Question

我将两个Firestore查询分配给LiveData对象。这些查询中的每一个都返回到不同的对象类：User和Book。我需要将它们合并在一起并应用转换，这样我就可以创建一个组合了两组数据（查询）的LinkedHashmap。为了做到这一点，我使用了MediatorLive数据，并且能够使用QuerySnapshot作为返回类型合并我使用的两个不同的类。

我遇到的问题是当我输出MediatorLiveData对象的结果时，我得到结果两次并且复合。此外，第一次结果为Book类返回null，第二次结果为User类返回null。

我错过了什么？

这里简化了我的代码：

这些是我的Firestore查询和LiveData分配：

    //getUsers query using FirebaseQueryLiveData class
    private Query getUsersQuery() {
        FirebaseAuth mAuth = FirebaseAuth.getInstance();

        adminID = mAuth.getUid();
        query = FirebaseFirestore.getInstance().collection("admins")
                .document(adminID)
                .collection("users")
        return query;
    }

    private FirebaseQueryLiveData usersLiveData = new FirebaseQueryLiveData(getUsersQuery());


    //getBooks query using FirebaseQueryLiveData class
    private Query getBooksQuery () {
        FirebaseGroupID firebaseGroupID = new FirebaseGroupID(getApplication());
        groupID = firebaseGroupID.getGroupID();
        query = FirebaseFirestore.getInstance().collection("books")
                .whereEqualTo("groupID", groupID)      
        return query;
    }

    private FirebaseQueryLiveData booksLiveData = new FirebaseQueryLiveData(getBooksQuery());

下面是我的MediatorLiveData和关联get方法：

    //MediatorLiveData merge two LiveData QuerySnapshot streams
    private MediatorLiveData<QuerySnapshot> usersBooksLiveDataMerger() {
        final MediatorLiveData<QuerySnapshot> mediatorLiveData = new MediatorLiveData<>();
        mediatorLiveData.addSource(usersLiveData, new Observer<QuerySnapshot>() {
            @Override
            public void onChanged(@Nullable QuerySnapshot querySnapshot) {
                mediatorLiveData.setValue(querySnapshot);
            }
        });
        mediatorLiveData.addSource(booksLiveData, new Observer<QuerySnapshot>() {
            @Override
            public void onChanged(@Nullable QuerySnapshot querySnapshot) {
                mediatorLiveData.setValue(querySnapshot);
            }
        });
        return mediatorLiveData;
    }

    //get method to get our merged LiveData streams
    public MediatorLiveData<QuerySnapshot> getUsersBooksLiveDataMerger() {
        return usersBooksLiveDataMerger();
    }

在MainActivity中，这是我的观察者：

    //Main Activity observer
    mainViewModel.getUsersBooksLiveDataMerger().observe(this, new Observer<QuerySnapshot>() {
            @Override
            public void onChanged(@Nullable QuerySnapshot querySnapshot) {
                if (querySnapshot != null) {
                    List<Book> books;
                    List<User> users;
                    books = querySnapshot.toObjects(Book.class);
                    users = querySnapshot.toObjects(User.class);
                    Log.d(TAG, "OBSERVE MERGE users: " + users);
                    Log.d(TAG, "OBSERVE MERGE books: " + books);
                }
            }
        });

最后，这是我得到的合并的输出：

MainActivity：观察MERGE用户：[用户{用户ID =＆＃39; OtlmIQxeLkvNYExsxjg4＆＃39 ;,的userName =＆＃39;莉莎＆＃39 ;, lastDisplayedBookID =＆＃39;无＆＃39 ;, isAllBooks =假，dateCreated会=星期三5月23日11时27分二十秒PDT 2018，dateModified =星期三5月23日11时27分二十秒PDT 2018，allBookID =＆＃39; akuGpq7aMB85J9QMtsBi＆＃39 ;,组ID =＆＃39; S0Ql3hnHmXACUqeGW04n＆＃39;}]

MainActivity：OBSERVE MERGE书籍：[预订{bookAssigned = false，bookName =＆＃39; null＆＃39;，bookType =＆＃39; null＆＃39;，assignedTo =＆＃39; null＆＃39;，bookID =＆＃39;空＆＃39 ;,组ID =＆＃39; S0Ql3hnHmXACUqeGW04n＆＃39 ;,用户ID =＆＃39; OtlmIQxeLkvNYExsxjg4＆＃39 ;, dateCreated会=星期三5月23日11时27分20秒PDT 2018，lastAssignedDate = NULL，bookNum = 0}]

MainActivity：观察MERGE用户：[用户{用户ID =＆＃39; OtlmIQxeLkvNYExsxjg4＆＃39 ;,的userName =＆＃39;空＆＃39 ;, lastDisplayedBookID =＆＃39;空＆＃39 ;, isAllBooks =假，dateCreated会= NULL，dateModified = NULL，allBookID =＆＃39;空＆＃39 ;,组ID =＆＃39; S0Ql3hnHmXACUqeGW04n＆＃39;}，用户{用户ID =＆＃39; OtlmIQxeLkvNYExsxjg4＆＃39 ;,的userName =＆＃39;空＆＃39;，lastDisplayedBookID =＆＃39; null＆＃39;，isAllBooks = false，dateCreated = Wed May 23 11:27:20 PDT 2018，dateModified = null，allBookID =＆＃39; null＆＃39;，groupID =＆＃39; S0Ql3hnHmXACUqeGW04n＆＃39;}]

MainActivity：OBSERVE MERGE书籍：[预订{bookAssigned = false，bookName =＆＃39;所有图书＆＃39;，bookType =＆＃39; NA＆＃39;，assignedTo =＆＃39; Lisa＆＃39;， bookID =＆＃39; akuGpq7aMB85J9QMtsBi＆＃39;，groupID =＆＃39; S0Ql3hnHmXACUqeGW04n＆＃39;，userID =＆＃39; OtlmIQxeLkvNYExsxjg4＆＃39;，dateCreated = null，lastAssignedDate = null，bookNum = 0}，预订{bookAssigned =是的，bookName =＆＃39;饥饿游戏＆＃39;，bookType =＆＃39; Soft Cover＆＃39;，assignedTo =＆＃39; Lisa＆＃39;，bookID =＆＃39; 2D9C293DCB4469904532FF3FD81B3E7B＆＃39;，groupID = ＆＃39; S0Ql3hnHmXACUqeGW04n＆＃39 ;,用户ID =＆＃39; OtlmIQxeLkvNYExsxjg4＆＃39 ;, dateCreated会=星期三5月23日11点27分20秒PDT 2018，lastAssignedDate =星期三5月23日11点27分20秒PDT 2018，bookNum = 1} ]

正如您所看到的，结果似乎复合但具有空值。

对此的任何帮助将不胜感激！

使用MediatorLiveData合并到LiveData（Firestore）QuerySnapshot流产生了奇怪的结果

0 个答案: