火力地堡數據庫異常

Question

這裏就是我打算讀火力數據庫的位置類型的數據項，並將其存儲在一個位置類型對象的類。我甚至嘗試將數據快照存儲在構造函數中具有位置類型參數的類的對象中，我得到的錯誤說明如下：

「com.google.firebase.database.DatabaseException：Class android.location。位置缺少一個沒有參數的構造函數「

package com.example.aadi.sarthi_; 
import android.content.Context; 
import android.content.Intent; 
import android.location.Location; 
import android.os.Bundle; 
import android.support.annotation.Nullable; 
import android.support.v4.app.Fragment; 
import android.support.v7.widget.LinearLayoutManager; 
import android.support.v7.widget.RecyclerView; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
import com.google.firebase.database.ChildEventListener; 
import com.google.firebase.database.DataSnapshot; 
import com.google.firebase.database.DatabaseError; 
import com.google.firebase.database.DatabaseReference; 
import com.google.firebase.database.FirebaseDatabase; 
import com.google.firebase.database.ValueEventListener; 

import java.util.ArrayList; 
import java.util.List; 


public class ActiveNotifications extends Fragment{ 
    public static final String NOTIFICATION_MSG = "NOTIFICATION MSG"; 
    public RecyclerView recyclerView; 

    String user_mac; 
    public List<notifyListRowItem> result; 
    public UserAdapter userAdapter; 
private  DatabaseReference reference = FirebaseDatabase.getInstance().getReference(); 
private  DatabaseReference eventRef = reference.child("Events"); 

    // Create a Intent send by the notification 
    public static Intent makeNotificationIntent(Context context, String msg) { 
     Intent intent = new Intent(context, ActiveNotifications.class); 
     intent.putExtra(NOTIFICATION_MSG, msg); 
     return intent; 
    } 

    @Nullable 
    @Override 
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 
     View view = inflater.inflate(R.layout.activity_active_notifications, container, false); 
     getMac(); 
     result = new ArrayList<>(); 
     recyclerView = (RecyclerView) view.findViewById(R.id.notification_list); 
     recyclerView.setHasFixedSize(true); 
     LinearLayoutManager rlm = new LinearLayoutManager(getActivity()); 
     rlm.setOrientation(LinearLayoutManager.VERTICAL); 

     recyclerView.setLayoutManager(rlm); 
     /* 
     createNotifyListRowItem();*/ 
     userAdapter = new UserAdapter(result); 
     recyclerView.setAdapter(userAdapter); 
     updateList(); 
     return view; 
    } 
    @Override 
    public boolean onContextItemSelected(MenuItem item) { 

     switch (item.getItemId()){ 
      case 0: 
       break; 
      case 1: 
       break; 
     } 

     return super.onContextItemSelected(item); 
    } 
    public void updateList(){ 
     final DatabaseReference locationRef = reference.child(String.valueOf(user_mac)).child("location"); 
     final Location userLoc = null; 
     final Location eventLoc = null; 

     locationRef.addListenerForSingleValueEvent(new ValueEventListener() { 
      @Override 
      public void onDataChange(DataSnapshot dataSnapshot) { 
       if(dataSnapshot.exists()) { 

        Location location = dataSnapshot.getValue(Location.class); 
       userLoc.set(location); 

       } 

      } 

      @Override 
      public void onCancelled(DatabaseError databaseError) { 

      } 
     }); 
     eventRef.limitToFirst(2).addChildEventListener(new ChildEventListener() { 
      @Override 
      public void onChildAdded(DataSnapshot dataSnapshot, String s) { 
       eventRef.push().child("location"); 
       Location location = dataSnapshot.getValue(Location.class); 
       eventLoc.set(location); 

       if(eventLoc.distanceTo(userLoc)<=1000) { 
        result.add(dataSnapshot.getValue(notifyListRowItem.class)); 

        userAdapter.notifyDataSetChanged(); 

       } 

      } 

      @Override 
      public void onChildChanged(DataSnapshot dataSnapshot, String s) { 
       Log.w("asd", "In onChildChanged"); 
       notifyListRowItem notifyListRowItem = dataSnapshot.getValue(notifyListRowItem.class); 
       int index = getItemIndex(notifyListRowItem); 
       result.set(index,notifyListRowItem); 
       userAdapter.notifyItemChanged(index); 
      } 

      @Override 
      public void onChildRemoved(DataSnapshot dataSnapshot) { 

       Log.w("In ", "OnchildRemoved"); 
       notifyListRowItem model = dataSnapshot.getValue(notifyListRowItem.class); 
       int index = getItemIndex(model); 
       result.remove(index); 
       userAdapter.notifyItemRemoved(index); 

      } 

      @Override 
      public void onChildMoved(DataSnapshot dataSnapshot, String s) { 
       Log.w("IN", "onChildMoved"); 
      } 

      @Override 
      public void onCancelled(DatabaseError databaseError) { 
       Log.w("IN", "onChildCancelled"); 
       return; 
      } 
     }); 
    } 
    private int getItemIndex(notifyListRowItem item){ 
     int index = -1; 

     for (int i=0;i<result.size();i++){ 
      if(result.get(i).key.equals(item.key)){ 
       index = i; 
       break; 
      } 
     } 
     return index; 
    } 
    protected void getMac(){ 
     GettingMac gettingMac = new GettingMac(getActivity()); 
     user_mac = gettingMac.Mac(); 
    } 
} 

Answer 1

您需要爲Location類提供一個空的構造函數。

public Location() {} 

Answer 2

您應該需要添加您的位置類的構造函數。

public Location() { 

}