Data transmission between arduino and android over bluetooth. Problem with NPE

Question

I should transfer some Strings to arduino. Just only pass, do not take anything. This my code. I'm working with android and kotlin for the first time.

class Validation : AppCompatActivity() {
lateinit var mmOutputStream: OutputStream
lateinit var mmSocket: BluetoothSocket

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_validation)


    resolve_Btn.setOnClickListener {bluetoothAdd() }


}

@SuppressLint("HardwareIds")
private fun bluetoothAdd() {
    val mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter()
    if (mBluetoothAdapter == null) {
        // Device does not support Bluetooth

        Log.e("Bluetooth ", "not found")
    }

    if (mBluetoothAdapter!!.isEnabled) {
        val pairedDevices = mBluetoothAdapter.bondedDevices
        // If there are paired devices
        if (pairedDevices.size > 0) {
            // Loop through paired devices
            for (device in pairedDevices) {
                mmSocket= device.createRfcommSocketToServiceRecord(
                        UUID.fromString("00000000-0000-1000-8000-00805F9B34FB"))
                mmSocket.connect()
                mmOutputStream = mmSocket.outputStream
                val message = "aaa"
                val msgBuffer = message.toByteArray(Charset.defaultCharset())
                mmOutputStream.write(msgBuffer)
                Log.e("Mac Addressess", "are:  " + mBluetoothAdapter.getRemoteDevice(device.address))

            }
        }
    }
}

}

Now when I added mmSocket!!.connect(), I catch this

Caused by: java.lang.reflect.InvocationTargetException at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921) Caused by: java.io.IOException: read failed, socket might closed or timeout, read ret: -1 at android.bluetooth.BluetoothSocket.readAll(BluetoothSocket.java:706) at android.bluetooth.BluetoothSocket.readInt(BluetoothSocket.java:718) at android.bluetooth.BluetoothSocket.connect(BluetoothSocket.java:384) at com.example.nikita.vas.Validation.bluetoothAdd(Validation.kt:52) at com.example.nikita.vas.Validation.access$bluetoothAdd(Validation.kt:21) at com.example.nikita.vas.Validation$onCreate$1.onClick(Validation.kt:30) at android.view.View.performClick(View.java:6291) at android.view.View$PerformClick.run(View.java:24931) at android.os.Handler.handleCallback(Handler.java:808) at android.os.Handler.dispatchMessage(Handler.java:101) at android.os.Looper.loop(Looper.java:166)

score 3 · Accepted Answer · answered Nov 12 '18 at 10:49

3

You forgot to call mmSocket.connect() before accessing outputStream object. Try this:

 mmSocket= device.createRfcommSocketToServiceRecord( 
                    UUID.fromString("00000000-0000-1000-8000-00805F9B34FB"))
                    mmSocket.connect()
                    mmOutputStream = mmSocket!!.outputStream
                    val message = "aaa"
                    val msgBuffer = message.toByteArray(Charset.defaultCharset())
                    mmOutputStream!!.write(msgBuffer)

answered Nov 12 '18 at 10:49

Onix

662
3
10

Thank you very much – Nikitich Nov 12 '18 at 12:25
But now I have another problem: java.lang.RuntimeException: java.lang.reflect.InvocationTargetException at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921) When i try call mmSocket!!.connect() – Nikitich Nov 12 '18 at 12:57
In the log of error must seen line cause error in you code. Please attach full stack-trace here. – Onix Nov 12 '18 at 13:30
I looked at your stacktrace. Look there, maybe this is answer https://stackoverflow.com/questions/18657427/ioexception-read-failed-socket-might-closed-bluetooth-on-android-4-3 – Onix Nov 13 '18 at 07:02

Data transmission between arduino and android over bluetooth. Problem with NPE

1 Answers1