Flutter_blue: [Android] Crashes when Bluetooth Adapter is turned off

[ened]

FATAL EXCEPTION: main
Process: com.company.app, PID: 11091
java.lang.RuntimeException: Failure delivering result ResultInfo{who=@android:requestPermissions:, request=1452, result=-1, data=Intent { act=android.content.pm.action.R
EQUEST_PERMISSIONS (has extras) }} to activity {com.company.app/com.company.app.MainActivity}: java.lang.IllegalArgumentException: Unsupported 
value: java.lang.IllegalStateException: getBluetoothLeScanner() is null. Is the Adapter on?
    at android.app.ActivityThread.deliverResults(ActivityThread.java:4339)
    at android.app.ActivityThread.handleSendResult(ActivityThread.java:4382)
    at android.app.ActivityThread.-wrap19(Unknown Source:0)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1654)
    at android.os.Handler.dispatchMessage(Handler.java:105)
    at android.os.Looper.loop(Looper.java:251)
    at android.app.ActivityThread.main(ActivityThread.java:6572)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: java.lang.IllegalArgumentException: Unsupported value: java.lang.IllegalStateException: getBluetoothLeScanner() is null. Is the Adapter on?
    at io.flutter.plugin.common.StandardMessageCodec.writeValue(StandardMessageCodec.java:293)
    at io.flutter.plugin.common.StandardMethodCodec.encodeErrorEnvelope(StandardMethodCodec.java:70)
    at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler$1.error(MethodChannel.java:199)
    at com.pauldemarco.flutterblue.FlutterBluePlugin.startScan(FlutterBluePlugin.java:602)
    at com.pauldemarco.flutterblue.FlutterBluePlugin.onRequestPermissionsResult(FlutterBluePlugin.java:495)
    at io.flutter.app.FlutterPluginRegistry.onRequestPermissionsResult(FlutterPluginRegistry.java:175)
    at io.flutter.app.FlutterActivityDelegate.onRequestPermissionsResult(FlutterActivityDelegate.java:132)
    at io.flutter.app.FlutterActivity.onRequestPermissionsResult(FlutterActivity.java:134)
    at android.app.Activity.dispatchRequestPermissionsResult(Activity.java:7388)
    at android.app.Activity.dispatchActivityResult(Activity.java:7239)
    at android.app.ActivityThread.deliverResults(ActivityThread.java:4335)
    ... 9 more

Plugin should query for Adapter status first and turn it on (Android will prompt the user) before scanning.

[ened]

I see this was intentional in #50, but I would expect it to work the other way. ;-)

[suparnavg]

@ened - did you figure out a way around this? Is there a way to turn the adapter on in case it is off?

[ened]

@suparnavg yes, with the help of the android_intent plugin:

First, check for the bluetooth state and handle cases for devices without bluetooth functions (emulator etc).

final btState =
    await flutterBlue.state.catchError((e) => BluetoothState.unavailable);
if (btState == BluetoothState.unavailable) {
  // notify the error
  return;
}

Finally, prompt the user to activate Bluetooth:

if (btState != BluetoothState.on) {
  if (Platform.isAndroid) {
    // This will trigger a dialog ("Application wants to turn on Bluetooth, do you want to allow it?")
    const intent = AndroidIntent(
      action: 'android.bluetooth.adapter.action.REQUEST_ENABLE',
    );
    await intent.launch();

    // We wait 5 seconds - fixed.
    // This is a tricky bit, because if the user waits on the aforementioned dialog for more than 5 seconds, we still have a disabled bluetooth adapter below.
    // Also can not wait forever, so prepare your UI to switch back to a "un-connected" status.
    await Future.delayed(Duration(seconds: 5));
  }

  if (await flutterBlue.state != BluetoothState.on) {
    // Switch UI back to "not connected".
    return;
  }
}

[andretietz]

This (or similar) code should be part of the plugin.

[suparnavg]

@ened thanks for the tip!

[joe733]

@ened, thanks for the workaround. When I implemented the same, it gave me these:

• The method 'catchError' isn't defined for the type 'Stream'. _error_, so I changed it to handleError,
• Equality operator '==' invocation with references of unrelated types _warning_ on:
  
  
  
  • 'await' applied to 'Stream<BluetoothState>', which is not a 'Future'.,
  
  
  • btState == BluetoothState.unavailable,
  
  
  • btState != BluetoothState.on and
  
  
  • await flutterBlue.state != BluetoothState.on
  
  

@pauldemarco if it's BluetoothState.unavaiable then wouldn't it be neat to have BluetoothState.available instead of BluetoothState.on, cause on happens to be a reserved word?

I'm new to flutter and would appreciate all help.