火力地堡数据库异常

Question

这里就是我打算读火力数据库的位置类型的数据项，并将其存储在一个位置类型对象的类。我甚至尝试将数据快照存储在构造函数中具有位置类型参数的类的对象中，我得到的错误说明如下：

“com.google.firebase.database.DatabaseException：Class android.location。位置缺少一个没有参数的构造函数“

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

您需要为Location类提供一个空的构造函数。

public Location() {} 

Answer 2

您应该需要添加您的位置类的构造函数。

public Location() { 

}