在 Firestore 中获取服务器时间戳时出错

Question

我正在尝试在 Cloud Firestore 中添加文档，但我需要服务器 timestamp 来添加文档。使用正确的timestamp 将文档成功添加到集合中。我正在添加带有警报对话框的文档。但是当我返回我的活动时，应用程序终止并出现以下错误：

java.lang.RuntimeException: java.lang.reflect.InvocationTargetException ........ E/AndroidRuntime: 引起：java.lang.NullPointerException：尝试调用虚拟 方法'java.util.Date com.google.firebase.Timestamp.toDate()' 空对象引用 在 com.sasam.virtuallibrary.Models.UserLight.setTimestamp(UserLight.java:103)

为了显示文档，我正在使用以下查询

Query query= FirebaseFirestore.getInstance()
                .collection("Users")
                .document(user.getUid())
                .collection("friends")
                .orderBy("timestamp", Query.Direction.DESCENDING);

我的课来了

public class UserLight{

    protected String name;
    protected String email;
    protected String uid;
    protected Float rating;
    protected String photoUrl;
    protected long timestamp;


    public UserLight(){

    }

    //other getters and setters

    @Exclude
    public long getTimestampLong(){
        return timestamp;
    }
    public FieldValue getTimestamp() {
        return  FieldValue.serverTimestamp();
    }

    public void setTimestamp(Timestamp timestamp) {
        this.timestamp = timestamp.toDate().getTime();
    }

}

处理来自查询的快照的代码

Query query= FirebaseFirestore.getInstance()
                .collection("Users")
                .document(user.getUid())
                .collection("friends")
                .orderBy("timestamp", Query.Direction.DESCENDING);

        PagedList.Config config = new PagedList.Config.Builder()
                .setEnablePlaceholders(false)
                .setPrefetchDistance(5)
                .setPageSize(10)
                .build();

        FirestorePagingOptions<UserLight> options = new FirestorePagingOptions.Builder<UserLight>()
                .setLifecycleOwner(this)
                .setQuery(query, config, UserLight.class)
                .build();


        mAdapter = new FirestorePagingAdapter<UserLight, ItemFriendViewHolder>(options) {
            @NonNull
            @Override
            public ItemFriendViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
                return new ItemFriendViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.rc_item_friend, parent, false));
            }

            @Override
            protected void onBindViewHolder(@NonNull ItemFriendViewHolder holder, int position, @NonNull final UserLight userLight) {


                holder.txtName.setText(userLight.getName());
                GlideApp.with(holder.context).load(userLight.getPhotoUrl()).into(holder.avata);

                holder.cardView.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        Intent intent=new Intent(FriendListActivity.this,FinalChatActivity.class);
                        intent.putExtra("Friend", (Serializable) userLight);
                        startActivity(intent);
                    }
                });

            }

            @Override
            protected void onLoadingStateChanged(@NonNull LoadingState state) {
                switch (state) {
                    case LOADING_INITIAL:
                    case LOADING_MORE:
                        // Do your loading animation
                        mSwipeRefreshLayout.setRefreshing(true);
                        break;

                    case LOADED:
                        // Stop Animation
                        mSwipeRefreshLayout.setRefreshing(false);
                        break;

                    case FINISHED:
                        //Reached end of Data set
                        mSwipeRefreshLayout.setRefreshing(false);
                        break;

                    case ERROR:
                        retry();
                        break;
                }
            }


            @Override
            protected void onError(@NonNull Exception e) {
                super.onError(e);
                mSwipeRefreshLayout.setRefreshing(false);
            }

        };

        recyclerView.setAdapter(mAdapter);

        mSwipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                mAdapter.refresh();
            }
        });

插入后的文档

Answer 1

代码中的问题是UserLight 类中时间戳字段的类型与数据库中timestamp 属性的类型不匹配。看，在您的UserLight 类中，时间戳字段的类型为long，它基本上是一个数字，而数据库中的类型为Date 或Timestamp。请注意，两者必须匹配。

因为在 Cloud Firestore 中保存日期的正确方法是使用 Date 或 Timestamp 类，要解决此问题，只需将模型类中时间戳字段的类型更改为 Date，如在我在以下帖子中的回答：

• ServerTimestamp is always null on Firebase Firestore