android - arduino和android之间通过蓝牙进行数据传输。 NPE问题

Question

我应该将一些琴弦传送到arduino。只是通过而已，什么也不要。
这是我的代码。我是第一次使用android和kotlin。

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))

            }
        }
    }
}

}

现在，当我添加mmSocket !!。connect()时，我就明白了

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)

Answer 1

在访问mmSocket.connect()对象之前，您忘记了调用outputStream。
试试这个:

 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)