Question

我有一个电影应用程序，其中一个名为“正在显示”的列表项将打开一个新活动，以加载从我的Firebase电影数据库中拍摄的电影列表。但是，当我按“现在显示”时，该应用程序将崩溃。这是我的密码

public class NowShowing extends AppCompatActivity {

    RecyclerView movieRecyclerView;
    FirebaseDatabase movieFirebaseDatabase;
    DatabaseReference moviesRef;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_now_showing);
            //recyclerview
        movieRecyclerView = findViewById(R.id.listnowshowingmovies);
        movieRecyclerView.setAdapter(adapter);
        movieRecyclerView.setLayoutManager(new GridLayoutManager(this, 1));
            //send query to Firebasedatabase
        movieFirebaseDatabase = FirebaseDatabase.getInstance();
        moviesRef = movieFirebaseDatabase.getReference("Data");
    }
    //load data into recyclerview onstart
    FirebaseRecyclerOptions <movies> options =
            new FirebaseRecyclerOptions.Builder<movies>().setQuery(moviesRef, movies.class).build();

    FirebaseRecyclerAdapter adapter = new FirebaseRecyclerAdapter<movies, ViewHolder>( options ) {
        @NonNull
        @Override
        public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

            View view= LayoutInflater.from(parent.getContext()).inflate(R.layout.movies_cardview_all,parent,false);

            return new ViewHolder(view);
        }

        @Override
        protected void onBindViewHolder(@NonNull ViewHolder holder, int position, @NonNull movies model) {

            holder.setDetails(getApplicationContext(), model.getMovieTitle(),model.getMovieThumbnail(),model.getMovieSynopsis(),model.getMovieReleaseDate(),model.getMovieGenre(),
                    model.getMovieCast(),model.getMovieAgeRestriction(),model.getMovieRating());
        }
    };
}

这是我得到的错误

ava.lang.RuntimeException：无法启动活动ComponentInfo {com.example.ethan.premovies / com.example.ethan.premovies.NowShowing}：java.lang.NullPointerException：尝试调用虚拟方法'void android.support .v7.widget.RecyclerView.setAdapter（android.support.v7.widget.RecyclerView $ Adapter）'在空对象引用上在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:3254）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3350）在android.app.ActivityThread.access $ 1100（ActivityThread.java:222）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1795）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:158）在android.app.ActivityThread.main（ActivityThread.java:7229）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1230）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1120）引起原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void android.support.v7.widget.RecyclerView.setAdapter（android.support.v7.widget.RecyclerView $ Adapter）' 在com.example.ethan.premovies.NowShowing.onCreate（NowShowing.java:30）在android.app.Activity.performCreate（Activity.java:6876）在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1135）在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:3207）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3350）在android.app.ActivityThread.access $ 1100（ActivityThread.java:222）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1795）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:158）在android.app.ActivityThread.main（ActivityThread.java:7229）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1230）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1120）

我非常需要帮助，因为我仍然需要进行审核。我只是一个初学者，我才知道这一点。我的学校不费心教我们，所以我不得不找出自己。我也在寻找一些人来指导我参加Firebase。谢谢！

Answer 1

movieRecyclerView.setAdapter(adapter);

adapter调用时为null。它需要使用FirebaseRecyclerAdapter将提供的信息实例化，但是从提供的代码中看，它就像适配器是在您尝试调用它之后创建的。

Answer 2

RecyclerView movieRecyclerView;
FirebaseDatabase movieFirebaseDatabase;
DatabaseReference moviesRef;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_now_showing);
        //recyclerview
    movieRecyclerView = findViewById(R.id.listnowshowingmovies);
    movieRecyclerView.setAdapter(adapter);
    movieRecyclerView.setLayoutManager(new GridLayoutManager(this, 1));
        //send query to Firebasedatabase
    movieFirebaseDatabase = FirebaseDatabase.getInstance();
    moviesRef = movieFirebaseDatabase.getReference("Data");

    //load data into recyclerview in onCreate
    FirebaseRecyclerOptions <movies> options =
        new FirebaseRecyclerOptions.Builder<movies>().setQuery(moviesRef, movies.class).build();

    FirebaseRecyclerAdapter adapter = new FirebaseRecyclerAdapter<movies, ViewHolder>( options ) {
        @NonNull
        @Override
        public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

            View view= LayoutInflater.from(parent.getContext()).inflate(R.layout.movies_cardview_all,parent,false);

            return new ViewHolder(view);
        }

        @Override
        protected void onBindViewHolder(@NonNull ViewHolder holder, int position, @NonNull movies model) {

            holder.setDetails(getApplicationContext(), model.getMovieTitle(),model.getMovieThumbnail(),model.getMovieSynopsis(),model.getMovieReleaseDate(),model.getMovieGenre(),

            model.getMovieCast(),model.getMovieAgeRestriction(),model.getMovieRating());
        }
    });
}

按照上面的步骤在onCreate（）中移动代码。

如何在Firebase recyclerview上设置SetAdapter？

2 个答案: