在手机上看不到地图

Question

我使用google_map_flutter在移动应用上创建了地图，但我的应用未显示地图。

 import 'dart:async';
 import 'package:flutter/material.dart';
 import 'package:google_maps_flutter/google_maps_flutter.dart';



 class AgentPosition extends StatefulWidget {
 @override
 _AgentPositionState createState() => _AgentPositionState();
 }




 class _AgentPositionState extends State<AgentPosition> {

 CameraPosition _initialPosition = CameraPosition(target: 
 LatLng(7.365302, 12.343439));
 Completer<GoogleMapController> _controller = Completer();

 void _onMapCreated(GoogleMapController controller) {
 _controller.complete(controller);
 }

 MapType _defaultMapType = MapType.normal;

 void _changeMapType(){
 setState((){
 _defaultMapType = _defaultMapType == MapType.normal ? 
 MapType.satellite : MapType.normal;
  });
  }

  @override
  Widget build(BuildContext context) {
  return Scaffold(
  body: Stack(
   children: <Widget>[
     GoogleMap(
      mapType: _defaultMapType,
      myLocationEnabled: true,
      onMapCreated: _onMapCreated,
      initialCameraPosition: _initialPosition,
  ),
  Container(
    margin: EdgeInsets.only(top: 80, right: 10),
    alignment: Alignment.topRight,
    child: Column(
      children: <Widget>[
        FloatingActionButton(
            child: Icon(Icons.layers),
            elevation: 5,
            backgroundColor: Colors.teal[200],
            onPressed: (){
              _changeMapType();
              print('Changing the Map Type');
            }
        )
      ],
    ),
  )
],
) ,
);
}
}