android - 如何在for循环内同步执行firebase函数？

Question

我在 for 循环中从 firebase 数据库中检索数据，但问题是 firebase 函数不是同步执行的，我知道 firebase 函数是异步的。有什么解决办法吗？

代码:-

registrationReference.child(userId).child("generated_links").addListenerForSingleValueEvent(new ValueEventListener()
        {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                peopleModelList.clear();

                for(DataSnapshot snapshot : dataSnapshot.getChildren())
                {
                    peopleModel = new PeopleModel();

                    peopleHashMap =(HashMap)snapshot.getValue();

                    peopleModel.setChatWith((String)peopleHashMap.get("chatWith"));
                    peopleModel.setNickname((String)peopleHashMap.get("nickname"));
                    peopleModel.setChatRoom(snapshot.getKey());

                    Log.d("kkkk","1st");

                    if(peopleModel.getChatWith()!=null && !("".equals(peopleModel.getChatWith())))
                    {
                        registrationReference.child(peopleModel.getChatWith()).addListenerForSingleValueEvent(new ValueEventListener() {
                            @Override
                            public void onDataChange(DataSnapshot dataSnapshot) {
                                peopleModel.setRefresh_token((String)dataSnapshot.child("refresh_token").getValue());
                                peopleModelList.add(peopleModel);
                                Log.d("kkkk","2nd");
                            }

                            @Override
                            public void onCancelled(DatabaseError databaseError) {

                            }
                        });
                    }
                    Log.d("kkkk","3rd");

                }
                iCallBackPeople.peopleAct(peopleModelList);
            }

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

输出:-

1st
3rd
2nd

但我想要这样的输出

1st
2nd
3rd

注意:- 我搜索过，但从未找到任何解决方案!

How to get data from Firebase Database in a loop?

Firebase addListenerForSingleValueEvent excute later in loop

我试过这个但对我不起作用，它是用最后一项填充我的列表!

public void listOfUsers(final ICallBackPeople iCallBackPeople) {
        count=0;
        //peopleModelList = new ArrayList<>();
        sortedMap = new TreeMap<>();
       // peopleModelList = new ArrayList<PeopleModel>(sortedMap.values());
        registrationReference.child(userId).child("generated_links").addListenerForSingleValueEvent(new ValueEventListener()
        {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
             //   peopleModelList.clear();

                for(DataSnapshot snapshot : dataSnapshot.getChildren())
                {
                    peopleModel = new PeopleModel();

                    peopleHashMap =(HashMap)snapshot.getValue();

                    peopleModel.setChatWith((String)peopleHashMap.get("chatWith"));
                    peopleModel.setNickname((String)peopleHashMap.get("nickname"));
                    peopleModel.setChatRoom(snapshot.getKey());

                    //Object chatRoom = snapshot.getKey();
                    Log.d("kkkk","1st");

                    if(peopleModel.getChatWith()!=null && !("".equals(peopleModel.getChatWith())))
                    {

                        addItem(count,iCallBackPeople);
                        count++;
                    }
                    Log.d("kkkk","3rd");

                }
                Log.d("kkkk","end");
                //iCallBackPeople.peopleAct(peopleModelList);
            }

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

    private void addItem(final int index, final ICallBackPeople iCallBackPeople) {
        registrationReference.child(peopleModel.getChatWith()).addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                peopleModel.setRefresh_token((String)dataSnapshot.child("refresh_token").getValue());
                Log.d("kkkk","2nd");
                sortedMap.put(index, peopleModel);
                // sortedMap will sort your list by key (in this case, key is integer)


                 if(sortedMap.size()==2)
                 {
                     peopleModelList = new ArrayList<PeopleModel>(sortedMap.values());
                     iCallBackPeople.peopleAct(peopleModelList);
                 }

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }

我试过了，但没有得到所有项目，只得到快照中最后一个项目的列表

public void listOfUsers(final ICallBackPeople iCallBackPeople) {

        peopleModelList = new ArrayList<>();

        registrationReference.child(userId).child("generated_links").addListenerForSingleValueEvent(new ValueEventListener()
        {
            PeopleModel peopleModel;
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                peopleModelList.clear();

                for(final DataSnapshot snapshot : dataSnapshot.getChildren())
                {
                    peopleModel = new PeopleModel();

                    peopleHashMap =(HashMap)snapshot.getValue();

                    peopleModel.setChatWith((String)peopleHashMap.get("chatWith"));
                    peopleModel.setNickname((String)peopleHashMap.get("nickname"));
                    peopleModel.setChatRoom(snapshot.getKey());


                    if(peopleModel.getChatWith()!=null && !("".equals(peopleModel.getChatWith())))
                    {
                        getToken(new CallBackGetToken() {
                            @Override
                            public void token(String token) {
                                peopleModel.setRefresh_token(token);
                                Toast.makeText(context, token, Toast.LENGTH_SHORT).show();
                                peopleModelList.add(peopleModel);

                                //here i am checking my peopleModelList size is equal or not to snapshot
                                if(peopleModelList.size()==2)
                                    iCallBackPeople.peopleAct(peopleModelList);
                            }
                        },peopleModel);
                    }
                }
            }

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

    private void getToken(final CallBackGetToken callBackGetToken ,PeopleModel peopleModel) {
        registrationReference.child(peopleModel.getChatWith()).addListenerForSingleValueEvent(new ValueEventListener() {
                            @Override
                            public void onDataChange(DataSnapshot dataSnapshot) {
                                callBackGetToken.token((String)dataSnapshot.child("refresh_token").getValue());
                            }

                            @Override
                            public void onCancelled(DatabaseError databaseError) {

                            }
                        });
    }

Answer 1

我认为您应该通过一个接口(interface)(创建一个接口(interface)并在此类中实现)。接口(interface)内的方法应该有一个字符串作为参数(它将接收您的 peopleModel.getChatWith() )。

在您的 if(peopleModel.getChatWith()!=null && !("".equals(peopleModel.getChatWith()))) 中，您应该请求您的界面。

我认为这是您异步问题的解决方案。