Develop Reference

signalr android (kotlin) cannot connect to server because it is always DISCONNECTED

I use implementation 'com.microsoft.signalr:signalr:6.0.8' for android (kotlin) and backend is .Net 6
but the emulator cannot connect to the server (localhost). I try to code a function to check hubConnection.connectionState, it is DISCONNECTED.
no error happened. Can anyone guide me to find the error, here is the code:
import com.microsoft.signalr.Action1
import com.microsoft.signalr.HubConnection
import com.microsoft.signalr.HubConnectionBuilder
import com.microsoft.signalr.HubConnectionState
import io.reactivex.rxjava3.core.Single
import org.slf4j.Logger
import org.slf4j.LoggerFactory
class SignalRListener private constructor(){
private var hubConnection: HubConnection
private var logger: Logger
init {
logger = LoggerFactory.getLogger(HubConnection::class.java)
// define in constructor
hubConnection = HubConnectionBuilder.create("http://10.0.2.2:5291/hubs/presence")
.withAccessTokenProvider(Single.defer { Single.just("${Constanst.TOKEN}") })
.build()
hubConnection.on("UserIsOnline",
Action1 { member: Member -> println(member.DisplayName + "online") },
Member::class.java
)
hubConnection.on("UserIsOffline",
Action1 { username: String -> println(username+" offline") },
String::class.java
)
hubConnection.on(
"GetOnlineUsers",
Action1 { usersOnline : List<Member> ->
for (item in usersOnline) {
println(item.DisplayName)
}
},
List::class.java
)
hubConnection.start().doOnError({ logger.info("Client connected error.") })
}
private object Holder { val INSTANCE = SignalRListener() }
companion object {
#JvmStatic
fun getInstance(): SignalRListener{
return Holder.INSTANCE
}
}
fun stopHubConnection(){
if(hubConnection.connectionState == HubConnectionState.CONNECTED){
hubConnection.stop()
}
}
fun getConnectionState(){
println(hubConnection.connectionState.toString())
}
fun log(){
logger.info("Debug infor siganlR {}", hubConnection.connectionId)
}
}
Web (React) runs well with the backend.
class MainActivity : AppCompatActivity() {
lateinit var signalR: SignalRListener;
var btnCheck: Button? = null
var btnLog: Button? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
signalR = SignalRListener.getInstance()
btnCheck = findViewById(R.id.btnCheck)
btnCheck?.setOnClickListener {
signalR.getConnectionState()
}
btnLog = findViewById(R.id.btnLog)
btnLog?.setOnClickListener {
signalR.log()
}
}
}

As you are in the android emulator, You have to access your localhost so that it reaches your server. If you need internet through proxy you can also set it from the Settings and Proxy and there you can define your proxy settings.

I fixed the problem with the following:
in BE(.Net Core) remove this line:
app.UseHttpsRedirection();
and the client calls http not https:
hubConnection = HubConnectionBuilder.create("http://10.0.2.2:5291/hubs/presence")
hubConnection.start().blockingAwait()
It worked fine

NFC P2P with PN532 module on Arduino and Android Kotlin

I am trying to send a string message from Android to Arduino with the PN532 module. When I approach the smartphone (with the app open) to the module, the "tap to beam" UI shows up, but after I tap on the screen, the phone tells me to approach the two devices again. After I approach them again (with the "approach the devices again" message still displayed on the screen), nothing happens and arduino prints out "failed".
Here is the Kotlin code:
package com.cerowski.nfcclient
import android.nfc.NdefMessage
import android.nfc.NdefRecord
import android.nfc.NfcAdapter
import android.os.Bundle
import android.widget.TextView
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.viewpager.widget.ViewPager
import com.cerowski.nfcclient.databinding.ActivityMainBinding
import com.cerowski.nfcclient.ui.main.SectionsPagerAdapter
import com.google.android.material.floatingactionbutton.FloatingActionButton
import com.google.android.material.snackbar.Snackbar
import com.google.android.material.tabs.TabLayout
import java.io.File
import java.io.UnsupportedEncodingException
class MainActivity : AppCompatActivity() {
private lateinit var binding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {config(); sendid();
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
val sectionsPagerAdapter = SectionsPagerAdapter(this, supportFragmentManager)
val viewPager: ViewPager = binding.viewPager
viewPager.adapter = sectionsPagerAdapter
val tabs: TabLayout = binding.tabs
tabs.setupWithViewPager(viewPager)
val fab: FloatingActionButton = binding.fab
fab.setOnClickListener { view ->
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show()
}
}
fun config(){
val dir = getExternalFilesDir(null);
val file = File(dir,"config");
var msgtext="";
val msg = TextView (this)
if (dir!=null) {
if (!file.exists()) {msgtext = "config not found, attempting to create..."; file.createNewFile(); if(file.exists()) {msgtext = "config created successfully"; file.writeText(idgenerator())} else {msgtext = "problem creating file"}}
else {msgtext = (file.readText())}
} else {msgtext = "app directory not found"}
}
fun idgenerator() : String {
val allowedChars = ('a'..'z') + ('A'..'Z') + ('0'..'9')
return (1..16)
.map { allowedChars.random() }
.joinToString("")
}
fun sendid() {
val dir = getExternalFilesDir(null);
val file = File(dir,"config");
//var bytes = file.readBytes();
//var nfcmsg = NdefMessage(bytes);
//var msgtext="";
var nfcAdapter = NfcAdapter.getDefaultAdapter(this);
if (nfcAdapter != null) {
val msg: String = file.readText().toString()
val languageCode: ByteArray
val msgBytes: ByteArray
try {
languageCode = "en".toByteArray(charset("US-ASCII"))
msgBytes = msg.toByteArray(charset("UTF-8"))
} catch (e: UnsupportedEncodingException) {
return
}
val messagePayload = ByteArray(
1 + languageCode.size
+ msgBytes.size
)
messagePayload[0] = 0x02.toByte() // status byte: UTF-8 encoding and
// length of language code is 2
// length of language code is 2
System.arraycopy(
languageCode, 0, messagePayload, 1,
languageCode.size
)
System.arraycopy(
msgBytes, 0, messagePayload, 1 + languageCode.size,
msgBytes.size
)
val message: NdefMessage
val records = arrayOfNulls<NdefRecord>(1)
val textRecord = NdefRecord(
NdefRecord.TNF_WELL_KNOWN,
NdefRecord.RTD_TEXT, byteArrayOf(), messagePayload
)
records[0] = textRecord
message = NdefMessage(records)
nfcAdapter.setNdefPushMessage(message, this);
}
else {Toast.makeText(this, "NFC is not available", Toast.LENGTH_LONG).show();}
}
}
And here is the code for my Arduino Uno with the PN532 module (the red one, if you search for photos online):
// Receive a NDEF message from a Peer
// Requires SPI. Tested with Seeed Studio NFC Shield v2
#include "SPI.h"
#include "PN532_SPI.h"
#include "snep.h"
#include "NdefMessage.h"
PN532_SPI pn532spi(SPI, 10);
SNEP nfc(pn532spi);
uint8_t ndefBuf[128];
void setup() {
Serial.begin(9600);
Serial.println("NFC Peer to Peer Example - Receive Message");
}
void loop() {
Serial.println("Waiting for message from Peer");
int msgSize = nfc.read(ndefBuf, sizeof(ndefBuf));
if (msgSize > 0) {
NdefMessage msg = NdefMessage(ndefBuf, msgSize);
msg.print();
Serial.println("\nSuccess");
} else {
Serial.println("Failed");
}
delay(3000);
}
The little switches on the NFC module are in the right positions and the module is connected to the board as it should be (for SPI), So I do not know what is the thing that causes it to fail.
Any help is much appreciated.

First check if it's even a) available, b) enabled and c) register & implement the callbacks. In Java:
MainActivity extends AppCompatActivity implements
NfcAdapter.CreateNdefMessageCallback,
NfcAdapter.OnNdefPushCompleteCallback,
NfcAdapter.CreateBeamUrisCallback {
...
if (
Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1 &&
Build.VERSION.SDK_INT < Build.VERSION_CODES.Q
) {
NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);
if (!nfcAdapter.isEnabled()) {
startActivity(new Intent(Settings.ACTION_NFC_SETTINGS));
} else if (!nfcAdapter.isNdefPushEnabled()) {
startActivity(new Intent(Settings.ACTION_NFCSHARING_SETTINGS));
} else {
nfcAdapter.setNdefPushMessageCallback(this);
nfcAdapter.setOnNdefPushCompleteCallback(this);
nfcAdapter.setNdefPushMessage(nfcMessage, this);
}
}
Deprecated in Build.VERSION_CODES.Q means still available; maybe <=.
These callbacks might also provide you with more detail, why it even fails.
Else you'll send a NDEF message and it will not know what to do next ...
Alike this you might also be able to produce a proper error message.
Also see: https://developer.android.com/training/beam-files/send-files

Android BLE RxKotlin

I'm trying to create a BLE service that will scan for devices and using rxKotlin create an observable that will allow another class to observe when a device is found. I'm confused on how to create the observable that will allow another class to subscribe and tutorials are all over the place. Can someone give me a pointer on how to do so or a good tutorial.
Bluetoothservice class callback where devices are discovered
var foundDeviceObservable: Observable<BluetoothDevice> = Observable.create { }
private val scanCallback = object : ScanCallback() {
override fun onScanResult(callbackType: Int, result: ScanResult) {
with(result.device) {
var foundName = if (name == null) "N/A" else name
foundDevice = BluetoothDevice(
foundName,
address,
address,
result.device.type.toString()
)
foundDeviceObservable.subscribe {
//Update Observable value?
}
}
}
}
class DeviceListViewModel(application: Application) : AndroidViewModel(application) {
private val bluetoothService = BLEService()
//Where I am trying to do logic with device
fun getDeviceObservable(){
bluetoothService.getDeviceObservable().subscribe{ it ->
}
}
Solution
Was able to find the solution after reading user4097210's reply. Just had to change the found device to
var foundDeviceObservable: BehaviorSubject<BluetoothDevice> = BehaviorSubject.create()
and then call the next method in the callback
private val scanCallback = object : ScanCallback() {
override fun onScanResult(callbackType: Int, result: ScanResult) {
with(result.device) {
var foundName = if (name == null) "N/A" else name
foundDevice = BluetoothDevice(
foundName,
address,
address,
result.device.type.toString()
)
foundDeviceObservable.onNext(foundDevice)
}
}
}

use BehaviorSubject
// create a BehaviorSubject
var foundDeviceObservable: BehaviorSubject<BluetoothDevice> = BehaviorSubject()
// call onNext() to send new found device
foundDeviceObservable.onNext(foundDevice)
// do your logic use foundDeviceObservable
foundDeviceObservable.subscribe(...)

Data received from Android Bluetooth socket is getting plotted in the line chart only after socket's termination

I have recently started working on Android, Kotlin and MPAndroidChart. I am developing an Android application that receives data from a bluetooth server and the data obtained should be plotted in real time using MPAndroidChart.
Here is the Kotlin code:
package com.example.flowsensor
import ...
class ConnectionActivity:AppCompatActivity() {
companion object{
val TAG = "FlowSensor"
val APP_NAME = "FlowSensor"
var myUUID: UUID = UUID.fromString("8ce255c0-200a-11e0-ac64-0800200c9a66")
var mBluetoothSocket: BluetoothSocket? = null
lateinit var mProgress: ProgressDialog
lateinit var mBluetoothAdapter: BluetoothAdapter
var mIsConnected: Boolean = false
lateinit var mAddress: String
lateinit var editText:EditText
lateinit var mChart:LineChart
var xVal:Int = 0
var yVal:Int = 0
}
override fun onCreate(savedInstanceState: Bundle?) {
requestedOrientation = ActivityInfo.SCREEN_ORIENTATION_PORTRAIT
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_connection)
mChart = findViewById<LineChart>(R.id.line_chart)
receive_button.setOnClickListener{
ReceiveData()
}
}
//1 parameters missing
private fun mAddEntry() {
Log.d(TAG, "yVal : $yVal")
var mData = mChart.data
if(mData != null){
var mDataSet = mData.getDataSetByIndex(0)
if(mDataSet == null){
mDataSet = createDataSet()
mData.addDataSet(mDataSet)
}
var mEntry:Entry = Entry( xVal.toFloat(), yVal.toFloat())
xVal++
mData.addEntry(mEntry, 0)
//Notify chart data has changed
mChart.notifyDataSetChanged()
//Limit no of visible entries
// mChart.setVisibleXRange(1f, 6f)
mChart.setVisibleXRangeMaximum(6f)
//Scroll to the last entry
mChart.moveViewToX(xVal.toFloat())
}
}
//1 parameter missing
private fun createDataSet(): LineDataSet? {
var mDataSet = LineDataSet(null, "Data vals")
//mDataSet.setDrawCubic
mDataSet.cubicIntensity = 0.2f
mDataSet.axisDependency = YAxis.AxisDependency.LEFT
mDataSet.setColor(ColorTemplate.getHoloBlue())
mDataSet.setCircleColor(ColorTemplate.getHoloBlue())
mDataSet.lineWidth = 2f
mDataSet.circleSize = 4f
mDataSet.fillAlpha = 65
mDataSet.fillColor = ColorTemplate.getHoloBlue()
mDataSet.highLightColor = Color.rgb(244, 117, 177)
mDataSet.valueTextColor = Color.WHITE
mDataSet.valueTextSize = 10f
return mDataSet
}
private fun ReceiveData() {
val buffer = ByteArray(1024) // buffer store for the stream
var bytes: Int // bytes returned from read()
// Keep listening to the InputStream until an exception occurs
Log.d(TAG, "Inside ReceiveData()")
while (true) { // Read from the InputStream
if(mBluetoothSocket != null)
{
try {
bytes = mBluetoothSocket!!.inputStream.read(buffer)
val incomingMessage = String(buffer, 0, bytes)
Log.d(TAG, "InputStream: $incomingMessage")
yVal = incomingMessage.toInt()
mAddEntry()
} catch (e: IOException) {
Log.e(TAG, "write: Error reading Input Stream. " + e.message)
break
}
}
}
}
}
Here is the logcat log logged in verbose mode.
App starts in the Main Activity(code not attached here), looks for paired devices then using
val intent = Intent(this, ConnectionActivity::class.java)
intent.putExtra(EXTRA_ADDRESS, address)
startActivity(intent) code, control reaches Connection Activity (code attached above).
App is successfully receiving data from server; verified by observing logcat. In ReceiveData(), I am trying to pass the received data to mAddEntry() which is responsible for drawing the graph. But the problem is, data is plotted only after I terminate the socket, so after Line no 112 in the attached logcat log, all the data is plotted at once (no data loss). I want to plot data in real time, and this is the problem I am facing.
Note: graph plotting has been independently verified by passing dummy data in real-time inside onCreate() in ConnectionActivity class using the timer.scheduleAtFixedRate. This is working as expected.

by calling the reciveData() inside the receive_button onClickListner you are executing while loop that will run until Bluetooth socket is connected and it is runing on the MainThread (UIThread) and it will block the UI thread and doesn't let any other ui updateto happen you should execute the reciveData() function on the background and when you want the plot the data in chart you should pass the data in ui thread or call the mAddEntry() function in ui thread

RxAndroidBLE do not find devices on android 4.3

Hello I'm using RxAndroidBLE to detect a BLE device. On android 6 >= everything seems to work okay but not on a 4.3 device.
My app can only discover the desirable BLE device only once at start. After the device has been discovered no more new discoveries at all until I restart the app. Any advice would be highly appreciated.
Below minimum (not)working code example:
MainActivity
import android.content.Context
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.os.Handler
import android.util.Log
import com.polidea.rxandroidble.RxBleClient
import com.polidea.rxandroidble.exceptions.BleScanException
import com.polidea.rxandroidble.scan.ScanResult
import com.polidea.rxandroidble.scan.ScanSettings
import rx.Subscription
import rx.android.schedulers.AndroidSchedulers
import java.util.*
import java.util.concurrent.Executors
import java.util.concurrent.TimeUnit
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
startLeScan(applicationContext)
}
private var rxBleClient: RxBleClient? = null
private var scanSubscription: Subscription? = null
private var handler: Handler? = null
private var timer: Timer? = null
private var timerTask: TimerTask? = null
private var delay: Int = 0
private fun isScanning(): Boolean {
return scanSubscription != null
}
fun startLeScan(context: Context) {
rxBleClient = MyaPP.getRxBleClient(context)
if (isScanning()) {
scanSubscription?.unsubscribe()
} else {
scanSubscription = rxBleClient?.scanBleDevices(
com.polidea.rxandroidble.scan.ScanSettings.Builder()
.setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
.setCallbackType(ScanSettings.CALLBACK_TYPE_ALL_MATCHES)
.build())
?.observeOn(AndroidSchedulers.mainThread())
//?.doOnNext(this::newDevicesFound)
?.doOnUnsubscribe(this::clearSubscription)
?.subscribe(this::newDevicesFound, this::onScanFailure)
}
if(handler == null) {
handler = Handler()
timer = Timer(false)
timerTask = object : TimerTask() {
override fun run() {
handler?.post {
if (delay > 7) {
delay = 0
val service = Executors.newSingleThreadExecutor()
service.submit(Runnable {
//startLeScan(context)
})
} else {
delay = delay + 1
}
}
}
}
timer?.scheduleAtFixedRate(timerTask, 0, 300)
}
}
private fun newDevicesFound(devices: ScanResult) {
Log.d("WHYY??", devices.bleDevice.name)
}
fun stopScan() {
scanSubscription?.unsubscribe()
destroy()
}
private fun clearSubscription() {
scanSubscription = null
}
private fun onScanFailure(throwable: Throwable) {
if (throwable is BleScanException) {
handleBleScanException(throwable)
}
}
private fun handleBleScanException(bleScanException: BleScanException) {
val text: String
when (bleScanException.reason) {
BleScanException.BLUETOOTH_NOT_AVAILABLE -> text = "Bluetooth is not available"
BleScanException.BLUETOOTH_DISABLED -> text = "Enable bluetooth and try again"
BleScanException.LOCATION_PERMISSION_MISSING -> text = "On Android 6.0 location permission is required. Implement Runtime Permissions"
BleScanException.LOCATION_SERVICES_DISABLED -> text = "Location services needs to be enabled on Android 6.0"
BleScanException.SCAN_FAILED_ALREADY_STARTED -> text = "Scan with the same filters is already started"
BleScanException.SCAN_FAILED_APPLICATION_REGISTRATION_FAILED -> text = "Failed to register application for bluetooth scan"
BleScanException.SCAN_FAILED_FEATURE_UNSUPPORTED -> text = "Scan with specified parameters is not supported"
BleScanException.SCAN_FAILED_INTERNAL_ERROR -> text = "Scan failed due to internal error"
BleScanException.SCAN_FAILED_OUT_OF_HARDWARE_RESOURCES -> text = "Scan cannot start due to limited hardware resources"
BleScanException.UNDOCUMENTED_SCAN_THROTTLE -> text = String.format(
Locale.getDefault(),
"Android 7+ does not allow more scans. Try in %d seconds",
secondsTill(bleScanException.retryDateSuggestion)
)
BleScanException.UNKNOWN_ERROR_CODE, BleScanException.BLUETOOTH_CANNOT_START -> text = "Unable to start scanning"
else -> text = "Unable to start scanning"
}
Log.w("EXCEPTION", text, bleScanException)
}
private fun secondsTill(retryDateSuggestion: Date?): Long {
if (retryDateSuggestion != null) {
return TimeUnit.MILLISECONDS.toSeconds(retryDateSuggestion.time - System.currentTimeMillis())
}
return 0
}
private fun destroy() {
timer?.cancel()
handler?.removeCallbacks(timerTask)
handler = null
timerTask = null
timer = null
}
}
MyaPP
import android.app.Application
import android.content.Context
import com.polidea.rxandroidble.RxBleClient
import com.polidea.rxandroidble.internal.RxBleLog
class MyaPP: Application() {
private var rxBleClient: RxBleClient? = null
companion object {
fun getRxBleClient(context: Context): RxBleClient? {
val application = context.applicationContext as MyaPP
return application.rxBleClient
}
}
override fun onCreate() {
super.onCreate()
rxBleClient = RxBleClient.create(this)
RxBleClient.setLogLevel(RxBleLog.DEBUG)
}
}
build.gradle
compile "com.polidea.rxandroidble:rxandroidble:1.5.0"
implementation 'io.reactivex:rxandroid:1.2.1'
manifest
<application
android:name=".MyaPP"

Your code looks a lot like the library's sample app (version 1.5.0, branch master-rxjava1). I have checked that recently on Android 4.4.4 which is the oldest I have and it worked fine. There were no API changes between 4.3 and 4.4.
What you may be experiencing is a behaviour specific to your device (feel free to share your phone model) in which it only callbacks for the first time it scans a particular peripheral. There are some threads about this topic already like this one.