Question

我有一些代码从Firebase获取数据，但是工作正常，但是停止了工作。 ValueEventListener中的所有内容都会被跳过，因为它给了我一个错误：＆＃39;没有这样的实例字段：＆＃39; mDatabase＆＃39;。我怎样才能解决这个问题？我已经尝试重新启动Android Studio和我的电脑，但它一直给我这个错误......

代码：

mDatabase = FirebaseDatabase.getInstance().getReference();

ValueEventListener dataListener = new ValueEventListener() {

    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {

          // Make list for ReisData objects
          reisDataList = new ArrayList<ReisData>();

          // Put objects from database into java object list
          for (DataSnapshot ds : dataSnapshot.child("allData").getChildren()) {
               data = ds.getValue(ReisData.class);
               reisDataList.add(data);
          }

     }

     @Override
     public void onCancelled(DatabaseError databaseError) {
         // Getting data failed, log a message
         Log.w("Error:", databaseError.toException());
     }
 };
 mDatabase.addValueEventListener(dataListener);

编辑：我想我可能已经发现了这个问题。在此代码下，我添加了一些代码来显示reisDataList的内容，这似乎会干扰ValueEventListener。有没有办法运行这段代码而不会出现任何错误？

添加了代码：

    MyTripsAdapter myTripsAdapter = new MyTripsAdapter(getContext(), reisDataList);
    ListView listView = (ListView) view.findViewById(R.id.mijnReizenList);
    listView.setAdapter(myTripsAdapter);*/

Answer 1

此代码可以帮助您解决问题。

公共类Map_Activity扩展了AppCompatActivity {

private DatabaseReference databaseRefer;
private FirebaseDatabase mFirebaseInstance;
private ArrayList<Location> reisDataList = new ArrayList<>();
private MyTripsAdapter myTripsAdapter;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_maps);

    mFirebaseInstance = FirebaseDatabase.getInstance(); //getting instance of FireDatabase

    //getting db reference from specific node, here you're not refering the node
    databaseRefer = mFirebaseInstance.getReference("windfirm/future");  

    ListView listView = (ListView) view.findViewById(R.id.mijnReizenList);

    databaseRefer.addListenerForSingleValueEvent(new ValueEventListener() {

       @Override
       public void onDataChange(DataSnapshot dataSnapshot) {

        // pendingCount is the count for dataSnapshot children
        long[] pendingCount = { dataSnapshot.getChildrenCount() };

       //parsing all the node list data from dataSnapshot
         for (DataSnapshot child : dataSnapshot.getChildren()) {


               String rightLocation = child.child("lat").getValue().toString();
               String leftLocation = child.child("lon").getValue().toString();
               String city = child.child("city").getValue().toString();
               reisDataList.add(new  Location(rightLocation, leftLocation, city)); //adding object to arraylist

            // we loaded a child, check if we're done
               pendingCount[0] = pendingCount[0] - 1;
               if (pendingCount[0] == 0) {
                   myTripsAdapter = new MyTripsAdapter(getContext(), reisDataList);
                  listView.setAdapter(myTripsAdapter);
               }               


           }


       }

       @Override
       public void onCancelled(DatabaseError databaseError) {

       }
   });


  }

}

Firebase＆＃39;没有这样的实例字段＆＃39;错误

1 个答案: