在这段代码中，我得到了无法为child（）中的参数'path string'传递null的错误

Question

我最近将firebase数据库的订单更改为Location，我知道我漏了一些东西，但我找不到确切的问题。有人能指出我在这里做错了什么吗？

package com.example.policeemergencysystem;

import android.os.Bundle;

import androidx.fragment.app.FragmentActivity;

import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
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;

public class AdminViewMapsActivity extends FragmentActivity implements OnMapReadyCallback {

    private GoogleMap mMap;
    DatabaseReference mMaps;
    private String userID = "";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_admin_view_maps);
        userID = getIntent().getStringExtra("uid");


        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);

        mMaps = FirebaseDatabase.getInstance().getReference().child("Location").child(userID);
    }


    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;

        mMaps.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {

                double latitude = dataSnapshot.child("latitude").getValue(Double.class);
                double longitude = dataSnapshot.child("longitude").getValue(Double.class);
                LatLng latLng = new LatLng(latitude, longitude);
                mMap.addMarker(new MarkerOptions().position(latLng).title("Location"));
                CameraPosition cameraPosition = new CameraPosition.Builder()
                        .target(latLng)
                        .zoom(12).build();
                //Zoom in and animate the camera.
                mMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));

            }
            @Override
            public void onCancelled(DatabaseError databaseError) {
            }
        });
    }
}

Answer 1

您的数据库显示没有uid，而只有硬编码的管理名称。

mMaps = FirebaseDatabase.getInstance().getReference().child("Location").child("admin");

使用上面的数据库引用。