Question

我在mRecyclerView.setLayoutManager(layoutManager);

中遇到错误

以下是在进入活动时弹出的logcat错误：

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.setLayoutManager（android.support.v7.widget.RecyclerView $ LayoutManager）” 在com.example.lenovo.skanda.QuoteList.onCreate（QuoteList.java:36）

QuoteList.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

您的RecyclerView尚未分配，请交换以下内容：

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

Answer 2

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

#include <iostream>
#include "Point.h"
#include "Line.h"

using namespace std;

int main() {

    int x, y;
    int size;           // Some user defined size for the array
    Line line;

    Point a[size];      // Some points that are already filled

    // Push the data in a[] to the variable "line"
    for(int i = 0; i < size; i++){
        // Increase array size of Point* points in variable line and add a[i] to the end of the array
        line.push(points[i]);
    }

    return 0;
}

Answer 3

当LinearLayout在布局中找不到RecyclerView时，就会发生这种情况。您必须在要显示列表的布局文件中添加RecyclerView，否则，在使用RecyclerView或未使用findViewById(R.id.recyclerviewID)时会错误地提及创建的RecyclerView。

RecyclerView setLayoutManager的logcat错误

3 个答案: