Flutter 未来执行后不显示窗口小部件

安卓工作室4

颤振工程

下面是一段：

import 'package:flutter/cupertino.dart';
import 'package:geolocator/geolocator.dart';
import 'package:permission_handler/permission_handler.dart';

 Future<bool> isGeolocationStatusDisabled() async {
  GeolocationStatus geolocationStatus = await getGeolocationStatus();
  return (geolocationStatus == GeolocationStatus.disabled);
}

 Widget _createMapInnerContainerLeft() {
    _logger.d("_createMapInnerContainerLeft: -> call_async_isGeolocationStatusDisabled()");
    return _createTurnOffGlobalLocationServiceContainerLeft();
  }




Widget _createTurnOffGlobalLocationServiceContainerLeft() {
    _logger.d("_createTurnOffGlobalLocationServiceContainerLeft:");
    return new Container(
        margin: const EdgeInsets.only(
            left: Constants.DEFAULT_MARGIN, top: Constants.DEFAULT_MARGIN),
        child:
            new Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
          new Text("Geolocation service is turned off",
              style: _createNearestGazStationTextViewStyle(FontWeight.bold)),
          new Text("Turn on geolocation for the application",
              style: _createNearestGazStationTextViewStyle()),
          new Align(
              alignment: Alignment.center,
              child: new Padding(
                  padding: EdgeInsets.only(top: Constants.DEFAULT_MARGIN),
                  child: new RaisedButton(
                      onPressed: () {
                        _logger.d("click");
                      },
                      child: Text('Settings'.toUpperCase(),
                          style: _createNearestGazStationTextViewStyle()),
                      color: new Color(Constants.COLOR_PRIMARY),
                      textColor:
                          new Color(Constants.COLOR_PRIMARY_TEXT_COLOR))))
        ]));
  }

现在小部件不显示：

---

获得空白的原因是函数返回

null

，因为这是

Dart

函数的默认行为，函数不会在所有条件路径上返回值

未处理条件路径的原因是，您没有使用

await

关键字等待

将来的执行，因此程序开始执行
isGeolocationStatusDisabled
函数，但不等待结果

您应该使用
FutureBuilder
根据
Future
执行的结果呈现
Widget

Widget _createMapInnerContainerLeft() {
  return FutureBuilder(
    future: isGeolocationStatusDisabled(),
    builder: (context, futureData) {
      if (futureData.hasData) {
        _logger.d("_createMapInnerContainerLeft: -> call_async_isGeolocationStatusDisabled()");
        bool isGeolocationStatusDisabledFuture = futureData.data;
        if (isGeolocationStatusDisabledFuture) {
          return _createTurnOffGlobalLocationServiceContainerLeft();
        }
      }

      return CircularProgressIndicator();
    }
  )
}

查看页面以了解有关
FutureBuilder
的更多信息。您还可以阅读有关Dart的更多信息，如异步编程，此帮助：

Widget _createMapInnerContainerLeft() {
    _logger.d(
        "_createMapInnerContainerLeft: -> call_async_isGeolocationStatusDisabled()");
    return FutureBuilder(
        future: isGeolocationStatusDisabled(),
        builder: (context, projectSnap) {
          ConnectionState connectionState = projectSnap.connectionState;
          bool hasData = projectSnap.hasData;
          _logger.d("_createMapInnerContainerLeft: connectionState = $connectionState, hasData = $hasData");
          if (connectionState == ConnectionState.done &&  hasData != null) {
            _logger.d("_createMapInnerContainerLeft: -> call_showNearestGazStationViewMode");
            return _showNearestGazStationViewMode();;
          }
          _logger.d("_createMapInnerContainerLeft: -> call_Container()");
          return Container();
        });
  }


Future<bool> isGeolocationStatusDisabled() async {
  GeolocationStatus geolocationStatus = await getGeolocationStatus();
  return (geolocationStatus == GeolocationStatus.disabled);
}

Widget\u createMapinerContainerLeft（）{
_记录器.d(
“\u createMapinerContainerLeft:->调用\u async\u isGeolocationStatusDisabled（）”；
回归未来建设者(
未来：isGeolocationStatusDisabled（），
生成器：（上下文，projectSnap）{
ConnectionState ConnectionState=projectSnap.ConnectionState；
bool hasData=projectSnap.hasData；
_d（“_createMapinerContainerLeft:connectionState=$connectionState，hasData=$hasData”）；
if（connectionState==connectionState.done&&hasData！=null）{
_logger.d（“\u createMapinerContainerLeft:->调用\u showNearestGazStationViewMode”）；
返回_showNearestGazStationViewMode（）；；
}
_logger.d（“\u createMapinerContainerLeft:->call\u Container（）”；
返回容器（）；
});
}
未来isGeolocationStatusDisabled（）异步{
GeolocationStatus GeolocationStatus=等待getGeolocationStatus（）；
返回（geolocationStatus==geolocationStatus.disabled）；
}
您应该使用@Neil的答案，但您应该注意编译器警告/信息。您应该已经看到了关于该函数的一些内容，它不是以
return
语句结尾的。
Widget _createMapInnerContainerLeft() {
    _logger.d(
        "_createMapInnerContainerLeft: -> call_async_isGeolocationStatusDisabled()");
    return FutureBuilder(
        future: isGeolocationStatusDisabled(),
        builder: (context, projectSnap) {
          ConnectionState connectionState = projectSnap.connectionState;
          bool hasData = projectSnap.hasData;
          _logger.d("_createMapInnerContainerLeft: connectionState = $connectionState, hasData = $hasData");
          if (connectionState == ConnectionState.done &&  hasData != null) {
            _logger.d("_createMapInnerContainerLeft: -> call_showNearestGazStationViewMode");
            return _showNearestGazStationViewMode();;
          }
          _logger.d("_createMapInnerContainerLeft: -> call_Container()");
          return Container();
        });
  }


Future<bool> isGeolocationStatusDisabled() async {
  GeolocationStatus geolocationStatus = await getGeolocationStatus();
  return (geolocationStatus == GeolocationStatus.disabled);
}