Question

我正在尝试获取当前在“历史记录”节点中的游乐设施的“状态”，但首先我必须获取“ rideKey”。

全局变量：字符串rideKey，字符串键。

历史节点：

{
  "History" : {
    "-LGXaukR30LTjrL3ZNpt" : {
      "driver" : "ptnVOKounjXE9VrmZCCvKoZWluf1",
      "rating" : 0,
      "ridePrice" : 5.25,
      "rider" : "C0RjB5NPZcTvWz9XiUAhpTDOK0C2",
      "status" : "accepted",
      "timestamp" : 1530662726
    }
  }
}

要获取rideKey，我是这样做的：

    DatabaseReference keyRef = FirebaseDatabase.getInstance().getReference("History");
    keyRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            rideKey = String.valueOf(mDatabase.child("History").push().getKey());
            Log.d(TAG, "getKey: key = " + rideKey);
        }

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

这为我提供了历史记录中的所有键，如何获得最新的键？

现在，我还需要获取请求的“状态”。

但是，当我尝试获取状态时，它一直显示为空。
我尝试将另一个ValueEventListener放入rideKey值事件中，但仍然为空

关于我在做什么错的任何想法吗？ 非常感谢。

编辑

Log.e(TAG, "I made it to getKeyAndStatus");

    DatabaseReference keyRef = FirebaseDatabase.getInstance().getReference("History");
    keyRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
**// Log.e(TAG, "I made it to getKeyAndStatus: onDataChange");**

            Iterable<DataSnapshot> children = dataSnapshot.child("History").getChildren();

            for (DataSnapshot child : children){
                Log.d(TAG, "getKey: key = " + child.getKey());

                Ride ride = child.getValue(Ride.class);
                Log.e(TAG, "ride = " + ride);

                Log.d(TAG, "Driver = " + ride.getDriver());
                Log.d(TAG, "Rating = " + ride.getRating());
                Log.d(TAG, "Rider = " + ride.getRider());
                Log.d(TAG, "Price = " + ride.getRidePrice());
                Log.d(TAG, "status = " + ride.getStatus());
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

上面的代码仅使它到达日志“我将其设置为getKeyAndStatus：onDataChange”

编辑-结果

Answer 1

要解决此问题，请使用以下代码：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference historyRef = rootRef.child("History");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            Ride ride = ds.getValue(Ride.class);

            Log.d(TAG, "Driver = " + ride.getDriver());
            Log.d(TAG, "Rating = " + ride.getRating());
            Log.d(TAG, "Rider = " + ride.getRider());
            Log.d(TAG, "Price = " + ride.getRidePrice());
            Log.d(TAG, "status = " + ride.getStatus());
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
historyRef.addListenerForSingleValueEvent(valueEventListener);

logcat中的输出将是属性的值。

请注意，使用以下代码行时：

rideKey = String.valueOf(mDatabase.child("History").push().getKey());

您正在生成另一个密钥，而不是获取现有密钥。仅在添加对象时才使用push()方法，而在阅读对象时则不使用。

Answer 2

DatabaseReference keyRef = FirebaseDatabase.getInstance().getReference("History");
keyRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        rideKey = String.valueOf(mDatabase.child("History").push().getKey());
        Log.d(TAG, "getKey: key = " + rideKey);

        DatabaseReference statusRef = FirebaseDatabase.getInstance().getReference("History").Child(rideKey).Child("status");
statusRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            History history = new History(); //If you make class for history
            history = dataSnapshot.getValue(History.class);
            textViewStatus.setText(history.getStatus());
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

Answer 3

DatabaseReference historyRef = FirebaseDatabase.getInstance().getReference().child("History");

    historyRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot child : dataSnapshot.getChildren()){
                Log.d(TAG, "getKey: key = " + child.getKey());

                Ride ride = child.getValue(Ride.class);

                Log.d(TAG, "Driver = " + ride.getDriver());
                Log.d(TAG, "Rating = " + ride.getRating());
                Log.d(TAG, "Rider = " + ride.getRider());
                Log.d(TAG, "Price = " + ride.getRidePrice());
                Log.d(TAG, "status = " + ride.getStatus());
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

//
//       "driver" : "ptnVOKounjXE9VrmZCCvKoZWluf1",
//               "rating" : 0,
//               "ridePrice" : 5.25,
//               "rider" : "C0RjB5NPZcTvWz9XiUAhpTDOK0C2",
//               "status" : "accepted",
//               "timestamp" : 1530662726

class Ride{
    // Remove @Exclude https://firebase.google.com/docs/reference/android/com/google/firebase/database/Exclude
    private String driver;
    private int rating;
    private float ridePrice;
    private String rider;
    private String status;
    private long timestamp;

    public Ride() {
      // Empty Constructor  
    }
      // Getter & Setter 
  }

android：获取孩子的孩子

3 个答案: