Question

尝试从我的Firebase中名为category的子项中检索数据，并将其保存在名为testList的List中。问题是该列表最终为空。我究竟做错了什么？

{
  "elements" : {
    "element_id_0" : {
      "description" : "While laying flat on your back, arms at 90 degrees etc",
      "name" : "Bench press"
    },
    "element_id_1" : {
      "description" : "Incline the backboard 30 degrees and etc etc",
      "name" : "Incline Dumbbell Press"
    }
  },
  "workouts" : {
    "workout_id_0" : {
      "category" : "Heavy Chest and Arms",
      "elements" : {
        "element_id_0" : "true",
        "element_id_1" : "true"
      }
    },
    "workout_id_1" : {
      "category" : "Light Back and Shoulders",
      "elements" : {
        "element_id_0" : "true"
      }
    }
  }
}

我使用的一些应用程序代码。

 myFirebaseRef = new Firebase("https://myfirebase.firebaseio.com/workouts");
    myFirebaseRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot snapshot) {
            for (DataSnapshot child : snapshot.getChildren()) {


                testList.add(child.child("category").getValue().toString());

            }
        }



        @Override
        public void onCancelled(FirebaseError firebaseError) {

        }
    });

我也试过这个，而不是上面的，这也不起作用......

 Firebase myFirebaseRef;
    List<String> testList;
    long räknare;
     private static final String TAG = "Anders";

    // ArrayAdapter<Integer> timeAdapter;
   // ArrayAdapter<CharSequence> timeAdapter;
    List<String> messages;

    Integer[] sets= {1,2,3,4,5};


    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        Firebase.setAndroidContext(this);
        setContentView(R.layout.activity_start);

        myFirebaseRef = new Firebase("https://myfirebaseio.com/workouts");

        myFirebaseRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                //Log.d("There are " + dataSnapshot.getChildrenCount() + " workouts");
                for (DataSnapshot workoutSnapshot: dataSnapshot.getChildren()) {
                    Workout workout = workoutSnapshot.getValue(Workout.class);
                    testList.add(workout.getcategory());
                }


            }

            @Override
            public void onCancelled(FirebaseError firebaseError) {

            }
        });

我为此创建了一个Workout类：

package org.example.anders.eazy;

import com.fasterxml.jackson.annotation.JsonIgnore;

/**
 * Created by Anders on 2016-02-28.
 */
public class Workout {


   // private String workouts;
    @JsonIgnore
    private String category;
    private String elements;


    private Workout() {}
        // empty default constructor, necessary for Firebase to be able to deserialize blog posts

  /*  Workout(String category,String elements){
        this.category=category;
        this.elements=elements;
    }
*/
//    public String getWorkout() {
//
//        return workouts;
//    }
    public String getcategory() {
        return category;
    }
}

Answer 1

也许再加一个孩子

myFirebaseRef = new Firebase("https://myfirebase.firebaseio.com/workouts");
myFirebaseRef.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot snapshot) {
        for (DataSnapshot child : snapshot.getChildren()) {


            testList.add(child.child.child("category").getValue().toString());  <------- Here

        }
    }



    @Override
    public void onCancelled(FirebaseError firebaseError) {

    }
});

Answer 2

你无法真正按照自己的要求行事：

如果您想要检索一个类别并且您知道路径，那很容易

ref = new Firebase("https://myfirebase.firebaseio.com/workouts/workout_id_1/category");
ref.addListenerForSingleValueEvent etc etc

那将返回那个（也就是那个）路径的值，即“Light Back and Shoulders”

如果要获取所有类别，则需要读入所有训练节点，然后从快照中提取类别。

此外，请注意您之前问题的答案也包含对此问题的回答：

Getting objects out from Firebase(Json)

从firebase

2 个答案: