Carling Knight Carling Knight -4 years ago 221
Android Question

Bluetooth Socket OutputStream NullPointerException when calling Write()

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 Source

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

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