Firebase侦听器代码未被触发 [英] Firebase Listener code not being triggered

问题描述

我有一个从Activity类调用的RideList类，它从Firebase数据库中检索数据。但是，当我调试我的程序时，我的addValueEventListener中的代码是永远不会到达的。

  public class RideList {
 private的ArrayList<平顺> listofRides; 
公开的Firebase myFirebase =新的Firebase（https://luminous-torch-1510.firebaseio.com/rides）; 
上下文上下文; 
 public RideList（Context context）{
 this.context = context; 
 this.listofRides = new ArrayList< Ride>（）; 
} 
 
 public ArrayList< Ride> getRides（）{
 Firebase.setAndroidContext（context）; 
 //附加一个监听器来读取我们游乐设施中的数据参考
 Query queryRef = myFirebase.orderByChild（timePosted）; 
 try {
 queryRef.addValueEventListener（new ValueEventListener（）{
 @Override 
 public void onDataChange（DataSnapshot snapshot）{
 System.out.println（There are + snapshot.getChildrenCount（）+rides）; 
 for（DataSnapshot postSnapshot：snapshot.getChildren（））{
字符串rideString = postSnapshot.getValue（）。toString（）; 
 String [] rideA = rideString.split（）; 
字符串值; 
（int i = 0; i< rideA.length  -  1; i ++）{
 rideA [i ] = rideA [i] .substring（rideA [i] .indexOf（=）+ 1）; 
 rideA [i] = rideA [i] .substring（0，rideA [i] .indexOf（ ，））; 
} 
 rideA [rideA.length  -  1] = rideA [rideA.length  -  1] .substring（rideA [rideA.length  -  1] .indexOf（=）+ 1）; $ b $ rideA [rideA.length  -  1] = rideA [rideA.length  -  1] .substring（0，rideA [rideA.length  -  1] .indexOf（}））; 
 
 
 double numOfPassengers = Double.valueOf（rideA [6]）; 
双重票价= Double.valueOf（rideA [4]）; 
 double distance = Double.valueOf（rideA [3]）; 
 String origin = rideA [7]; 
 String destination = rideA [2]; 
 double maxPassengers = Double.valueOf（rideA [5]）; 
字符串departTime = rideA [1]; 
 String arrivalTime = rideA [0]; 
 String timePosted = rideA [8]; 
 String title = rideA [9]; 
 String type1 = rideA [10]; 
布尔类型; 
 if（type1.equals（offer））
 type = false; 
 else 
 type = true; 
 
 
乘车=新乘车（numOfPassengers，票价，距离，出发地，目的地，maxPassengers，departureTime，arrivalTime，
 timePosted，标题，类型）; 
 listofRides.add（ride）; 
 
 
 $ b @Override 
 public void onCancelled（FirebaseError firebaseError）{
 System.out.println（The read failed：+ firebaseError .getMessage（））; 
} 
}）; 
 Thread.sleep（2000）; 
} catch（InterruptedException e）{
 return null; 
} 
 return listofRides; 
 
 
 $ b $ / code 
 $ b 
这段代码是从一个Activity类的OnCreate函数。任何想法为什么听众代码从来没有被输入/执行？
 
 
编辑：下面是这个函数在activity类中被调用的代码。
  list =（ListView）findViewById（R.id.showrides_listView）; 
 Firebase.setAndroidContext（this）; 
 RideList rl = new RideList（this）; 
 ArrayList arrayList = rl.getRides（）; 
 //适配器：需要三个参数：布局的上下文ID（它将显示数据的位置）
 //包含数据的数组$ b $ ArrayAdapter适配器= new ArrayAdapter< Ride>（getApplicationContext（），android.R.layout.simple_spinner_item，arrayList）{
 @Override 
 public View getView（int position，View convertView，ViewGroup parent）{
 View view = super.getView（position，convertView，parent）; 
 TextView text =（TextView）view.findViewById（android.R.id.text1）; 
 text.setTextColor（Color.BLACK）; 
返回视图; 
} 
}; 
 
 //在这里，您将ListView中的数据设置为
 list.setAdapter（adapter）; 
 adapter.notifyDataSetChanged（）; 
 
 FloatingActionButton myFab =（FloatingActionButton）findViewById（R.id.showrides_fab）; 
 myFab.setOnClickListener（new View.OnClickListener（）{
 public void onClick（View v）{
 startCreateRideActivity（）; 
} 
}）; 
  
 
 
解决方案
您的数据正在异步加载同步）来自Firebase。把 Thread.sleep（）放在那里是不会改变这个事实的。
 
 
 
如果您添加一些日志语句会发生： 
 
 
  public ArrayList< Ride> getRides（）{
 Query queryRef = myFirebase.orderByChild（timePosted）; 
尝试{
 System.out.println（Adding listener）; 
 queryRef.addValueEventListener（new ValueEventListener（）{
 public void onDataChange（DataSnapshot snapshot）{
 //此代码被异步调用
 System.out.println（ Firebase）; 
} 
 public void onCancelled（FirebaseError firebaseError）{
} 
}）; 
 System.out.println（开始睡眠）; 
 Thread.sleep（2000）; 
} catch（InterruptedException e）{
 return null; 
} 
 System.out.println（返回游乐设施）; 
 return listofRides; 
 
 
 
 
 
 
输出可能是：
 
 
 
 
添加监听程序
 
 
 
开始睡眠 
 
 
返回游乐设施
 
 
 
从Firebase获取数据
 
 
您试图使异步进程同步，这是头痛和糟糕的用户体验的秘诀。而不是在这里写一个解决方案，我会链接到一个答案，我写了15分钟前相同的问题：检索ArrayList< Object>来自FireBase内部类 
 
I have a RideList class that is called from an Activity class that retrieves data from a Firebase database. However, when I debug my program the code within my addValueEventListener is never being reached.
public class RideList {
        private ArrayList<Ride> listofRides;
        public Firebase myFirebase = new Firebase("https://luminous-torch-1510.firebaseio.com/rides");
        Context context;
    public RideList(Context context) {
        this.context = context;
        this.listofRides = new ArrayList <Ride>();
    }

    public ArrayList<Ride> getRides() {
        Firebase.setAndroidContext(context);
        // Attach an listener to read the data at our rides reference
        Query queryRef = myFirebase.orderByChild("timePosted");
        try {
            queryRef.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot snapshot) {
                    System.out.println("There are " + snapshot.getChildrenCount() + " rides");
                    for (DataSnapshot postSnapshot : snapshot.getChildren()) {
                        String rideString = postSnapshot.getValue().toString();
                        String[] rideA = rideString.split(" ");
                        String value;
                        for (int i = 0; i < rideA.length - 1; i++) {
                            rideA[i] = rideA[i].substring(rideA[i].indexOf("=") + 1);
                            rideA[i] = rideA[i].substring(0, rideA[i].indexOf(","));
                        }
                        rideA[rideA.length - 1] = rideA[rideA.length - 1].substring(rideA[rideA.length - 1].indexOf("=") + 1);
                        rideA[rideA.length - 1] = rideA[rideA.length - 1].substring(0, rideA[rideA.length - 1].indexOf("}"));


                        double numOfPassengers = Double.valueOf(rideA[6]);
                        double fare = Double.valueOf(rideA[4]);
                        double distance = Double.valueOf(rideA[3]);
                        String origin = rideA[7];
                        String destination = rideA[2];
                        double maxPassengers = Double.valueOf(rideA[5]);
                        String departTime = rideA[1];
                        String arrivalTime = rideA[0];
                        String timePosted = rideA[8];
                        String title = rideA[9];
                        String type1 = rideA[10];
                        boolean type;
                        if (type1.equals("offer"))
                            type = false;
                        else
                            type = true;


                        Ride ride = new Ride(numOfPassengers, fare, distance, origin, destination, maxPassengers, departTime, arrivalTime,
                                timePosted, title, type);
                        listofRides.add(ride);
                    }
                }

                @Override
                public void onCancelled(FirebaseError firebaseError) {
                    System.out.println("The read failed: " + firebaseError.getMessage());
                }
            });
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            return null;
        }
        return listofRides;
    }

    }
This code is being called from an OnCreate function of an Activity class. Any idea on why the listener code is never being entered/executed?

Edit: Here is the code on how this function is being called in the activity class.
list = (ListView) findViewById(R.id.showrides_listView);
Firebase.setAndroidContext(this);
RideList rl = new RideList(this);
ArrayList arrayList = rl.getRides();
// Adapter: You need three parameters 'the context, id of the layout (it will be where the data is shown),
// and the array that contains the data
ArrayAdapter adapter = new ArrayAdapter<Ride>(getApplicationContext(), android.R.layout.simple_spinner_item, arrayList){
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View view = super.getView(position, convertView, parent);
        TextView text = (TextView) view.findViewById(android.R.id.text1);
        text.setTextColor(Color.BLACK);
        return view;
    }
};

// Here, you set the data in your ListView
list.setAdapter(adapter);
adapter.notifyDataSetChanged();

FloatingActionButton myFab = (FloatingActionButton)  findViewById(R.id.showrides_fab);
myFab.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
       startCreateRideActivity();
    }
});

解决方案
Your data is being loaded asynchronously (and after that continuously synchronized) from Firebase. Putting a Thread.sleep() in there is not going to change that fact.

You can easily see what happens if you add a few log statements:
public ArrayList<Ride> getRides() {
    Query queryRef = myFirebase.orderByChild("timePosted");
    try {
        System.out.println("Adding listener");
        queryRef.addValueEventListener(new ValueEventListener() {
            public void onDataChange(DataSnapshot snapshot) {
                // THIS CODE IS CALLED ASYNCHRONOUSLY
                System.out.println("Got data from Firebase");
            }
            public void onCancelled(FirebaseError firebaseError) {
            }
        });
        System.out.println("Starting sleep");
        Thread.sleep(2000);
    } catch (InterruptedException e) {
        return null;
    }
    System.out.println("Returning rides");
    return listofRides;
}
The output is likely:

  
Adding listener
  
  
Starting sleep
  
  
Returning rides
  
  
Got data from Firebase
You're trying to make an asynchronous process synchronous, which is a recipe for headaches and a bad user experience. Instead of writing up a solution here, I'll link to an answer I wrote 15 minutes ago to the same problem: Retrieving ArrayList<Object> from FireBase inner class 

                        
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