我们的应用上有 ViewPager FragmentPagerAdapter 包含三个 fragment 。其中两个 fragment 由 Recyclerview 组成。每一个。
第一页(没有 ViewPager 的 fragment )正确显示。但是，当 ViewPager 尝试预加载下一页(RecyclerView)时，应用程序由于 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。
最佳答案
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 fragment View 上崩溃。
关于android - 带有 Recyclerview 的 ViewPager 上的 NullPointerException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/32691513/