amap

      高德地图的Flutter官方插件：amap_flutter_map 3.0，功能不是非常全，我们常用的一个场景，地图在初始化后，将当前位置设为地图显示的中心，在原生的地图SDK上只需要设置地图的一个属性就可以，但是amap_flutter_map并不支持，需要自己实现。

        AMapWidget有一个属性initialCameraPosition，是用来指定地图的初始中心位置的。从源代码可以看出，如果initialCameraPosition没有指定的话，默认值是北京市。如果使用定位功能取得当前位置后再初始化地图的话，因为取当前位置需要时间较长，界面会出现长时间的空白。如果地图先显示出来，取得当前位置后再用setState的方式更新initialCameraPosition属性的话，地图没有反应。在initialCameraPosition属性上作文章是没有办法了。

       最后用AMapController的moveCamera方法实现了这个功能，但是有一个问题，就是定位需要较长时间，所以在地图显示一段时间后，中心点才移动到当前位置。在将定位精度降低后，在虚拟机上定位时间也没有缩短，现在只能将就用了，希望在真机上定位时间短一些。

        下面是相关代码：

import 'dart:async';

import 'package:amap_flutter_base/amap_flutter_base.dart';
import 'package:amap_flutter_location/amap_flutter_location.dart';
import 'package:amap_flutter_location/amap_location_option.dart';
import 'package:amap_flutter_map/amap_flutter_map.dart';
import 'package:amap_flutter_map_example/base_page.dart';
import 'package:amap_flutter_map_example/const_config.dart';
import 'package:flutter/material.dart';
import 'package:permission_handler/permission_handler.dart';

class MapPage extends BasePage {
  MapPage(String title, String subTitle) : super(title, subTitle);
  @override
  Widget build(BuildContext context) => _Body();
}

class _Body extends StatefulWidget {
  _Body({Key key}) : super(key: key);

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

class _BodyState extends State<_Body> {
  //在按关键字搜索时，传入城市名可以提高搜索精度。
  String _cityName;
  AMapController _mapController;
  Marker _mapMarker;
  Map _locationResult;
  StreamSubscription> _locationListener;
  AMapFlutterLocation _locationPlugin = new AMapFlutterLocation();

  @override
  void initState() {
    super.initState();
    _requestLocaitonPermission();

    AMapFlutterLocation.updatePrivacyShow(true, true);
    AMapFlutterLocation.updatePrivacyAgree(true);
    AMapFlutterLocation.setApiKey("anroid ApiKey", "a6b2356c68aac3fdabd7ecdce63c2130");

    _locationListener = _locationPlugin.onLocationChanged().listen((Map result) {
      setState(() {
        _locationResult = result;
        if (_locationResult != null) {
          _cityName = _locationResult['city'];
          double longitude = double.tryParse(_locationResult['longitude']);
          double latitude = double.tryParse(_locationResult['latitude']);

          print('当前位置：longitude：$longitude,latitude:$latitude');

          _changeCameraPosition(LatLng(latitude, longitude));
        }
      });
    });

    /*
    WidgetsBinding.instance.addPostFrameCallback((_) {
      _startLocation();
    });

     */
    _startLocation();

  }

  ///设置定位参数
  void _setLocationOption() {
    if (null != _locationPlugin) {
      AMapLocationOption locationOption = new AMapLocationOption();

      locationOption.onceLocation = true;
      ///是否需要返回逆地理信息
      locationOption.needAddress = true;
      locationOption.desiredLocationAccuracyAuthorizationMode = AMapLocationAccuracyAuthorizationMode.FullAndReduceAccuracy;

      _locationPlugin.setLocationOption(locationOption);
    }
  }

  ///开始定位
  void _startLocation() {
    if (null != _locationPlugin) {
      _setLocationOption();
      _locationPlugin.startLocation();
    }
  }

  void _requestLocaitonPermission() async {
    PermissionStatus status = await Permission.location.request();
    print('permissionStatus=====> $status');
  }

  @override
  Widget build(BuildContext context) {
    Set markers = Set();
    if (_mapMarker != null) {
      markers.add(_mapMarker);
    }

    AMapWidget aMapWidget = AMapWidget(
      privacyStatement: ConstConfig.amapPrivacyStatement,
      apiKey: ConstConfig.amapApiKeys,
      myLocationStyleOptions: MyLocationStyleOptions(
        true,
        circleFillColor: Colors.lightBlue,
        circleStrokeColor: Colors.blue,
        circleStrokeWidth: 1,
      ),
      markers: markers,
      compassEnabled: true,
      onMapCreated: _onMapCreated,
      onCameraMoveEnd: (cameraPosition) {
        LatLng markerPosition = cameraPosition.target;
        print('=========CameraPosition : ${markerPosition.latitude}');
        Marker marker = Marker(position: markerPosition, icon: BitmapDescriptor.fromIconPath('assets/start.png'));
        setState(() {
          _mapMarker = marker;
        });
      },
    );

    return Container(
      height: MediaQuery.of(context).size.height,
      width: MediaQuery.of(context).size.width,
      child: Column(
        mainAxisAlignment: MainAxisAlignment.start,
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: [
          Container(
            height: MediaQuery.of(context).size.height * 0.6,
            width: MediaQuery.of(context).size.width,
            child: aMapWidget,
          ),
          Expanded(
            child: SingleChildScrollView(
              child: Container(
                child: SizedBox.shrink(),
              ),
            ),
          ),
        ],
      ),
    );
  }

  void _onMapCreated(AMapController controller) {
    setState(() {
      _mapController = controller;
    });
  }

  void _changeCameraPosition(LatLng position) {
    _mapController?.moveCamera(
      CameraUpdate.newCameraPosition(
        CameraPosition(target: position, zoom: 15),
      ),
      animated: true,
    );
  }
}