我正在尝试在Cloud Firestore中添加文档,但是我需要服务器timestamp
来添加文档。使用正确的timestamp
将文档成功添加到集合中。我正在使用警告对话框添加文档。但是,当我返回到活动应用程序时,由于以下错误而终止:
java.lang.RuntimeException: java.lang.reflect.InvocationTargetException ........ E / AndroidRuntime: 原因: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();
}
}
用于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();
}
});
答案 0 :(得分:2)
代码中的问题是UserLight
类内的时间戳字段的类型与数据库中timestamp
属性的类型不匹配。请参见,在您的UserLight
类中,时间戳记字段的类型为long
,而在数据库中,时间戳记字段的类型基本上为数字Date
或Timestamp
。请注意,两者必须匹配。
由于在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{{1 }},如我在以下帖子中的回答所述: