Bluetooth Socket OutputStream NullPointerException when calling Write()

Question

I have a strange issue where apparently my outputstream is null even though I have multiple checks and have used the debugger to confirm it is not null. So the code in question:

 @Override
protected void onHandleIntent(Intent intent) {
    device = (BluetoothDevice) intent.getExtras().get("device");

    if (device != null) {
        Log.v("DeviceManager", "Beginning attempts to communicate to: " + device.getName());
        try {
            BluetoothSocket socket = device.createRfcommSocketToServiceRecord(device.getUuids()[0].getUuid());
            outputStream = socket.getOutputStream();
            inputStream = socket.getInputStream();

            while (Utils.appIsInForeground && device != null) {
                if (outputStream == null){
                    Log.e("DeviceManager", "Looks like the outputStream is null...");
                    if (inputStream == null){
                        Log.e("DeviceManager", "And input stream is null, are you even connected to the device?");
                    }else{
                        Log.e("DeviceManager", "Although strangely, input stream has been set.");
                    }
                }else{
                    String myString = "This is a string!";
                    byte[] myByteArray = myString.getBytes("UTF-8");
                    //Crashes here:
                    outputStream.write(myByteArray);
                }
                Thread.sleep(1000);
            }

        } catch (IOException e) {
            e.printStackTrace();
            Log.e("DeviceManager", "Can't create a socket to the bluetooth device.");
        } catch (InterruptedException e) {
            e.printStackTrace();
            Log.e("DeviceManager", "The sleep thread was interrupted.");
        } catch (NullPointerException e) {
            e.printStackTrace();
            Log.e("DeviceManager", "A null pointer exception, this is probably not good.");
        }
    }else {
        Log.e("DeviceManager", "The Device Manager has been passed a null object instead of a device.");
    }
}

The stack trace is as follows:

03-23 15:55:12.134 3042-3171/com.name.app W/System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.OutputStream.write(byte[], int, int)' on a null object reference
03-23 15:55:12.135 3042-3171/com.name.app W/System.err:     at android.bluetooth.BluetoothSocket.write(BluetoothSocket.java:553)
03-23 15:55:12.136 3042-3171/com.name.app W/System.err:     at android.bluetooth.BluetoothOutputStream.write(BluetoothOutputStream.java:85)
03-23 15:55:12.136 3042-3171/com.name.app W/System.err:     at java.io.OutputStream.write(OutputStream.java:75)
03-23 15:55:12.137 3042-3171/com.name.app W/System.err:     at com.name.app.service.DeviceManager.onHandleIntent(DeviceManager.java:73)
03-23 15:55:12.138 3042-3171/com.name.app W/System.err:     at android.app.IntentService$ServiceHandler.handleMessage(IntentService.java:67)
03-23 15:55:12.138 3042-3171/com.name.app W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:102)
03-23 15:55:12.139 3042-3171/com.name.app W/System.err:     at android.os.Looper.loop(Looper.java:154)
03-23 15:55:12.139 3042-3171/com.name.app W/System.err:     at android.os.HandlerThread.run(HandlerThread.java:61)

This what the debugger thinks of each of the variables:

myByteArray = {byte[17]@4799} 
this = {DeviceManager@4698} 
intent = {Intent@4705} "Intent { cmp=com.name.app/.service.DeviceManager (has extras) }"
socket = {BluetoothSocket@4706} 
myString = "This is a string!"
myByteArray = {byte[17]@4799} 
outputStream = {BluetoothOutputStream@4743} 

I'm utterly baffled at this point, nothing is null yet the error persists. I have also tried the following:

outputStream.write(myByteArray, 0, myByteArray.length);

It produces the exact same trace.

Answer 1

You need to call socket.connect() before using input/output stream. See my detailed answer https://stackoverflow.com/a/42570610/5664712