java - 如何解决 Android Studio Firebase 问题？

Question

这个问题已经有答案了:

Problems with Firestore connections executing threads (3 个回答)

已关闭 3 年前。

我正在尝试从 Firebase 获取数据到 bilgiler 变量。但我总是出错。我该如何解决这个问题？

Map<String, String> bilgiler = new HashMap<>();

db.collection("tarihBilgi")
                .get()
                .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                        if (task.isSuccessful()) {
                            for (QueryDocumentSnapshot document : Objects.requireNonNull(task.getResult())) {
                                //Log.d("TAG", document.getId() + " => " + document.getData());
                                bilgiler.put("asdf", document.getData().toString());
                            }
                        } else {
                            Log.w("TAG", "Error getting documents.", task.getException());
                        }
                    }
                });
        Log.i("asdfads",(bilgiler.get("asdf")));

Answer 1

数据是从 Firebase 异步加载的。现在你的Log.i("asdfads",(bilgiler.get("asdf")));在bilgiler.put("asdf", document.getData().toString())之前运行运行，这解释了为什么您看不到数据库中的值。

任何需要数据库数据的代码都需要位于 onComplete 内方法，或者从那里调用。所以:

db.collection("tarihBilgi")
    .get()
    .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
        @Override
        public void onComplete(@NonNull Task<QuerySnapshot> task) {
            if (task.isSuccessful()) {
                for (QueryDocumentSnapshot document : Objects.requireNonNull(task.getResult())) {
                    bilgiler.put("asdf", document.getData().toString());
                    Log.i("asdfads",(bilgiler.get("asdf")));
                }
            } else {
                Log.w("TAG", "Error getting documents.", task.getException());
            }
        }
    });

另请参阅:

• How to check a certain data already exists in firestore or not
• User login in Firebase
• How to return a DocumentSnapShot as a result of a method?
• Wait until Firestore data is retrieved to launch an activity
• Problems with Firestore connections executing threads