如何同步从 Firebase 中的表中获取所有行？

Question

考虑下面的sn-p代码：

public ArrayList<GenericModel> getList(GenericModel model) {
    ValueEventListener postListener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            ArrayList<GenericModel> genericModels = new ArrayList<>();

            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                GenericModel genericModel = postSnapshot.getValue(model.getClass());
                genericModels.add(genericModel);
            }
            Collections.sort(genericModels, (o1, o2) -> o1.getDate().compareTo(o2.getDate()));

            return genericModels;
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            return null;
        }
    };
    mDatabase.child(model.getTableName()).child(mUser.getUid()).addListenerForSingleValueEvent(postListener);
}

目前这段代码不起作用，我只能通过回调来解决这个问题。我不希望那样。我想要一个返回 ArrayList 的方法。我怎么能重写这个？使用 Kotlin 也是一种选择。

Answer 1

public Task<ArrayList<GenericModel>> getList(GenericModel model) {
    if (!mIsInitialized) {
        initialize();
    }

    final TaskCompletionSource<ArrayList<GenericModel>> tcs = new TaskCompletionSource<>();

    if (mIsInitialized) {
        ValueEventListener postListener = new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                ArrayList<GenericModel> genericModels = new ArrayList<>();

                for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                    GenericModel genericModel = postSnapshot.getValue(model.getClass());
                    genericModels.add(genericModel);
                }
                Collections.sort(genericModels, (o1, o2) -> o1.getDate().compareTo(o2.getDate()));

                tcs.setResult(genericModels);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
                tcs.setResult(null);
            }
        };

        mDatabase.child(model.getTableName()).child(mUser.getUid()).addListenerForSingleValueEvent(postListener);

    }
    return tcs.getTask();
}

这里是调用方法：(Kotlin, with co-routines)

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    doAsync {
        val task = FirebaseManager.getInstance().getList(FixedCosts())
        task.addOnCompleteListener {
            uiThread {
                if (task.result != null) {
                    //show the result in UI 
                }
          }
      }
}

Answer 2

在这段代码中，我正在检索该节点中所有可用的行：

//全局变量\ ArrayList arrayListEventName = new ArrayList();

public ArrayList<String or Pojo>getEventNames() {
        progressDialog();
        //----Shared Preference----\\
        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
        String emailId = prefs.getString(StaticValues.PREF_EMAIL, "name@provider,com");
        emailId = emailId.replace(".", ",");
        //--------------\\

        database = FirebaseDatabase.getInstance(); // Database Instance \\
        DatabaseReference databaseReference_users = database.getReference("admin").child(emailId)
                .child("eventsCreated");
        databaseReference_users.addValueEventListener(new com.google.firebase.database.ValueEventListener() {

            @Override
            public void onDataChange(final com.google.firebase.database.DataSnapshot dataSnapshot) {
                arrayListEventName.clear();

                for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                    String eventName = (String) postSnapshot.child("eventName").getValue(String.class).toLowerCase();
//                    if(eventName.equals(eventName2)){
//
//                    }
                    arrayListEventName.add(eventName);
                }

                dismissDialog();
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
            }
        });

返回数组列表事件名称；

    }

截图：