I'm having a weird problem. I already lost a lot of time trying to understand and solve this but nothing works.
I have an app that communicates with another device across bluetooth connection to receive some sensor data. In that point, everything works fine, I can connect to the device, receive and treat the messages.
But yesterday, I decided to create some kind of log file to directly save in the internal memory the data received from the device without any kind of transformation from my app.
To receive the data from the device, I have a background thread:
public class CommunicationThread extends Thread {
private static final UUID UUID_DEVICE = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
private static final String TAG = CommunicationThread.class.getSimpleName();
private CommunicationListener mListener;
private boolean mRunning;
private BluetoothSocket mBluetoothSocket;
private InputStream mInputStream;
private OutputStream mOutputStream;
public interface CommunicationListener {
void onMessageReceived(String msg);
}
public CommunicationThread(
@NonNull BluetoothDevice device,
@Nullable CommunicationListener listener) throws IOException {
BluetoothSocket socket = device.createRfcommSocketToServiceRecord(UUID_DEVICE);
socket.connect();
this.mBluetoothSocket = socket;
this.mInputStream = socket.getInputStream();
this.mOutputStream = socket.getOutputStream();
this.mListener = listener;
}
@Override
public void run() {
mRunning = true;
byte[] bytes = new byte[1024];
int length;
while (mRunning) {
try {
Log.d(TAG, "Waiting for message");
// read the message (block until receive)
length = mInputStream.read(bytes);
String msg = new String(bytes, 0, length);
Log.d(TAG, "Message: " + msg);
// Message received, inform the listener
if (mListener != null)
mListener.onMessageReceived(msg);
} catch (Exception e) {
Log.e(TAG, "Error reading the message", e);
}
}
}
public void sendCommand(String msg) {
try {
mOutputStream.write((msg).getBytes());
} catch (Exception e) {
Log.e(TAG, "Error to send message", e);
}
}
public void stopCommunication() {
mRunning = false;
mListener = null;
try {
if (mBluetoothSocket != null) {
mBluetoothSocket.close();
}
if (mInputStream != null) {
mInputStream.close();
}
if (mOutputStream != null) {
mOutputStream.close();
}
} catch (IOException e) {
Log.e(TAG, "Error to stop communication", e);
}
}
}
This thread works pretty fine and when a message is received, it informs the listener, my Controller class. The first thing that I try to do when a message comes, is save it:
public class Controller implements CommunicationThread.CommunicationListener
...
@Override
public void onMessageReceived(final String msg) {
Log.d(TAG, "onMessageReceived(msg): " + msg);
mLogCreator.saveThis(msg);
....
}
}
Here is the LogCreator class:
public class LogCreator {
private static final String TAG = LogCreator.class.getSimpleName();
public static final String LOG_FILE_NAME = "log.txt";
private final Context mContext;
private volatile String mTempFullLog;
public LogCreator(Context context) {
mContext = context.getApplicationContext();
File dir = new File(mContext.getFilesDir(), "log_folder");
if (!dir.exists()) {
dir.mkdirs();
File file = new File(dir, LOG_FILE_NAME);
writeString(file, "");
Log.d(TAG, "empty file created");
}
}
public void saveThis(final String data) {
mTempFullLog += "\n" + data;
Log.d(TAG, "New log: " + data);
}
public void start() {
File dir = new File(mContext.getFilesDir(), "log_folder");
File file = new File(dir, LOG_FILE_NAME);
mTempFullLog = readString(file);
Log.d(TAG, "File: " + file);
Log.d(TAG, "Temp full log: " + mTempFullLog);
}
public void stop() {
File dir = new File(mContext.getFilesDir(), "log_folder");
File file = new File(dir, LOG_FILE_NAME);
writeString(file, mTempFullLog);
Log.d(TAG, "log saved: " + mTempFullLog);
}
}
The LogCreator class is already initialized and it works properly, because if I try to read the file later, everything is there.
The real problem is the following: there is a lot of calls to Log.d during this execution flow, and this makes very easy to me to understand the all process. But, the logs are only printed in the logcat until this Log.d call, in the CommunicationThread class:
Log.d(TAG, "Waiting for message);
After the message received, all code executes normally, but no logs are printed in the logcat and I really dont know why.
Logs not printed:
CommunicationThread:
Log.d(TAG, "Message: " + msg);
Controller:
Log.d(TAG, "onMessageReceived(msg): " + msg);
LogCreator:
Log.d(TAG, "New log: " + data);
Like I said, I know that everything is working fine with the code because the log file is created in internal memory even without the logcat prints. It cost me some hours to realize that the problem is only with the log and not really in my code.
For testing purpose, if I add this code in the saveThis method of LogCreator, it executes normally:
new Handler(Looper.getMainLooper()).post(new Runnable() {
@Override
public void run() {
Toast.makeText(mContext, data, Toast.LENGTH_SHORT).show();
}
});
This makes me think that everything could be a thread problem, because the start and stop methods of LogCreator are both called from the main thread not the CommunicationThread and both methods have their logs printed. Because of this, in the onMessageReceived method of the Controller class, I tried this:
new Handler(Looper.getMainLooper()).post(new Runnable() {
@Override
public void run() {
mLogCreator.saveThis(msg);
}
});
But, unfortunately, the logs don't get printed in the logcat. The toast is still executed and the data are still saved to the file.
If anyone has any idea of what might be causing this, I really want to know, thanks.
I finally find the solution myself. The reason why the following not work is not clear for me, and IMO it should be treated like a bug.
I compile the app in debug mode and discover that the string received from the device has a "\r" in the end.
Example: "15.50\r"
So, for some strange reason, if I try to do this:
Log.d(TAG, "New log: " + data);
Nothing prints and we don't receive no warnings at all.
But, if I do this instead:
Log.d(TAG, "New log: " + data.replace("\r", ""));
Where data is: "15.50\r"
Everything works and the logcat prints the message.