如何知道firebase ChildEventListener是否发现孩子？ [机器人] [英] how to know if firebase ChildEventListener found child ? [android]

问题描述

所以我试图通过他们的电子邮件获取用户密钥，问题是，我不知道我的代码里面，如果查询实际上发现的东西或没有..所以我假设，如果我在onchildadded，查询是成功的，一个孩子已被发现，所以我会通过钥匙到另一个活动，并停止当前的活动，但是当我运行应用程序的整个代码得到执行..我觉得我的方式有点不对，但我没有找到任何方式知道如果查询是sucsessful或孩子被发现....如果您有任何想法请求帮助...

  public void searchemail（String email）{
 
 Firebase ref = new Firebase（https：//< myfirebase> .firebaseio.com / users）; 
 Query queryRef = ref.orderByChild（Email）。equalTo（email）; 
 
 $ b ChildEventListener listener = new ChildEventListener（）{
 $ b @Override 
 public void onChildAdded（DataSnapshot dataSnapshot，String s）{
 
 userkey = dataSnapshot.getKey（）; 
 homeintent.putExtra（key，userkey）; 
 startActivity（homeintent）; 
 finish（）; 
 return; 
 //我想让代码停在这里
 
}} 
 queryRef.addChildEventListener（listener）; 
 
 Toast Toast = Toast.makeText（这个找不到电子邮件，Toast.LENGTH_SHORT）; / /我假设如果我在这里然后没有找到孩子，但总是得到执行之前，开始活动
} 
  

输出：
如果找到电子邮件 - > toast将显示，然后家庭活动将开始...
如果没有找到电子邮件 - >只有烤面包将显示..

<当发生相关的事件时， ChildEventListener 的方法被调用。 所以 onChildAdded（）在添加子项时将被称为。出于这个原因，如果小孩存在，你不能轻易使用 ChildEventListener 来检测 。

检测孩子是否存在的最简单方法是使用 ValueEventListener ：

  public void searchemail（String email）{
 
 Firebase ref = new Firebase（https：//< myfirebase> .firebaseio.com / users）; 
 Query queryRef = ref.orderByChild（Email）。equalTo（email）; 
 
 $ b ValueEventListener listener = new ValueEventListener（）{
 $ b @Override 
 public void onDataChanged（DataSnapshot snapshot）{
 if（snapshot。 exists（））{
 for（DataSnapshot child：snapshot.getChildren（））{
 homeintent.putExtra（key，child.getKey（））; 
 startActivity（homeintent）; 
 break; //退出for循环，我们只想要一个匹配
 
 $ b $ else $ $ $ $ toast.makeText Toast.makeText（这个找不到电子邮件，Toast.LENGTH_SHORT） ; 
} 
} 
}; 
 queryRef.addValueEventListener（listener）; 
} 
  

so I'm trying to get users key by their email and the problem is that I dont know inside my code if the query actually found something or not .. so I'm assuming if I'm inside onchildadded that the query is successful and a child has been found so I will pass the key to another activity and stop current activity but when I run the app the whole code get executed .. I feel my way is kinda wrong but I didn't find any way to know if the query is sucsessful or a child is found .... if you have any idea pleas help ...

  public void searchemail(String email){

  Firebase ref = new Firebase("https://<myfirebase>.firebaseio.com/users");
    Query queryRef = ref.orderByChild("Email").equalTo(email);


     ChildEventListener listener = new ChildEventListener() {

        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {

            userkey = dataSnapshot.getKey();
              homeintent.putExtra("key", userkey);
               startActivity(homeintent);
               finish();
               return; 
                 // I want code to stop here 

        }}
    queryRef.addChildEventListener(listener);

      Toast toast = Toast.makeText(this, "email not found", Toast.LENGTH_SHORT); // Im assuming if Im here then no child is found but this always get executed before startactivity  
   }

OUTPUT : if email found -> toast will show then home activity will start... if email not found -> only toast will show..

解决方案

The methods of a ChildEventListener get called when the relevant event happened. So onChildAdded() will be called when a child has been added. For this reason you cannot easily use a ChildEventListener to detect if a child exists.

The easiest way to detect if a child exists, is to use a ValueEventListener:

public void searchemail(String email){

  Firebase ref = new Firebase("https://<myfirebase>.firebaseio.com/users");
  Query queryRef = ref.orderByChild("Email").equalTo(email);


   ValueEventListener listener = new ValueEventListener() {

     @Override
     public void onDataChanged(DataSnapshot snapshot) {
       if (snapshot.exists()) {
         for (DataSnapshot child: snapshot.getChildren()) {
           homeintent.putExtra("key", child.getKey());
           startActivity(homeintent);
           break; // exit for loop, we only want one match
         }
       }
       else {
         Toast toast = Toast.makeText(this, "email not found", Toast.LENGTH_SHORT);
       }
     }
   };
   queryRef.addValueEventListener(listener);
}

这篇关于如何知道firebase ChildEventListener是否发现孩子？ [机器人]的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！