Flutter：在 null 上调用了方法“animateCamera”答案

【问题标题】：Flutter : The method 'animateCamera' was called on nullFlutter：在 null 上调用了方法“animateCamera”
【发布时间】：2020-11-23 12:36:36
【问题描述】：

我有这个应用程序：

我想在点击floatingActionButton时缩小一点，但它会抛出这个异常

The method 'animateCamera' was called on null.
Receiver: null
Tried calling: animateCamera(Instance of 'CameraUpdate')

这是我的代码：

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

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {


  @override
  void initState() {
  }

  @override
  Widget build(BuildContext context) {
    GoogleMapController _controller;
    final CameraPosition _initialPosition = CameraPosition(target: LatLng(24.903623, 67.198367));
    return Scaffold(
      backgroundColor: Colors.white,
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: GoogleMap(
        initialCameraPosition: _initialPosition,
        mapType: MapType.normal,
        onMapCreated: (controller){
          setState(() {
            _controller = controller;
          });
        },
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: (){
          _controller.animateCamera(CameraUpdate.zoomOut());
        },
        child: Icon(Icons.zoom_out),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }

}

如何解决？

【问题讨论】：

热重启应用。看起来你在地图创建后添加了_controller
这能回答你的问题吗？ What is a NoSuchMethod error and how do I fix it?
请参考medium.com/flutterdevs/location-in-flutter-27ca6fa1126c

标签： android ios flutter dictionary dart

【解决方案1】：

这是因为您调用的 mapController 为 null！

mapController.animateCamera();

听起来像你这样删除“GoogleMapController mapController;”

我会建议您使用 GoogleMapController 类型的 Completer，然后将其集成到“OnMapCreated:”中，控制器由“OnMapCreated”函数返回 Global 部分中的第一个 Decleare Controller，如下所示：Completer<GoogleMapController> _controller = Completer();

然后在 GoogleMaps 内部使用onMapCreated: 函数，如下所示谷歌地图（

onMapCreated: (GoogleMapController controller) {
              _controller.complete(controller);
            },
)

现在如何使用它 1st) : 在调用 animateCamera 函数之前使用这个

final GoogleMapController mapController = await _controller.future;

这将初始化 mapController 然后调用

 mapController.animateCamera()

【讨论】：

【解决方案2】：

重新启动您的应用。也考虑搬家

GoogleMapController _controller;
    final CameraPosition _initialPosition = CameraPosition(target: LatLng(24.903623, 67.198367));

要么进入initstate，要么声明为成员变量

【讨论】：