While calling scnaNetworks() app crashed.

[DhavalRKansara]

While calling ScanNetworks() method Application get crashed and receive below error.

• Code:

_getAvailableWifi() async {
  print("Fetching wifis");
  List<WifiNetwork> filteredList = [];
  bool match = true;

  final networks1 = WifiFlutter.scanNetworks();
  networks1.then((val) {
    val.forEach((result) {
      if (filteredList.isEmpty) {
        filteredList.add(result);
      } else {
        for (WifiNetwork fResult in filteredList) {
          if (result.ssid == fResult.ssid && match) {
            match = false;
          }
        }
        if (match) {
          filteredList.add(result);
        }
        match = true;
      }
    });
    for (WifiNetwork wifi in filteredList) {
      print("secure ${wifi.isSecure} ssid ${wifi.ssid}");
    }
    });
}

• Exception:

I/flutter (10303): Fetching wifis
E/flutter (10303): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: PlatformException(startScan, Unable to start scan., false)
E/flutter (10303): #0      StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:569:7)
E/flutter (10303): #1      MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:316:33)
E/flutter (10303): <asynchronous suspension>
E/flutter (10303): #2      WifiFlutter.scanNetworks (package:wifi_flutter/wifi_flutter.dart:26:37)
E/flutter (10303): <asynchronous suspension>
E/flutter (10303): #3      _getAvailableWifi (package:mqttdemo/main.dart:133:33)
E/flutter (10303): <asynchronous suspension>
E/flutter (10303): #4      _MyHomePageState.build.<anonymous closure> (package:mqttdemo/main.dart:55:17)
E/flutter (10303): #5      _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:654:14)
E/flutter (10303): #6      _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:729:32)
E/flutter (10303): #7      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
E/flutter (10303): #8      TapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:365:11)
E/flutter (10303): #9      TapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:275:7)
E/flutter (10303): #10     PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:455:9)
E/flutter (10303): #11     PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:75:13)
E/flutter (10303): #12     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:102:11)
E/flutter (10303): #13     GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:218:19)
E/flutter (10303): #14     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:198:22)
E/flutter (10303): #15     GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:156:7)
E/flutter (10303): #16     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:102:7)
E/flutter (10303): #17     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:86:7)
E/flutter (10303): #18     _rootRunUnary (dart:async/zone.dart:1136:13)
E/flutter (10303): #19     _CustomZone.runUnary (dart:async/zone.dart:1029:19)
E/flutter (10303): #20     _CustomZone.runUnaryGuarded (dart:async/zone.dart:931:7)
E/flutter (10303): #21     _invoke1 (dart:ui/hooks.dart:263:10)
E/flutter (10303): #22     _dispatchPointerDataPacket (dart:ui/hooks.dart:172:5)
E/flutter (10303): 
D/AndroidRuntime(10303): Shutting down VM
E/AndroidRuntime(10303): FATAL EXCEPTION: main
E/AndroidRuntime(10303): Process: com.example.mqttdemo, PID: 10303
E/AndroidRuntime(10303): java.lang.RuntimeException: Error receiving broadcast Intent { act=android.net.wifi.SCAN_RESULTS flg=0x4000010 pkg=com.example.mqttdemo (has extras) } in com.weplenish.wifi_flutter.WifiScanReceiver@7a2aa6d
E/AndroidRuntime(10303): 	at android.app.LoadedApk$ReceiverDispatcher$Args.lambda$getRunnable$0$LoadedApk$ReceiverDispatcher$Args(LoadedApk.java:1560)
E/AndroidRuntime(10303): 	at android.app.-$$Lambda$LoadedApk$ReceiverDispatcher$Args$_BumDX2UKsnxLVrE6UJsJZkotuA.run(Unknown Source:2)
E/AndroidRuntime(10303): 	at android.os.Handler.handleCallback(Handler.java:883)
E/AndroidRuntime(10303): 	at android.os.Handler.dispatchMessage(Handler.java:100)
E/AndroidRuntime(10303): 	at android.os.Looper.loop(Looper.java:214)
E/AndroidRuntime(10303): 	at android.app.ActivityThread.main(ActivityThread.java:7356)
E/AndroidRuntime(10303): 	at java.lang.reflect.Method.invoke(Native Method)
E/AndroidRuntime(10303): 	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
E/AndroidRuntime(10303): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
E/AndroidRuntime(10303): Caused by: java.lang.IllegalStateException: Reply already submitted
E/AndroidRuntime(10303): 	at io.flutter.embedding.engine.dart.DartMessenger$Reply.reply(DartMessenger.java:151)
E/AndroidRuntime(10303): 	at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler$1.success(MethodChannel.java:225)
E/AndroidRuntime(10303): 	at com.weplenish.wifi_flutter.WifiScanReceiver.onReceive(WifiFlutterPlugin.kt:78)
E/AndroidRuntime(10303): 	at android.app.LoadedApk$ReceiverDispatcher$Args.lambda$getRunnable$0$LoadedApk$ReceiverDispatcher$Args(LoadedApk.java:1550)
E/AndroidRuntime(10303): 	... 8 more

[DhavalRKansara]

Google has now documented the limitations for startScan() function in Android P:

"We are further limiting the number of scans apps can request to improve network performance and improve battery life.

The WifiManager.startScan() usage is limited to: - Each foreground app is restricted to 4 scans every 2 minutes. - All background apps combined are restricted to one scan every 30 minutes."

Source: https://issuetracker.google.com/issues/79906367

Edit 8-Aug-2018: Information has been added also here: https://developer.android.com/guide/topics/connectivity/wifi-scan

[zeeshan0309]

Hey! I too am facing this error, and probably its due to this throttle limitation only. So can I get some help for knowing how exactly can I use this scanNetworks() method encountering this error? Is it totally impossible for us to call the scanNetworks() function, even after (lets say) a gap of 45 seconds or a minute? I tried giving this much of delay between two scanNetworks() calls, but the error persists...

[vipero07]

You need to ensure that you have the correct permissions to make a scan wifi request and you need to make the requests in code before scan wifi is called:
https://pub.dev/packages/permission_handler can get you there.
Don't forget the lines in android's manifest too.

I don't suggest wrapping the error in a try catch as in reality you should require the user grant the necessary permissions before trying to scan networks.

[vipero07]

Depending on your use case though https://github.com/weplenish/flutter_wifi_connect may be a better fit.