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。文档已成功添加到集合中且 timestamp 正确。我正在添加带有警告对话框的文档。但是，当我返回我的 activity 应用程序时，它因以下错误而终止：

java.lang.RuntimeException: java.lang.reflect.InvocationTargetException ........ E/AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.Date com.google.firebase.Timestamp.toDate()' on a null object reference at 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class在这里

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();
    }

}

处理查询快照的代码

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();
            }
        });

文档插入后

Answer 1

您的代码中的问题是 UserLight class 中的时间戳字段类型与 timestamp 属性中的类型不匹配在数据库中。看，在您的 UserLight class 中，时间戳字段是 long 类型，它基本上是一个数字，而在数据库中是 Date 或 Timestamp 类型。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 class，要解决这个问题，只需更改模型中时间戳字段的类型class 为 Date，正如我在以下 post:

的回答中所解释的

在 Firestore 中获取服务器时间戳时出错

Error in getting server timestamp in Firestore

java

android

firebase

firebaseui

google-cloud-firestore