Android BluetoothSocket.isConnected always returns false

Question

I am trying to detect whether a bluetooth device is currently connected to an Android device using API 14 or better. It seems like I should be able to use the BluetoothSocket.isConnected() method, but no matter what I've done, so far I just get false back for anything, connected or not.

AndroidManifest includes these lines:

<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />

<!-- Locale 4.x supports API 14 or greater. -->
<uses-sdk android:minSdkVersion="14" android:targetSdkVersion="17" />

<uses-feature android:name="android.hardware.bluetooth" />

And the code in question:

protected void onCreate(final Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();

    for (BluetoothDevice device : pairedDevices) {
        Log.i(Constants.LOG_TAG, String.format(Locale.US, "Device: %s connected: %b", device.getName(), isConnected(device))); //$NON-NLS-1$z
    }
}

private boolean isConnected(BluetoothDevice device) {
    BluetoothSocket socket = null;

    // Get a BluetoothSocket for a connection with the given BluetoothDevice
    UUID SPP_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
    try {
        socket = device.createRfcommSocketToServiceRecord(SPP_UUID);
    } catch (IOException e) {
        Log.e(Constants.LOG_TAG, e.getMessage()); //$NON-NLS-1$z
        return false;
    }

    Log.i(Constants.LOG_TAG, socket.toString()); //$NON-NLS-1$z

    return socket.isConnected();
}

No errors are thrown, it simply returns "false" 100% of the time. Is there something that I'm not doing right?

score 3 · Answer 1 · answered Jul 06 '14 at 10:19

I believe that jkane001 already solved his problem, so I hope this answer will help someone else.

First of all after socket creation

socket = device.createRfcommSocketToServiceRecord(SPP_UUID);

you shall init connection by

socket.connect();

After that you'll be able to check connection state using socket.isConnected()

Since connect() method is not blocking, so immediately after socket may be not connected yet. I suggest to use something like this

while(!socket.isConnected() && trial++ < 3){
    try {
        Thread.sleep(300);
    } catch (Exception e) {}
}

By the way, I found that on some android devices isConnected() always returns false. In such case just try to write something to socket and check if there is no exception.

I have found that after a connection is lost due to poor signal, if isConnected() is called, it still returns True. So I have resorted to sending something to the socket and catching the exception. — VectorVictor, Feb 10 '17 at 18:10
@VectorVictor correct. isConnected() isn't a reliable method to check if the connection alive. — Alex, Feb 13 '17 at 09:30

score 3 · Answer 2 · answered Feb 06 '15 at 18:51

Apparently there are devices and/or Android versions where isConnected() is implemented (i.e. the function exists and you can call it), but worse than useless because it always returns false. I have an Alcatel phone in on my desk running Android 4.2.2 which exhibits this behavior.

My code was assuming it was disconnected, and so killed my connection thread and this was driving me crazy for a long time. However, I removed the isConnected() call and assumed it was connected, and everything works fine! I haven't found a better way to check for a valid connection other than waiting for an error and declaring the connection dead. The blocked read() in the thread eventually does fail.

We have reports from the field that sound similar, and 2 of the 2 problem devices for which we know the version are also on 4.2.2. Haven't yet deployed the fix, so not sure if it fixed those cases yet.

score 0 · Answer 3 · answered Feb 09 '13 at 22:06

0

First off, why are you using reflection?! That's a red flag to me. The APIs allow you to talk to another device via bluetooth, see this link so you should not use reflection.

A socket will always return not connected before its connect method is called. It seems that your code obtains the socket but never tries to make a connection with it. You first need to call this method.

answered Feb 09 '13 at 22:06

Ameen

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The reflection part came from the accepted answer to this question: http://stackoverflow.com/questions/3397071/service-discovery-failed-exception-using-bluetooth-on-android. I wasn't thrilled with the idea of reflection, but I think I remember reading somewhere else that you should not rely on the UUID from the original question. Having said that, the important issue for me is the second part of your answer - I'm trying to find any BT devices that are connected, not trying to connect any myself. Is that not possible? I'm trying to avoid having to create a service to monitor BT state changes. – jkane001 Feb 10 '13 at 00:05
Ameen was right, after a more careful read of the SO answers and the Android docs, I realized that reflection was not necessary here. I've updated my original question with a better "isConnected" method, but my question remains: is there a way to detect if a BT device is connected without being the one to connect it? – jkane001 Feb 10 '13 at 00:17

Android BluetoothSocket.isConnected always returns false

3 Answers3