Develop Reference

Flutter/Dart: Bad State errors when trying to close down a stream pipeline

I'm building a mobile app in flutter which pipes the mic audio (mic_stream lib) to a websocket. I’m really struggling to close down the stream pipeline when I'm done with it. I’m getting various “Bad State” exceptions such as Cannot add event while adding a stream. The particulars depend on how I set up the pipeline but it seems to be at the root because the returned addStream future never completes. Any ideas what would cause that?
As said above, the source stream is from the mic_stream lib which pulls from native via Flutter's EventChannel.receiveBroadcastStream. The docs for this method says its returned stream will only close down when there are no more listeners. I try closing my websocket and get a similar error for the same reason (websocket internal bad state b/c addStream never completes). I'm tried wrapping the mic stream in a StreamController and closing that but I get the error mentioned above.
Starting to feel like it's a bug. Maybe EventChannel's stream is special? Or is it related to it being a "broadcast" stream.
Feeling stuck. Any help appreciated...thx

Flutter makes this a little confusing by returning a stream from EventChannel that you can't really use in the normal pipeline chaining way if you ever need to close it. Perhaps they should have done internally what I'm about to show as the workaround.
First for clarity, when you use addStream on StreamController (StreamConsumer rather) it blocks you from "manual" control via the add() method and also the close() until that stream completes. This makes sense, if you think about it, since the source stream should determine when it closes. That's why addStream() returns a Future – so you know when you can resume using those methods, or add another stream. Doing so beforehand will trigger the Bad State errors mentioned above.
From the docs for EventChannel::receiveBroadcastStream()...
Stream activation happens only when stream listener count changes from 0 to 1. Stream deactivation happens only when stream listener count changes from 1 to 0.
So we need to decide when it is done, and to do this we need to control its subscription rather than bury it in a pipeline or a StreamController's private internals via the addStream() method. So instead we'll listen to it directly, capturing the subscription to close when we're done. Then we just proxy the data into a StreamController or pipeline manually via add()
Stream<Uint8List> micStream = await MicStream.microphone(
sampleRate: AUDIO_SAMPLE_RATE,
channelConfig: ChannelConfig.CHANNEL_IN_MONO,
audioFormat: AudioFormat.ENCODING_PCM_16BIT);//,
// audioSource: AudioSource.MIC); // ios only supports default at the mo'
StreamController? s;
// We need to control the listener subscription
// so we can end this stream as per the docs instructions
final micListener = micStream.listen((event) {
print('emitting...');
// Feed the streamcon manually
s!.add(event);
});
s= StreamController();
// Let the SCon's close() trigger the Listener's cancel()
s!.onCancel = () {
print("onCancel");
micListener.cancel();
};
s!.done.whenComplete(() {
print("done");
});
// Further consumers will use the _StreamCon's_ stream,
// _not_ the micStream above
s!.stream.listen((event) => print("listening..."));
// Now we can close the StreamController when we are done.
Future.delayed(Duration(seconds: 3), () {
s!.close();
});

I am trying to make an application that will make phone calls one after another from the list of number

I am developing an application for my friend who is in sales, this application will make phone calls one after another, as soon as one phone call gets disconnected, it will automatically make call to another number from the list. This list can be read from and xml data source or json or mongodb or even from excel sheet.
This could be an ios app that reads data from an end point and stores them and can initiate the call at any point and it wont stop until all the calls are made.
Next call will be made only after the first call has been finished.
I am thinking about using node based web app using google voice to trigger the chain.
I've no experience with ios / android apis but Im willing to work on that if it's a viable thing on that platform.
Note: what we're trying to avoid is whole process of
looking up the phone number.
touch hangup and then click for another phone number.
It should self trigger the next call as soon as current call gets disconnected.
Also we're trying to avoid any paid services like twillo.
Thanks in advance :)

for IOS, you could use CTCallCenter
self.callCenter = [[CTCallCenter alloc] init];
self.callCenter.callEventHandler = ^(CTCall *call){
if ([call.callState isEqualToString: CTCallStateConnected])
{
//NSLog(#"call stopped");
}
else if ([call.callState isEqualToString: CTCallStateDialing])
{
}
else if ([call.callState isEqualToString: CTCallStateDisconnected])
{
//NSLog(#"call played");
}
else if ([call.callState isEqualToString: CTCallStateIncoming])
{
}
};
Download phone list, loop inside phone list, make a call, listening for CTCallCenter and appdelegate's Event, detect user have finish last call, our app active again, then make the next call.
Or you can try in Demo here !

Android: here.com's getMapPackages listener never catches onGetMapPackagesComplete event

Using here.com proprietary code I'm trying to get the list of map packages so that I'll hopefuly know a country ID I'm interested in so I'm using the following code to load all map packages:
MapLoader mapLoader = MapLoader.getInstance();
mapLoader.addListener(mapLoaderListener);
boolean packagesgotten=mapLoader.getMapPackages();
Now the maploaderlistener is supposed to catch the event when this download is complete. So I put some code to output the packages in the onGetMapPackagesComplete method of the listener but it never gets called. No error, nothing. This code is in an AsyncTask as network requests require that.

App using Mobile Android GNSK crashes when identifyAlbumAsync() is called before audioProcessStart()

I have being upgrading an application to use the new Mobile Android GNSK but I have noticed that using the new MusicID-Stream is a little bit tricky. If the "identifyAlbumAsync" method get executed before the "audioProcessStart" method(since this need to be executed in a different thread), the application just crashes. In the Gracenote Demo application, the "audioProcessStart" method is continuously running so there is no need to synchronize its execution with the "identifyAlbumAsync" method call. Is it the way it is supposed to be used? It will be convenient if the application didn't crashed at least when the methods are not executed in order. Also in our application, we don't want to have the "audioProcessStart" method continuously like it is done in the demo application. We only want to run the "audioProcessStart" method when the user request identification and when the song playing gets identified , we want to stop the audio processing by calling "audioProcessStop". Is there an easy way to do this? Right now, we are getting the Thread where "identifyAlbumAsync" is running to sleep for 2 seconds in order to make sure that the Thread where the "audioProcessStart" method is supposed to run has time to get executed. Thank you in advance for your prompt response

In the upcoming 1.2 release, IGnMusicIdStreamEvents includes a callback that signals audio-processing has started, and an ID can be synced with this, e.g.:
#Override
public void musicIdStreamProcessingStatusEvent( GnMusicIdStreamProcessingStatus status, IGnCancellable canceller ) {
if (GnMusicIdStreamProcessingStatus.kStatusProcessingAudioStarted.compareTo(status) == 0) {
try {
gnMusicIdStream.identifyAlbumAsync();
} catch (GnException e) { }
}
}

Thanks for the feedback, you're right about this issue. Unfortunately right now sleeping is the best solution. But we are adding support for an explicit sync event in an upcoming release, please stay tuned.

how to implement pooling using android bluetooth chat sample app?

I am working on an application that uses BluetoothChat sample application.
In my main activity I am using a webview in which I load an external page. I am handling Bluetooth functionality via a javascript that loads with the external page. Basically I add a bridge between Javascript and native code via the following line:
myWebView.addJavascriptInterface(new WebAppInterface(this,myWebView), "Android");//I pass a refference to the context and a refference to the webview.
WebAppInterface is the class that has all the public methods I can call from Javascript. In this class I have methods like: enableBluetooth, disableBluetooth, listBoundedDevices, connect etc.
I am using BluetoothSerialService class from BluetoothChat sample application. My device has to connect to an embedded device which receives commands and answers back differently depending on the input I give. An example would be like: when I press a button on the webview I call the following native code:
while(true){
out.write(requestKey);//send command - where "out" is the OutputStream
key = in.read();//get response - where "in" is the InputStream
if(key==KEY1){
out.write(activateRFID);//send command - activateRFID
rfidTag = in.read();//get response - RFID Tag
updateUI(rfidTag);//perform function - update the UI with the tag
}
else if(key==KEY2){
out.write(deactivateRFID);//send command - deactivate RFID
response = in.read();//get response
}
else if(key==KEY3){
out.write(anotherCommand);//send command -
response = in.read();//get response
}
}
What I am trying to achieve is sending commands to another device(request the pressed key) and perform functions. This has to happen always (pooling the device for the key pressed and perform a particular function).
How can I start 1 SINGLE THREAD that pools the device (write to the OutputStream and read the response from the InputStream)? The BluetoothChat sample application works a little different: whenever I call BluetoothChatSevice.write() I get a response via ConnectedThread run method that sends messages to UI via a mHandler.
All suggestions are welcome.

I did it today. I suggest that you do a boolean function readWrite() that whenever you write to outputStream you also read from the inputStream and send the readBuffer to UI with mHandler. If both read and write are ok, than return true, if one of them went wrong than return false and use resetConection before closing your ConnectedThread. See my answer here for the resetConnection. Application using bluetooth SPP profile not working after update from Android 4.2 to Android 4.3
But the answer about pooling is the following:
In the ConnectedThread run() method do a while(true), call a method similar to readWrite(byte[] data) inside the loop, where in the first place you write something to the device, and then you read the data from the input stream (from the device). In this readWrite() method, if writing to outpustream went fine, then continue to read from the inputstream. if you got any data to the input stream, send the data to UI for processing with the mHandler (or do some processing before sending to the UI).
It worked very nice for me.