java.lang.NumberFormatException: null in onBindViewHolder

Question

我正在制作一個聊天應用程序，但是當我單擊發送按鈕時會發生此錯誤.. 請任何人向我解釋 null 的含義以及為什么會發生？ 因為這不是第一次，這對我來說真的很煩人..如果可以的話，請幫助我..

 public class AdapterChat extends RecyclerView.Adapter<AdapterChat.MyHolder> /* this code is second error */
    {
    private static final int MSG_TYPE_LEFT = 0;
    private static final int MSG_TYPE_RIGHT = 1;
    Context context;
    List<Modelchat> chatList;
    String imageUrl;
FirebaseUser fUser;

public AdapterChat(Context context, List<Modelchat> chatList, String imageUrl) {
    this.context = context;
    this.chatList = chatList;
    this.imageUrl = imageUrl;
}

@NonNull
@Override
public MyHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
    if (i == MSG_TYPE_RIGHT) {
        View view = LayoutInflater.from(context).inflate(R.layout.row_chat_right, viewGroup, false);
        return new MyHolder(view);
    } else {
        View view = LayoutInflater.from(context).inflate(R.layout.row_chat_left, viewGroup, false);
        return new MyHolder(view);
    }
}

@Override
public void onBindViewHolder(@NonNull MyHolder myHolder, int i) {
    String message = chatList.get(i).getMessage();
    String timeStamp = chatList.get(i).getTimestamp();

    Calendar cal = Calendar.getInstance(Locale.ENGLISH);
    cal.setTimeInMillis(Long.parseLong(timeStamp)); /* this code is first error*/
    String dataTime = android.text.format.DateFormat.format("dd/MM/yyyy hh:mm aa", cal).toString();

    myHolder.messageTv.setText(message);
    myHolder.timeTv.setText(dataTime);
    try {
        Picasso.get().load(imageUrl).into(myHolder.profileTv);
    } catch (Exception e) {

    }

    if (i == chatList.size()-1) {
        if (chatList.get(i).isSeen()) {
            myHolder.isSeenTv.setText("Seen");
        } else {
            myHolder.isSeenTv.setText("Delivered");
        }
    } else {
        myHolder.isSeenTv.setVisibility(View.GONE);

    }
}

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

@Override
public int getItemViewType(int position) {
    fUser = FirebaseAuth.getInstance().getCurrentUser();
    if (chatList.get(position).getSender().equals(fUser.getUid())) {
        return MSG_TYPE_RIGHT;
    } else {
        return MSG_TYPE_LEFT;
    }
}

class MyHolder extends RecyclerView.ViewHolder {

    ImageView profileTv;
    TextView messageTv, timeTv, isSeenTv;


    public MyHolder(@NonNull View itemView) {
        super(itemView);

        profileTv = itemView.findViewById(R.id.profileTv);
        messageTv = itemView.findViewById(R.id.messageTv);
        timeTv = itemView.findViewById(R.id.timeTv);
        isSeenTv = itemView.findViewById(R.id.isSeenTv);

    }
}
}

錯誤信息

 java.lang.NumberFormatException: null

    at cm.example.learno.SocialApp.adapters.AdapterChat.onBindViewHolder(AdapterChat.java:56)
    at com.example.learno.SocialApp.adapters.AdapterChat.onBindViewHolder(AdapterChat.java:23)

我在錯誤代碼旁邊發表了評論

Answer 1

嘗試改變

String timeStamp = chatList.get(i).getTimestamp();

至

String timeStamp = chatList.get(myHolder.getAdapterPosition()).getTimestamp();

您正在嘗試將 null 值 timeStamp 解析為

cal.setTimeInMillis(Long.parseLong(timeStamp));

至於null是什么，請花點時間研究一下。 你可以從這里開始

Answer 2

如果要同時格式化日期和時間，請使用 DateTimeFormatter 而不是 DateFormat。 另一種解決方法是從格式化程序中刪除時間，例如dd/MM/yyyy