Question

我很久以来一直坚持这个错误，我是JAVA的新手。我想点击从Firebase填充的RecyclerView（当前在片段上）上的项目。一旦我点击它，它应该通过分配一些数据和项目的位置来转到下一个片段。

这是我的适配器 CustomAdapter.java

    public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.MyViewHolder> {


public CustomAdapter(ArrayList<Userpost> data) {
    this.data = data;
}

public interface OnItemClickListener{
    void onItemClick(Userpost userpost, int activityNumber);
}




private ArrayList<Userpost> data;
private static final int ACTIVITY_NUM = 4;
private OnItemClickListener listener;


public class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener{

    TextView textViewName;
    TextView textViewVersion;
    SquareImageView imageView;
    private final Context context;
    public View mCardView;



    public MyViewHolder(View itemView) {
        super(itemView);
        context = itemView.getContext();
        this.textViewName = (TextView) itemView.findViewById(R.id.textViewName);
        this.textViewVersion = (TextView) itemView.findViewById(R.id.textViewVersion);
        this.imageView = (SquareImageView) itemView.findViewById(R.id.imageView);
        this.mCardView = itemView.findViewById(R.id.card_view);
        itemView.setOnClickListener(this);

    }
    @Override
    public void onClick(View v) {
        Toast.makeText(context, "Position is " +getAdapterPosition(),Toast.LENGTH_SHORT).show();
    }

}

@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent,
                                       int viewType) {

    Log.d(TAG, "MyViewHolder: setting up adapter for profile fragment");
    View itemView = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.cards_layout, parent, false);

    MyViewHolder myViewHolder = new MyViewHolder(itemView);
    return myViewHolder;
}


@Override
public void onBindViewHolder(final MyViewHolder holder, final int Position) {

    Log.d(TAG, "onBindViewHolder: setting up adapter for profile fragment");
    TextView textViewName = holder.textViewName;
    TextView textViewVersion = holder.textViewVersion;
    final ImageView imageView = holder.imageView;

    textViewName.setText(data.get(Position).getPheading());
    textViewVersion.setText(data.get(Position).getDescriptionpost());
    Picasso.with(holder.imageView.getContext()).load(data.get(Position).getImage_path()).into(holder.imageView);

    holder.itemView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Toast.makeText(view.getContext(), "Recycle Click" + Position, Toast.LENGTH_SHORT).show();
            listener.onItemClick(data.get(Position), ACTIVITY_NUM);

        }
    });

}

@Override
public int getItemCount() {
    return data.size();
}

}

这是片段， ProfileFragment.java

    public class ProfileFragment extends Fragment {

private static final String TAG = "ProfileFragment";
private static final int ACTIVITY_NUM = 4;  

//firebase stuff
private FirebaseAuth mAuth;
private FirebaseAuth.AuthStateListener mAuthListener;
private FirebaseDatabase mFirebaseDatabase;
private DatabaseReference myRef;
private FirebaseMethods mFirebaseMethods; 


// Recycler View Widgets
private static RecyclerView.Adapter adapter;
private RecyclerView.LayoutManager layoutManager;
private static RecyclerView recyclerView;
private static ArrayList<Userpost> data;
private static ArrayList<Integer> removedItems;

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_profile, container, false);

    gridView = (GridView) view.findViewById(R.id.gridView);
    recyclerView = (RecyclerView) view.findViewById(R.id.my_recycler_view);
    cardView = (CardView) view.findViewById(R.id.card_view);
    toolbar = (Toolbar) view.findViewById(R.id.profileToolBar);       
    bottomNavigationView = (BottomNavigationViewEx) view.findViewById(R.id.bottomNavViewBar);
    mContext = getActivity();
    mFirebaseMethods = new FirebaseMethods(getActivity());       


    //Recycler View class
    super.onCreate(savedInstanceState);
    data = new ArrayList<Userpost>();
    recyclerView = (RecyclerView) view.findViewById(R.id.my_recycler_view);
    recyclerView.setHasFixedSize(true);

    layoutManager = new LinearLayoutManager(getActivity());
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setItemAnimator(new DefaultItemAnimator());


    adapter = new CustomAdapter(data);
    recyclerView.setAdapter(adapter);

    updateArrayList();  


private void updateArrayList() {

    Log.d(TAG, "updateArrayList: setting up for profile fragment");

    DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
    Query query = reference
            .child(getString(R.string.dbname_user_posts))
            .child(FirebaseAuth.getInstance().getCurrentUser().getUid());



    query.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {

            Log.d(TAG, "onChildAdded: explore fragment");
            data.add(dataSnapshot.getValue(Userpost.class));
            adapter.notifyDataSetChanged();
        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {
            Userpost model = dataSnapshot.getValue(Userpost.class);

            final int index = getItemIndex(model);

            data.set(index, model);
            adapter.notifyItemChanged(index);

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }

    });


}


private int getItemIndex(Userpost user) {

    Log.d(TAG, "getItemIndex: setting up for profile fragment");

    int index = -1;

    for (int i = 0; i < data.size(); i++) {
        if (data.get(i).image_path.equals(user.image_path)) {
            index = i;
            break;
        }

    }
    return index;
}

Userpost.java就是这里的模型。

这是logcat：

    java.lang.NullPointerException: Attempt to invoke interface method 'void sahhaj.com.myapp.CustomAdapter$OnItemClickListener.onItemClick(myap.com.myapp.models.Userpost, int)' on a null object reference
                                                                      at sahhaj.com.sahhajapp.CustomAdapter$1.onClick(CustomAdapter.java:112)
                                                                      at android.view.View.performClick(View.java:5721)
                                                                      at android.view.View$PerformClick.run(View.java:22620)

Answer 1

永远不会设置您的OnItemClickListener侦听器属性，因此它是Null。

检查初始化的位置，如果有的话。

Answer 2

这是最好的解决方案 recycler.setonItemselectedliatener（） { Intent（context，mainfragmenr）使用 Startactvity（）： }

Answer 3

更改您的RecyclerView数组适配器类构造函数，如下所示。

public CustomAdapter(ArrayList<Userpost> data, OnItemClickListener listener) {
   this.data = data;
   this.listener = listener;
}

在Fragment中更改RecyclerView数组适配器对象，如下所示进行初始化。

adapter = new CustomAdapter(data, new CustomAdapter.OnItemClickListener() {

            @Override
            public void onItemClick(Userpost userpost, int activityNumber) {

                   // do whatever you want to do                  

                }
            });

就是这样。现在运行代码，您将获得所需的输出。

RecyclerView OnClick转到另一个片段

3 个答案: