火力基地'no such instance field'错误

Question

我有一些代码从Firebase获取数据，这些代码有效，但不知何故停止工作。ValueEventListener中的所有内容都被跳过，因为它给了我一个错误："没有这样的实例字段："mDatabase"。我该如何解决这个问题？我试过重新启动安卓工作室和我的电脑，但它一直给我这个错误......

法典：

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：我想我可能已经找到了问题。在此代码下，我添加了一些代码来显示reisDataList的内容，这似乎干扰了ValueEventListener。有没有办法运行此代码而不会出现任何错误？

添加的代码：

    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) {
       }
   });

  }

}