Question

我收到错误消息：

Unhandled Exception: type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'Future <dynamic>`
_LocationScreenState.build.<anonymous closure> 
(package:clima/screens/location_screen.dart:71:32) 
<asynchronous suspension>

精确定位的行在其中：

FlatButton(
   onPressed: () async {
     var weatherData = await weather.getLocationWeather();
     updateUI(weatherData); //<==it's this line
                    },

weather.getLocationWeather()返回类型为Future<dynamic>.的变量，它是JSON，在调试器中对其求值，它是预期的JSON。 upDateUI()方法开始

  void updateUI(Future<dynamic> weatherDataFuture) async {
    final weatherData = await weatherDataFuture;

，然后继续分析所得的weatherData。它在程序的前面被调用，并且按预期工作。我敢肯定，这个问题与我永无止境但仍在继续努力理解异步编程有关：-）

Answer 1

await weather.getLocationWeather()得到getLocationWeather返回的未来，并等待其完成一个值。该值是一张地图。

然后，您将使用该映射值调用updateUI，即使它期望将来也是如此。该变量的类型为dynamic，因此您不会收到任何静态警告，而只会收到运行时错误。

   onPressed: () async {
     var weatherData = await weather.getLocationWeather();
     updateUI(weatherData); //<==it's this line

尝试删除await。这样weatherData将是Future<dynamic>，它恰好是updateUI期望的类型。（然后，您还可以从函数中删除async。）

Answer 2

尝试一下：

final weatherData;
Future<Map<String, dynamic>> weatherDataFuture async{
  return weather.getLocationWeather();
}

FlatButton(
  onPressed: () {
  weatherDataFuture.then((value){
   weatherData=value.values;
 });
} 
)

Answer 3

获取数据的返回值需要强制转换。我建议您查阅flutter文档中的JSON教程。

    FlatButton(
       onPressed: () async {
         var weatherData = Map<String, dynamic>.from(await weather.getLocationWeather());
         updateUI(weatherData); //<==it's this line
    },

void updateUI(Map<String, dynamic> weatherData) async {
    ...

=====根据评论进行编辑=====

FlatButton(
    onPressed: () async {
      var weatherData = SynchronousFuture(Map<String, dynamic>.from(await weather.getLocationWeather()));
      updateUI(weatherData); //<==it's this line
},

void updateUI(Future<Map<String, dynamic>> weatherData) async {
    ...

未处理的异常：类型'_InternalLinkedHashMap <String，dynamic>'不是类型'Future <dynamic>'的子类型

3 个答案: