CODEWITHSUNDEEP
androidbluetoothinputstream
hes_theman
hes_theman

Reputation: 628

Error in reading data from InputStream in Bluetooth on Android

I'm working on an Android app, which uses bluetooth connection to transfer data between my android smartphone and a non-android bluetooth module, using SPP profile. I've used Bluetooth Chat Example from Android Developer site as reference.

I've successfully made two devices connect to each other and sent simple strings from the smart phone to the bluetooth module. But I've got some error in reading data sent back from the module. I've used the following code, which is exactly the same as in Bluetooth Chat Example, to read data from InputStream

while (true) {
    try {
        // Read from the InputStream
        bytes = mmInStream.read(buffer);
        String str = new String(buffer);
        Log.i(TAG, "mmInStream - " + str);
        // Send the obtained bytes to the UI Activity
        mHandler.obtainMessage(BluetoothChat.MESSAGE_READ, bytes, -1, buffer)
                .sendToTarget();
    } catch (IOException e) {
        Log.e(TAG, "disconnected", e);
        connectionLost();
        break;
    }
}

When my bluetooth module send a simple string to the phone, that string is not received correctly. It is splited into several pieces in random ways. For example, if I send "1234567890abcdef1234567890abcdef0123456789" for three times to the phone, the Logcat on Eclipse will log these:

mmInstream - 12345678910abcdef��������(continuing null)
mmInstream - 1��������(continuing null)
mmInstream - 2345678910abcdef0123456789��������(continuing null)

for the first time. In the second and the third time data is transmitted, it is received in a difference pieces:

mmInstream - 1234567891�������(continuing null)
mmInstream - 0abcdef012�������(continuing null)
mmInstream - 3456789���������(continuing null)

mmInstream - 1234567891����������������(continuing null)
mmInstream - 0abcdef0123456789������������(continuing null)

I don't know why this happen and how to solve this problem. If data is received in a arbitrary way like this, I can't get necessary data to process. How can I get it in one pieces?

Any help would be appreciated.

Many Thanks.

Upvotes: 17

Views: 24724

Answers (9)

ROSGIFTS
ROSGIFTS

Reputation: 1

I looked for solving of this problem. And found it: It's a bad idea to send buffer which could be reload. So i did this: ( i send not the buffer but cloned RXbuffer)

Now I have 0 errors for 1000 blocks (for 32 bytes each) instead 20% errors before;

  public void run() {
        Log.i(TAG, "BEGIN mConnectedThread");
        byte[] buffer = new byte[1024];
        byte[] bufferRX = new byte[1024];
        int bytes;

        // Keep listening to the InputStream while connected
        while (mState == STATE_CONNECTED) {
            try {
                // Read from the InputStream
                bytes = mmInStream.read(buffer);
                bufferRX = buffer.clone();
                
                // Send the obtained bytes to the UI Activity
                mHandler.obtainMessage(Constants.MESSAGE_READ, bytes, -1, bufferRX)
                        .sendToTarget();
            } catch (IOException e) {
                Log.e(TAG, "disconnected", e);
                connectionLost();
                break;
            }
        }
    }

Upvotes: 0

mea.samir
mea.samir

Reputation: 33

I have used last two codes, they work well, though when connection is lost user interface does not get notified and so state does not change to STATE_NONE. In my case I want app to try to reconnect last device whenever connection is lost!! after trying many ways I finally solved the problem this way:

  1. I created an END character, this character I know I will never use but just in the end of string I am sending. "." is my end of string character.
  2. I created a temporary string tmp_msg.
  3. Every time a Stream is received, a second temporary String "readMessage" is created out of that Stream.
  4. "readMessage" is searched for end character (".").
  5. If end character is not detected, "readMessage" is concatinated to tmp_msg. So when end character is not received first and second and third time tmp_msg=readMessage1+readMessage2+readMessage3.
  6. When end character "." is detected, tmp_msg is concatinated with last readMessage and bytes "buffer" are constructed out of it.

  7. "buffer" then is sent to User Interface, and tmp_msg is reinitialized to ""(empty string). here is the entire code: (no modification is to be done with BluetoothChat activity).

    public void run() { 
    Log.i(TAG, "BEGIN mConnectedThread");
    byte[] buffer = new byte[1024];
    int bytes;
    // Keep listening to the InputStream while connected
    String tmp_msg =""; 
    while (true) {
        try {
            // Read from the InputStream
            bytes = mmInStream.read(buffer);
            String readMessage = new String(buffer, 0,bytes);
            if (readMessage.contains(".")){
                tmp_msg+=readMessage;
                byte[] buffer1 = tmp_msg.getBytes();
                int bytes1=buffer1.length;
                tmp_msg="";
                // Send the obtained bytes to the UI Activity
                mHandler.obtainMessage(BluetoothChat.MESSAGE_READ,bytes1,-1,buffer1).sendToTarget();
            }else{
                tmp_msg+=readMessage;
            }
        } catch (IOException e) {
        //  Log.e(TAG, "disconnected", e);
            connectionLost();
            // Start the service over to restart listening mode
            BluetoothChatService.this.start();
            break;
        }
    }
}

Upvotes: 1

Ricky Nguyen Anh Giau
Ricky Nguyen Anh Giau

Reputation: 87

My way: I build a textView in MainActivity with its id being txtReceive.

@Override
public void run() {
    byte[] buffer=new byte[1024];
    int bytes;
    while(true) {
        try {
            bytes = inputStream.read(buffer);
            final String strReceived = new String(buffer, 0, bytes);
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    txtReceive.append(strReceived);
                }
            });
        } catch (Exception e) {
            Log.d(TAG, "loi ");
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    txtReceive.setText("Error");
                }
            });
        }
    }
}

Upvotes: -1

add_em_
add_em_

Reputation: 1

I think there are many good answers. My contribution is to process each digit one at a time as it comes into the Bluetooth input stream as follows. The value of this is to ensure that every set of data is one value in length (as a String), which can be processed very easily by putting each new value (contained in the readMessage String in the main Activity Handler) into a List. That way, you can then use the List(String) (the editor won't let me use <>'s) object to process the data back into real numbers by extracting via

Integer.valueOf(List(String) object passed in here)

// Keep listening to the InputStream while connected while (true) {

         try {
             byte[] buffer = new byte[1]; // make this one byte to pass one digit at a time through Bluetooth Handler
             String readMessage;
             int bytes;
            if (mmInStream.available()>2) { 
                try {
                   // Read from the InputStream
                    bytes = mmInStream.read(buffer); 
                    readMessage = new String(buffer, 0, bytes);

                   }catch (IOException e) {
                    Log.e(TAG, "disconnected", e);
                    break;
                }
                 // Send the obtained bytes to the UI Activity
                 mHandler.obtainMessage(HomeBlueRemote.MESSAGE_READ, bytes, -1, readMessage)
                      .sendToTarget();
    }

Upvotes: 0

Lukeskymuh
Lukeskymuh

Reputation: 9

I found it!

You have to reset the buffer:

buffer = new byte [1024];

before this:

bytes = mmInStream.read(buffer);

At least it worked for me, and no sleep command is needed.

Upvotes: 0

Felipe Gualberto
Felipe Gualberto

Reputation: 2389

Try this:

public void run() {
        byte[] buffer;
        ArrayList<Integer> arr_byte = new ArrayList<Integer>();
        while (true) {
            try {
                int data = mmInStream.read();
                if(mmInStream.available()>0) {
                    arr_byte.add(data);
                } else {
                    arr_byte.add(data);
                    buffer = new byte[arr_byte.size()];
                    for(int i = 0 ; i < arr_byte.size() ; i++) {
                        buffer[i] = arr_byte.get(i).byteValue();
                    }
                    Log.e("INPUT",new String(buffer));
                    mHandler.obtainMessage(MESSAGE_READ, bytes, -1, buffer)
                            .sendToTarget();
                    arr_byte = new ArrayList<Integer>();
                }
            } catch (IOException e) {
                break;
            }
        }
    }

I had this problem too. Now is working good. Without � Characters.

Upvotes: -1

papucho
papucho

Reputation: 129

I have a this problem and I've solved the problem of this characters � in this way

public void run() {        
    int bytes; // bytes returned from read()
    int availableBytes = 0;        
    // Keep listening to the InputStream until an exception occurs
    while (needRun) {
        try {
            availableBytes = mmInStream.available();
            if(availableBytes > 0){
                byte[] buffer = new byte[availableBytes];  // buffer store for the stream
                // Read from the InputStream


                bytes = mmInStream.read(buffer);
                Log.d("mmInStream.read(buffer);", new String(buffer));
                if( bytes > 0 ){                        
                    // Send the obtained bytes to the UI activity
                    mHandler.obtainMessage(MESSAGE_READ, bytes, -1, buffer).sendToTarget();                     
                }                                   
            }
        } catch (IOException e) {
            Log.d("Error reading", e.getMessage());
            e.printStackTrace();
            break;
        }
    }
}

Upvotes: 3

Ryan Harris
Ryan Harris

Reputation: 31

Radu's fix works fantastic!. I myself have been working on this issue for quite some time now using the Bluetooth Chat sample code. Below is what i'm using to capture and display temperature reading from a remote sensor:

  // Keep listening to the InputStream while connected
        while (true) {

             try {
                 byte[] buffer = new byte[128];
                 String readMessage;
                 int bytes;
                if (mmInStream.available()>2) { 
                    try {
                       // Read from the InputStream
                        bytes = mmInStream.read(buffer); 
                        readMessage = new String(buffer, 0, bytes);

                       }catch (IOException e) {
                        Log.e(TAG, "disconnected", e);
                        break;
                    }
                     // Send the obtained bytes to the UI Activity
                     mHandler.obtainMessage(HomeBlueRemote.MESSAGE_READ, bytes, -1, readMessage)
                          .sendToTarget();
        }
        else {
            SystemClock.sleep(100);
               }
            } catch (IOException e) {

                e.printStackTrace();
            }

       }

    }

As u see, I modified the (buffer.available() > 0) to > 2. This is because the my micro-controller is sending 2 bytes for the temperature. . Prior to this fix, inputstream for the byte count would vary, sometimes only capturing 1 byte which messed up the temperature display reading in the Android app. Again, out all the suggestions on the web, Radu has the best workaround for the android inputstream bug.

Upvotes: 1

Radu
Radu

Reputation: 2074

Two things I noticed with your code:

  • First of all sending further down to your app a reference to the buffer in which you read is not always a good solution: What if in the meantime the buffer gets overridden? See this bug on stackoverflow for example You can bypass this by making a copy of the data (for example use buffer.clone()) which you have read from Bluetooth, or if you don't like using too much memory you can make your read buffer a circular one.

  • You should be able to recompile your data even if it is received in separate packets (but packets are received in a short time span). You can make start/stop flags for instance. Ofc it still depends on the type of object you send over Bluetooth...

And now a possible solution if the 2 previous warnings are of no use is this:

Instead of an infinite loop which calls .read - a blocking call - you can do something like this:

while(true) {
     if mmInStream.getAvailable()>0 { 
          -your read code here-
     }
     else SystemClock.sleep(100);
}

It's a hack and it might still sometimes read only some part of the message - but it will be very rare!

Pls vote up/correct if useful!

Upvotes: 15

Related Questions