I'm getting the following error after building my flutter app after i run the flutter run:

type 'Null' is not a subtype of type 'String' in type cast

The trace that is observed is as follows :

I/flutter ( 8093): type 'Null' is not a subtype of type 'String' in type cast
I/flutter ( 8093): #0      new Future.value (dart:async/future.dart:349:59)
I/flutter ( 8093): #1      ProxySettings.findProxy (package:Myapp/plugins/proxy_settings.dart:14:21)
I/flutter ( 8093): #2      MyAppProviderState.initAsyncState (package:Myapp/provider.dart:215:39)
I/flutter ( 8093): <asynchronous suspension>
I/flutter ( 8093): In dev mode. Not sending report to Sentry.io.
I/flutter ( 8093): Clearing prompted user for permission


provider.dart

void initAsyncState() async {
    Environment environment =
        await EnvironmentLoader(environmentPath: ".env.json").load();
    httpService.setMagicHeader(
        environment.magicHeaderName, environment.magicHeaderValue);
    httpService
        .setProxy(await ProxySettings.findProxy(Uri.parse(environment.apiUrl))); --> Line 215 which is shown in the trace(provider.dart).
        
environment_loader.dart

import 'dart:async' show Future;
import 'dart:convert' show json;
import 'package:flutter/services.dart' show rootBundle;

class EnvironmentLoader {
  final String? environmentPath;

  EnvironmentLoader({this.environmentPath});

  Future<Environment> load() {
    return rootBundle.loadStructuredData<Environment>(this.environmentPath!,
        (jsonStr) async {
      final environmentLoader = Environment.fromJson(json.decode(jsonStr));
      return environmentLoader;
    });
  }
}

class Environment {
  final String apiUrl;
  final String magicHeaderName;
  final String magicHeaderValue;
  // final String intercomIosKey;
  // final String intercomAndroidKey;
  // final String intercomAppId;
  final String sentryDsn;
  final String myappapiurl;
  final String linkPreviewsTrustedProxyUrl;

  const Environment(
  {
    this.sentryDsn = '',
    this.myappapiurl = '',
    this.apiUrl = '',
    this.magicHeaderName = '',
    this.magicHeaderValue = '',
    // this.intercomAndroidKey = '',
    // this.intercomAppId = '',
    this.linkPreviewsTrustedProxyUrl = '',
    // this.intercomIosKey = ''
  });

  factory Environment.fromJson(Map<String, dynamic> jsonMap) {
    return new Environment(
      apiUrl: jsonMap["API_URL"],
      magicHeaderName: jsonMap["MAGIC_HEADER_NAME"],
      magicHeaderValue: jsonMap["MAGIC_HEADER_VALUE"],
      // intercomAppId: jsonMap["INTERCOM_APP_ID"],
      // intercomIosKey: jsonMap["INTERCOM_IOS_KEY"],
      // intercomAndroidKey: jsonMap["INTERCOM_ANDROID_KEY"],
      sentryDsn: jsonMap["SENTRY_DSN"],
      myappapiurl: jsonMap["KOSMOSNETWORK_SOCIAL_API_URL"],
      linkPreviewsTrustedProxyUrl: jsonMap["LINK_PREVIEWS_TRUSTED_PROXY_URL"],
    );
  }
}

.env.json

{
  "API_URL": "http://'mydomain':80/",
  "MAGIC_HEADER_NAME": "",
  "MAGIC_HEADER_VALUE": "",
  "SENTRY_DSN": "",
  "APP_SOCIAL_API_URL": "http://'mydomain':80/",
  "LINK_PREVIEWS_TRUSTED_PROXY_URL": "http://'mydomain':80/"
}

AndroidManifest.xml

<intent-filter android:autoVerify="true">
                <action android:name="android.intent.action.VIEW"/>
                <category android:name="android.intent.category.DEFAULT"/>
                <category android:name="android.intent.category.BROWSABLE"/>
                <data
                        android:scheme="http"
                        android:host="mydomain" -->without port
                        android:pathPrefix="/api/auth/"/>
            </intent-filter>
            <intent-filter android:autoVerify="true">
                <action android:name="android.intent.action.VIEW"/>
                <category android:name="android.intent.category.DEFAULT"/>
                <category android:name="android.intent.category.BROWSABLE"/>
                <data
                        android:scheme="https"
                        android:host="mydomain" -->without port
                        android:pathPrefix="/api/auth/"/>
        

Kindly help. I'll provide more information if needed.Thanks in advance. Dont know but I feel the above could br related to the follwoing question i posted as a separate question :

LateInitializationError: Field 'apiURL' has not been initialized

CodePudding user response：

Your value from api is null when you try to parse it, you need set default value to them. Change your fromJson to this:

factory Environment.fromJson(Map<String, dynamic> jsonMap) {
    return new Environment(
      apiUrl: jsonMap["API_URL"] ?? "",
      magicHeaderName: jsonMap["MAGIC_HEADER_NAME"] ?? "",
      magicHeaderValue: jsonMap["MAGIC_HEADER_VALUE"] ?? "",
      // intercomAppId: jsonMap["INTERCOM_APP_ID"] ?? "",
      // intercomIosKey: jsonMap["INTERCOM_IOS_KEY"] ?? "",
      // intercomAndroidKey: jsonMap["INTERCOM_ANDROID_KEY"] ?? "",
      sentryDsn: jsonMap["SENTRY_DSN"] ?? "",
      myappapiurl: jsonMap["KOSMOSNETWORK_SOCIAL_API_URL"] ?? "",
      linkPreviewsTrustedProxyUrl: jsonMap["LINK_PREVIEWS_TRUSTED_PROXY_URL"] ?? "",
    );
  }

or define your model's variables as nullable:

class Environment {
  final String? apiUrl;
  final String? magicHeaderName;
  final String? magicHeaderValue;
  // final String? intercomIosKey;
  // final String? intercomAndroidKey;
  // final String? intercomAppId;
  final String? sentryDsn;
  final String? myappapiurl;
  final String? linkPreviewsTrustedProxyUrl;
...
}

both above ways are correct but you decide which one is works for you.