在RecyclerView setLayoutManager的logcat中出错

Question

我在mRecyclerView.setLayoutManager(layoutManager);得到错误

以下是进入活动时弹出的logcat错误：

引起：java.lang.NullPointerException：尝试在com.example的空对象引用上调用虚方法'void android.support.v7.widget.RecyclerView.setLayoutManager（android.support.v7.widget.RecyclerView $ LayoutManager）' .lenovo.skanda.QuoteList.onCreate（QuoteList.java:36）

quote list.Java

public class QuoteList extends AppCompatActivity {

    private StorageReference storageRef;

    RecyclerView  mRecyclerView;
    FirebaseDatabase mFirebaseDatabase;
    DatabaseReference mReference;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_quote_list);

        //ActionBar actionBar = getSupportActionBar();
        //getSupportActionBar().setTitle("Quotes");
        //getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        //getSupportActionBar().setHomeButtonEnabled(true);

        final LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        mRecyclerView.setLayoutManager(layoutManager);

        mRecyclerView = findViewById(R.id.recyclerViewQuote);
       // mRecyclerView.setHasFixedSize(true);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));

        mFirebaseDatabase = FirebaseDatabase.getInstance();
        mReference = mFirebaseDatabase.getReference("Quotes");
    }





    @Override
    protected void onStart() {
        super.onStart();

        FirebaseRecyclerAdapter<Quote, QuoteViewHolder> firebaseRecyclerAdapter =
                new FirebaseRecyclerAdapter<Quote, QuoteViewHolder>(
                        Quote.class,
                        R.layout.quote_row,
                        QuoteViewHolder.class,
                        mReference
                ) {

                    @Override
                    protected void populateViewHolder(QuoteViewHolder viewHolder , Quote model , int position) {

                     //   viewHolder.setDetails(getApplicationContext(), model.getQuotes(), model.getQuote_Author(), model.getImages());
                            viewHolder.setQuotes(model.getQuotes());
                            viewHolder.setQuoteAuthor(model.getQuote_Author());


                    }
                };

        mRecyclerView.setAdapter(firebaseRecyclerAdapter);

    }

    public static class QuoteViewHolder extends RecyclerView.ViewHolder{

        View mView;

        public QuoteViewHolder(View itemView) {
            super(itemView);

            mView = itemView;
        }

        public void setQuotes(String Quote){
            TextView post_quote = (TextView) mView.findViewById(R.id.post_quote);
            post_quote.setText(Quote);
        }

        public void setQuoteAuthor(String QuoteAuthor){
            TextView post_quoteAuthor = (TextView) mView.findViewById(R.id.post_author);
            post_quoteAuthor.setText(QuoteAuthor);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        getMenuInflater().inflate(R.menu.main_menu, menu);
        return super.onCreateOptionsMenu(menu);
    }
}

请帮帮我。

Answer 1

你的RecyclerView尚未分配，交换这些：

mRecyclerView = findViewById(R.id.recyclerViewQuote);
mRecyclerView.setLayoutManager(layoutManager);

Answer 2

请编写这样的代码，首先需要在Linear Layout Manager之前初始化recyclerview。

 mRecyclerView = findViewById(R.id.recyclerViewQuote);

 final LinearLayoutManager layoutManager = new LinearLayoutManager(this);
    layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
    mRecyclerView.setLayoutManager(layoutManager);