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String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，我抓住了这个

原因：java.lang.reflect.InvocationTargetException在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.Zygote $ MethodAndArgsCaller.run（Zygote.java:245）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:921）由以下原因引起：java.io.IOException：读取失败，套接字可能关闭或超时，读取ret：-1在android.bluetooth.BluetoothSocket.readAll（BluetoothSocket.java:706）在android.bluetooth.BluetoothSocket.readInt（BluetoothSocket.java:718）在android.bluetooth.BluetoothSocket.connect（BluetoothSocket.java:384）在com.example.nikita.vas.Validation.bluetoothAdd（Validation.kt：52）在com.example.nikita.vas.Validation.access $ bluetoothAdd（Validation.kt：21）在com.example.nikita.vas.Validation $ onCreate $ 1.onClick（Validation.kt：30）在android.view.View.performClick（View.java:6291）在android.view.View $ PerformClick.run（View.java:24931）在android.os.Handler.handleCallback（Handler.java:808）在android.os.Handler.dispatchMessage（Handler.java:101）在android.os.Looper.loop（Looper.java:166）

Answer 1

您在访问mmSocket.connect()对象之前忘了调用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)