android.support.v7.widget.RecyclerView>
在这里,我在 RecyclerView 中添加了一个 TextView,它会抛出我 onLayout error
(由 NullPointerException
引起)。你不应该直接在 RecyclerView
或 listView
下添加元素。
【讨论】:
这对我来说是个错误。删除子 RecyclerView 的元素后,它就像一个魅力。这个NullPointerException
是一个描述性错误。【参考方案4】:
在回收站视图中添加 no children 并将 attachToRoot
(inflate()
方法的第三个参数)设置为 false
,同时为我添加自定义布局.
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType)
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.online_user, parent, false);
return new RecyclerViewHolder(view.findViewById(R.id.onlineUserView));
布局:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_
android:layout_
android:orientation="vertical">
<android.support.v7.widget.RecyclerView
android:id="@+id/onlineUsersView"
android:layout_
android:layout_ />
</LinearLayout>
【讨论】:
【参考方案5】:变化:
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
到:
// remove final keyword
private List<Fragment> mFragmentList = new ArrayList<>();
private List<String> mFragmentTitleList = new ArrayList<>();
最终变量不会取任何值,即使您尝试添加它们。
【讨论】:
哦。然后不用一一添加,而是将完整的列表发送给Adapter,在adapter中全部添加到列表中。 这不是“最终变量”的工作方式。您可以在列表中添加和删除项目,即使它已声明为最终项目。 是的,斯科特说的;列表不是它拥有的对象;将这些对象分类为一个集合是最终的。想象一下,您将如何根据列表的最终确定性来断言列表中项目的字段是最终的,您就会明白为什么在保持任何表面性能的同时无法做到这一点。以上是关于带有 Recyclerview 的 ViewPager 上的 NullPointerException的主要内容,如果未能解决你的问题,请参考以下文章
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