我创建了一个电影应用程序，用于在themoviedb.org查询 REST API 。在从网格中选择电影时，用户将进入详细信息屏幕，其中显示有关电影的更多详细信息，其中包含预告片列表和评论列表。问题是 SOMETIMES 我填写评论和预告片列表的代码点击NullPointerException 。它并不总是发生，并且它不是特定的电影条目，它是完全随机的。
准确地说，当我在成功的网络响应后使用runOnUIThread（）内的数据刷新我的RecyclerView适配器时，我会随机获取NullPointerExceptions。
这是GitHub回购链接 - https://github.com/Hackertronix/Project-Motion/tree/Stage_2
以下是我的代码以及堆栈跟踪
我添加了评论以显示行号
DetailsFragment.java
package com.execube.genesis.views.fragments;
import android.annotation.TargetApi;
import android.content.Intent;
import android.graphics.Color;
import android.graphics.Typeface;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.design.widget.CoordinatorLayout;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.app.Fragment;
import android.support.v4.content.ContextCompat;
import android.support.v7.widget.CardView;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.RatingBar;
import android.widget.TextView;
import android.widget.Toast;
import com.execube.genesis.R;
import com.execube.genesis.model.Event;
import com.execube.genesis.model.Movie;
import com.execube.genesis.model.Review;
import com.execube.genesis.model.Trailer;
import com.execube.genesis.utils.API;
import com.execube.genesis.utils.EventBus;
import com.execube.genesis.utils.JSONParser;
import com.execube.genesis.utils.OkHttpHandler;
import com.orm.SugarRecord;
import com.squareup.picasso.Picasso;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import okhttp3.Call;
import okhttp3.Response;
import static com.execube.genesis.R.drawable.ic_favorite_black_24dp;
/**
* Created by Prateek Phoenix on 4/30/2016.
*/
public class DetailsFragment extends Fragment {
private static final String TAG = "DETAILS";
private static final int DEFAULT_NUM_COLORS = 5;
private Movie mMovie;
private Movie entry,tempMovie;
private List<Movie> movie;
public Intent intent;
private TextView mDetailTitle;
private TextView mReleaseDate;
private TextView mOverview;
private TextView mOverviewHeader;
private TextView mReviesHeader;
private TextView mTrailersHeader;
private ImageView mBackdrop;
private Toolbar mToolbar;
private RatingBar mRatingBar;
private ArrayList<Review> mReviews=new ArrayList<>();
private ArrayList<Trailer> mTrailers=new ArrayList<>();
private List<Movie> updatedFavsList= new ArrayList<>();
public static final String MOVIE_REVIEWS_ARRAY ="movie_details";
private static final String MOVIE_TRAILERS_ARRAY = "movie_reviews";
private Typeface fontBold;
private Typeface fontMediumLight;
private Typeface fontMedium;
private RecyclerView mReviewRecyclerView;
private RecyclerView mTrailerRecyclerView;
private ProgressBar mReviewsProgressbar;
private ProgressBar mTrailersProgressbar;
private CoordinatorLayout mCoordinatorLayout;
private CardView mReviewsCardView;
private FloatingActionButton mFloatingActionButton;
private ReviewsAdapter mReviewAdapter;
private int NumOfReviews;
private TrailersAdapter mTrailerAdapter;
private String id;
private boolean isFav;
public DetailsFragment() {
}
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public void onSaveInstanceState(Bundle outState) {
Log.v(TAG,"Saving state in onSaveInstanceState");
outState.putParcelableArrayList(MOVIE_REVIEWS_ARRAY,mReviews);
outState.putParcelableArrayList(MOVIE_TRAILERS_ARRAY,mTrailers);
super.onSaveInstanceState(outState);
}
@TargetApi(Build.VERSION_CODES.LOLLIPOP)
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_detail, container, false);
mBackdrop = (ImageView) view.findViewById(R.id.details_poster);
mDetailTitle = (TextView) view.findViewById(R.id.detail_title_text);
mReleaseDate = (TextView) view.findViewById(R.id.release_date);
mOverview = (TextView) view.findViewById(R.id.overview);
mOverviewHeader = (TextView) view.findViewById(R.id.overview_header);
mReviesHeader=(TextView)view.findViewById(R.id.review_header);
mTrailersHeader=(TextView)view.findViewById(R.id.trailer_header);
mRatingBar = (RatingBar) view.findViewById(R.id.movie_rating);
mCoordinatorLayout=(CoordinatorLayout)view.findViewById(R.id.coordinator_layout);
mReviewRecyclerView= (RecyclerView)view.findViewById(R.id.review_recycler_view);
mTrailerRecyclerView=(RecyclerView)view.findViewById(R.id.trailer_recycler_view);
mReviewsProgressbar=(ProgressBar)view.findViewById(R.id.reviews_progressbar);
mTrailersProgressbar=(ProgressBar)view.findViewById(R.id.trailers_progressbar);
mFloatingActionButton=(FloatingActionButton)view.findViewById(R.id.fab);
mReviewsCardView= (CardView) view.findViewById(R.id.reviews_card);
intent = getActivity().getIntent();
Bundle bundle=getArguments();
mMovie=bundle.getParcelable("PARCEL");
tempMovie=mMovie;
id = String.valueOf(mMovie.getMovieId());
checkFav();
mFloatingActionButton.show();
assert mMovie != null;
//PREPPING THE URL FOR QUERY
String reviewQueryUrl = API.MOVIES_BASE_URL + id + "/reviews" + API.API_KEY;
String trailerQueryUrl = API.MOVIES_BASE_URL + id + "/videos" + API.API_KEY;
mDetailTitle.setText(mMovie.getTitle());
mReleaseDate.setText(mMovie.getReleaseDate());
mRatingBar.setProgress((int) mMovie.getVoteAverage());
mOverview.setText(mMovie.getOverview());
if (Build.VERSION.SDK_INT != 21) {
fontBold = Typeface.createFromAsset(getActivity().getAssets(), "fonts/Gotham-Rounded-Bold.ttf");
fontMedium = Typeface.createFromAsset(getActivity().getAssets(), "fonts/Gotham-Rounded-Medium.ttf");
fontMediumLight = Typeface.createFromAsset(getActivity().getAssets(), "fonts/Gotham-Rounded-Book_.ttf");
mDetailTitle.setTypeface(fontBold);
mReleaseDate.setTypeface(fontMedium);
mOverview.setTypeface(fontMediumLight);
mOverviewHeader.setTypeface(fontBold);
mReviesHeader.setTypeface(fontBold);
mTrailersHeader.setTypeface(fontBold);
}
//FETCHING JSON HERE
if(savedInstanceState!=null&&savedInstanceState.containsKey(MOVIE_REVIEWS_ARRAY))
{
Log.v(TAG,"Restoring from bundle");
mReviews=savedInstanceState.getParcelableArrayList(MOVIE_REVIEWS_ARRAY);
mTrailers=savedInstanceState.getParcelableArrayList(MOVIE_TRAILERS_ARRAY);
mReviewsProgressbar.setVisibility(View.GONE);
mTrailersProgressbar.setVisibility(View.GONE);
}
else {
OkHttpHandler reviewsHandler = new OkHttpHandler(reviewQueryUrl, reviewsCallback);
reviewsHandler.fetchData();
OkHttpHandler trailersHandler= new OkHttpHandler(trailerQueryUrl, trailersCallback);
trailersHandler.fetchData();
}
Picasso.with(getActivity()).load(API.IMAGE_URL + API.IMAGE_SIZE_500 + mMovie.getPosterPath())
.placeholder(R.drawable.placeholder)
.error(R.drawable.error)
.into(mBackdrop);
getActivity().startPostponedEnterTransition();
mReviewRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
mReviewAdapter= new ReviewsAdapter();
mReviewRecyclerView.setAdapter(mReviewAdapter);
LinearLayoutManager layoutmanager= new LinearLayoutManager(getActivity(),LinearLayoutManager.HORIZONTAL,false);
mTrailerRecyclerView.setLayoutManager(layoutmanager);
mTrailerAdapter= new TrailersAdapter();
mTrailerRecyclerView.setAdapter(mTrailerAdapter);
return view;
}
private void checkFav() {
movie=new ArrayList<>();
movie=SugarRecord.find(Movie.class,"m_id=?",id);
if(movie.size()==0)
{
Log.v(TAG,"Null");
mFloatingActionButton.setImageResource(R.drawable.ic_favorite_border_black_24dp);
}
else {
Log.v(TAG,"NOT Null");
mFloatingActionButton.setImageResource(R.drawable.ic_favorite_black_24dp);
}
mFloatingActionButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
movie=SugarRecord.find(Movie.class,"m_id=?",id);
if(movie.size()>0)
{
entry = movie.get(0);
entry.delete();
Event event = new Event("Database has been modified!!");
EventBus.getBus().post(event);
mFloatingActionButton.setImageResource(R.drawable.ic_favorite_border_black_24dp);
Snackbar snackbar = Snackbar.make(mCoordinatorLayout,"Movie removed from Favourites!!",Snackbar.LENGTH_SHORT);
View view= snackbar.getView();
TextView textView = (TextView)view.findViewById(android.support.design.R.id.snackbar_text);
textView.setTextColor(Color.YELLOW);
snackbar.show();
}
else
{
entry = tempMovie;
entry.save();
Event event = new Event("Database has been modified!!");
EventBus.getBus().post(event);
mFloatingActionButton.setImageResource(R.drawable.ic_favorite_black_24dp);
Snackbar snackbar = Snackbar.make(mCoordinatorLayout,"Movie added to Favourites!!",Snackbar.LENGTH_SHORT);
View view= snackbar.getView();
TextView textView = (TextView)view.findViewById(android.support.design.R.id.snackbar_text);
textView.setTextColor(Color.YELLOW);
snackbar.show();
}
}
});
}
//OKHTTP CALLBACK FOR NETWORK CALL
private okhttp3.Callback reviewsCallback = new okhttp3.Callback() {
@Override
public void onFailure(Call call, IOException e) {
//TODO handle failure on UI thread
}
@Override
public void onResponse(Call call, Response response) throws IOException {
try {
String JSONData= response.body().string();
JSONObject jsonObject = new JSONObject(JSONData);
NumOfReviews = jsonObject.getInt("total_results");
JSONParser parser = new JSONParser();
mReviews=parser.parseReviews(JSONData);
} catch (JSONException e) {}
getActivity().runOnUiThread(new Runnable() {
@Override //THIS IS THE FIRST LINE WHERE I GET A NULL POINTER EXCEPTION
public void run() {
if(mReviewAdapter!=null)
{
mReviewsProgressbar.setVisibility(View.GONE);
mReviewAdapter.notifyDataSetChanged();
}
}
});
getActivity().runOnUiThread(new Runnable() {
@Override
public void run() {
if (NumOfReviews==0)
{
mReviewsCardView.setVisibility(View.INVISIBLE);
}
}
});
}
};
private okhttp3.Callback trailersCallback = new okhttp3.Callback() {
@Override
public void onFailure(Call call, IOException e) {
//TODO handle failure on UI thread
}
@Override
public void onResponse(Call call, Response response) throws IOException {
try {
String json1= response.body().string();
JSONParser parser= new JSONParser();
mTrailers = parser.parseTrailers(json1);
} catch (JSONException e) {}
getActivity().runOnUiThread(new Runnable() {
@Override
public void run() { //THIS IS THE 2nd LINE WHERE I GET A NULL POINTER EXCEPTION
if(mTrailerAdapter!=null)
{
mTrailersProgressbar.setVisibility(View.GONE);
mTrailerAdapter.notifyDataSetChanged();
}
}
});
}
};
private class ReviewViewHolder extends RecyclerView.ViewHolder{
private TextView mAuthorText;
private TextView mReviewText;
private Review mReview;
public ReviewViewHolder(View itemView) {
super(itemView);
mAuthorText= (TextView) itemView.findViewById(R.id.author_textview);
mReviewText= (TextView) itemView.findViewById(R.id.review_textview);
}
public void bind(Review review)
{
mReview= review;
mAuthorText.setText(mReview.getAuthor());
mReviewText.setText(mReview.getContent());
if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.LOLLIPOP)
{
mAuthorText.setTypeface(fontBold);
mReviewText.setTypeface(fontMediumLight);
}
}
}
private class ReviewsAdapter extends RecyclerView.Adapter<ReviewViewHolder>{
@Override
public ReviewViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view= LayoutInflater.from(getActivity()).inflate(R.layout.review_item,parent,false);
return new ReviewViewHolder(view);
}
@Override
public void onBindViewHolder(ReviewViewHolder holder, int position) {
Review review= mReviews.get(position);
holder.bind(review);
}
@Override
public int getItemCount() {
if(mReviews==null)
{ return 0;}
else
{return mReviews.size();}
}
}
private class TrailerViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
private ImageView mTrailerThumbnail;
private Trailer mTrailer;
public TrailerViewHolder(View itemView) {
super(itemView);
mTrailerThumbnail=(ImageView)itemView.findViewById(R.id.trailer_thumbnail);
itemView.setOnClickListener(this);
}
public void bind(Trailer trailer)
{
mTrailer=trailer;
Picasso picasso =Picasso.with(getActivity());
picasso.setIndicatorsEnabled(true);
picasso.load(API.YOUTUBE_THUMBNAIL_URL+mTrailer.getKey()+API.THUMBNAIL_QUALITY)
.into(mTrailerThumbnail);
}
@Override
public void onClick(View v) {
Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(API.YOUTUBE_TRAILER_URL+mTrailer.getKey()));
startActivity(intent);
}
}
private class TrailersAdapter extends RecyclerView.Adapter<TrailerViewHolder>
{
@Override
public TrailerViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view= LayoutInflater.from(getActivity()).inflate(R.layout.trailer_item,parent,false);
return new TrailerViewHolder(view);
}
@Override
public void onBindViewHolder(TrailerViewHolder holder, int position) {
Trailer trailer= mTrailers.get(position);
holder.bind(trailer);
}
@Override
public int getItemCount() {
return mTrailers.size();
}
}
}
堆栈跟踪
06-10 02:02:30.548 25094-27219/? E/AndroidRuntime: FATAL EXCEPTION: OkHttp Dispatcher
Process: com.execube.genesis, PID: 25094
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.app.FragmentActivity.runOnUiThread(java.lang.Runnable)' on a null object reference
at com.execube.genesis.views.fragments.DetailsFragment$3.onResponse(DetailsFragment.java:349)
at okhttp3.RealCall$AsyncCall.execute(RealCall.java:133)
at okhttp3.internal.NamedRunnable.run(NamedRunnable.java:32)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
at java.lang.Thread.run(Thread.java:818)
06-10 02:02:30.548 25094-27218/? E/AndroidRuntime: FATAL EXCEPTION: OkHttp Dispatcher
Process: com.execube.genesis, PID: 25094
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.app.FragmentActivity.runOnUiThread(java.lang.Runnable)' on a null object reference
at com.execube.genesis.views.fragments.DetailsFragment$2.onResponse(DetailsFragment.java:308)
at okhttp3.RealCall$AsyncCall.execute(RealCall.java:133)
at okhttp3.internal.NamedRunnable.run(NamedRunnable.java:32)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
at java.lang.Thread.run(Thread.java:818)
答案 0 :(得分：4)
当您呼叫getActivity时，如果片段未附加到任何活动，则可能会返回null。为了避免使用NullPointerException，请务必首先检查它是否为null，然后继续使用您的逻辑。
if(getActivity!=null){
//do stuff
}