Figure 1: The enabling Bluetooth dialog.
The Android platform includes support for the Bluetooth network stack, which allows a device to wirelessly exchange data with other Bluetooth devices. The application framework provides access to the Bluetooth functionality through the Android Bluetooth APIs. These APIs let applications wirelessly connect to other Bluetooth devices, enabling point-to-point and multipoint wireless features.
Using the Bluetooth APIs, an Android application can perform the following:
This document describes how to us the Android Bluetooth APIs to accomplish the four major tasks necessary to communicate using Bluetooth: setting up Bluetooth, finding devices that are either paired or available in the local area, connecting devices, and transferring data between devices.
All of the Bluetooth APIs are available in the {@link android.bluetooth} package. Here's a summary of the classes you will need to create Bluetooth connections:
In order to use Bluetooth features in your application, you need to declare at least one of two Bluetooth permissions: {@link android.Manifest.permission#BLUETOOTH} and {@link android.Manifest.permission#BLUETOOTH_ADMIN}.
You must request the {@link android.Manifest.permission#BLUETOOTH} permission in order to perform any Bluetooth communication, such as requesting a connection, accepting a connection, and transferring data.
You must request the {@link android.Manifest.permission#BLUETOOTH_ADMIN} permission in order to initiate device discovery or manipulate Bluetooth settings. Most applications need this permission solely for the ability to discover local Bluetooth devices. The other abilities granted by this permission should not be used, unless the application is a "power manager" that will modify Bluetooth settings upon user request. Note: If you use {@link android.Manifest.permission#BLUETOOTH_ADMIN} permission, then must also have the {@link android.Manifest.permission#BLUETOOTH} permission.
Declare the Bluetooth permission(s) in your application manifest file. For example:
<manifest ... > <uses-permission android:name="android.permission.BLUETOOTH" /> ... </manifest>
See the <uses-permission> reference for more information about declaring application permissions.
Figure 1: The enabling Bluetooth dialog.
Before your application can communicate over Bluetooth, you need to verify that Bluetooth is supported on the device, and if so, ensure that it is enabled.
If Bluetooth is not supported, then you should gracefully disable any Bluetooth features. If Bluetooth is supported, but disabled, then you can request that the user enable Bluetooth without leaving your application. This setup is accomplished in two steps, using the {@link android.bluetooth.BluetoothAdapter}.
The {@link android.bluetooth.BluetoothAdapter} is required for any and all Bluetooth activity. To get the {@link android.bluetooth.BluetoothAdapter}, call the static {@link android.bluetooth.BluetoothAdapter#getDefaultAdapter()} method. This returns a {@link android.bluetooth.BluetoothAdapter} that represents the device's own Bluetooth adapter (the Bluetooth radio). There's one Bluetooth adapter for the entire system, and your application can interact with it using this object. If {@link android.bluetooth.BluetoothAdapter#getDefaultAdapter()} returns null, then the device does not support Bluetooth and your story ends here. For example:
BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
if (mBluetoothAdapter == null) {
// Device does not support Bluetooth
}
Next, you need to ensure that Bluetooth is enabled. Call {@link android.bluetooth.BluetoothAdapter#isEnabled()} to check whether Bluetooth is currently enable. If this method returns false, then Bluetooth is disabled. To request that Bluetooth be enabled, call {@link android.app.Activity#startActivityForResult(Intent,int) startActivityForResult()} with the {@link android.bluetooth.BluetoothAdapter#ACTION_REQUEST_ENABLE} action Intent. This will issue a request to enable Bluetooth through the system settings (without stopping your application). For example:
if (!mBluetoothAdapter.isEnabled()) {
Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}
A dialog will appear requesting user permission to enable Bluetooth, as shown in Figure 1. If the user responds "Yes," the system will begin to enable Bluetooth and focus will return to your application once the process completes (or fails).
If enabling Bluetooth succeeds, your Activity will receive the {@link android.app.Activity#RESULT_OK} result code in the {@link android.app.Activity#onActivityResult(int,int,Intent) onActivityResult()} callback. If Bluetooth was not enabled due to an error (or the user responded "No") then the result code will be {@link android.app.Activity#RESULT_CANCELED}.
Optionally, your application can also listen for the {@link android.bluetooth.BluetoothAdapter#ACTION_STATE_CHANGED} broadcast Intent, which the system will broadcast whenever the Bluetooth state has changed. This broadcast contains the extra fields {@link android.bluetooth.BluetoothAdapter#EXTRA_STATE} and {@link android.bluetooth.BluetoothAdapter#EXTRA_PREVIOUS_STATE}, containing the new and old Bluetooth states, respectively. Possible values for these extra fields are {@link android.bluetooth.BluetoothAdapter#STATE_TURNING_ON}, {@link android.bluetooth.BluetoothAdapter#STATE_ON}, {@link android.bluetooth.BluetoothAdapter#STATE_TURNING_OFF}, and {@link android.bluetooth.BluetoothAdapter#STATE_OFF}. Listening for this broadcast can be useful to detect changes made to the Bluetooth state while your app is running.
Tip: Enabling discoverability will automatically enable Bluetooth. If you plan to consistently enable device discoverability before performing Bluetooth activity, you can skip step 2 above. Read about enabling discoverability, below.
Using the {@link android.bluetooth.BluetoothAdapter}, you can find remote Bluetooth devices either through device discovery or by querying the list of paired (bonded) devices.
Device discovery is a scanning procedure that searches the local area for Bluetooth enabled devices and then requesting some information about each one (this is sometimes referred to as "discovering," "inquiring" or "scanning"). However, a Bluetooth device within the local area will respond to a discovery request only if it is currently enabled to be discoverable. If a device is discoverable, it will respond to the discovery request by sharing some information, such as the device name, class, and its unique MAC address. Using this information, the device performing discovery can then choose to initiate a connection to the discovered device.
Once a connection is made with a remote device for the first time, a pairing request is automatically presented to the user. When a device is paired, the basic information about that device (such as the device name, class, and MAC address) is saved and can be read using the Bluetooth APIs. Using the known MAC address for a remote device, a connection can be initiated with it at any time without performing discovery (assuming the device is within range).
Remember there is a difference between being paired and being connected. To be paired means that two devices are aware of each other's existence, have a shared link-key that can be used for authentication, and are capable of establishing an encrypted connection with each other. To be connected means that the devices currently share an RFCOMM channel and are able to transmit data with each other. The current Android Bluetooth API's require devices to be paired before an RFCOMM connection can be established. (Pairing is automatically performed when you initiate an encrypted connection with the Bluetooth APIs.)
The following sections describe how to find devices that have been paired, or discover new devices using device discovery.
Note: Android-powered devices are not discoverable by default. A user can make the device discoverable for a limited time through the system settings, or an application can request that the user enable discoverability without leaving the application. How to enable discoverability is discussed below.
Before performing device discovery, its worth querying the set of paired devices to see if the desired device is already known. To do so, call {@link android.bluetooth.BluetoothAdapter#getBondedDevices()}. This will return a Set of {@link android.bluetooth.BluetoothDevice}s representing paired devices. For example, you can query all paired devices and then show the name of each device to the user, using an ArrayAdapter:
Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();
// If there are paired devices
if (pairedDevices.size() > 0) {
// Loop through paired devices
for (BluetoothDevice device : pairedDevices) {
// Add the name and address to an array adapter to show in a ListView
mArrayAdapter.add(device.getName() + "\n" + device.getAddress());
}
}
All that's needed from the {@link android.bluetooth.BluetoothDevice} object in order to initiate a connection is the MAC address. In this example, it's saved as a part of an ArrayAdapter that's shown to the user. The MAC address can later be extracted in order to initiate the connection. You can learn more about creating a connection in the section about Connecting Devices.
To start discovering devices, simply call {@link android.bluetooth.BluetoothAdapter#startDiscovery()}. The process is asynchronous and the method will immediately return with a boolean indicating whether discovery has successfully started. The discovery process usually involves an inquiry scan of about 12 seconds, followed by a page scan of each found device to retrieve its Bluetooth name.
Your application must register a BroadcastReceiver for the {@link android.bluetooth.BluetoothDevice#ACTION_FOUND} Intent in order to receive information about each device discovered. For each device, the system will broadcast the {@link android.bluetooth.BluetoothDevice#ACTION_FOUND} Intent. This Intent carries the extra fields {@link android.bluetooth.BluetoothDevice#EXTRA_DEVICE} and {@link android.bluetooth.BluetoothDevice#EXTRA_CLASS}, containing a {@link android.bluetooth.BluetoothDevice} and a {@link android.bluetooth.BluetoothClass}, respectively. For example, here's how you can register to handle the broadcast when devices are discovered:
// Create a BroadcastReceiver for ACTION_FOUND
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
// When discovery finds a device
if (BluetoothDevice.ACTION_FOUND.equals(action)) {
// Get the BluetoothDevice object from the Intent
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
// Add the name and address to an array adapter to show in a ListView
mArrayAdapter.add(device.getName() + "\n" + device.getAddress());
}
}
};
// Register the BroadcastReceiver
IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
registerReceiver(mReceiver, filter); // Don't forget to unregister during onDestroy
All that's needed from the {@link android.bluetooth.BluetoothDevice} object in order to initiate a connection is the MAC address. In this example, it's saved as a part of an ArrayAdapter that's shown to the user. The MAC address can later be extracted in order to initiate the connection. You can learn more about creating a connection in the section about Connecting Devices.
Caution: Performing device discovery is a heavy procedure for the Bluetooth adapter and will consume a lot of its resources. Once you have found a device to connect, be certain that you always stop discovery with {@link android.bluetooth.BluetoothAdapter#cancelDiscovery()} before attempting a connection. Also, if you already hold a connection with a device, then performing discovery can significantly reduce the bandwidth available for the connection, so you should not perform discovery while connected.
If you would like to make the local device discoverable to other devices, call {@link android.app.Activity#startActivityForResult(Intent,int)} with the {@link android.bluetooth.BluetoothAdapter#ACTION_REQUEST_DISCOVERABLE} action Intent. This will issue a request to enable discoverable mode through the system settings (without stopping your application). By default, the device will become discoverable for 120 seconds. You can define a different duration by adding the {@link android.bluetooth.BluetoothAdapter#EXTRA_DISCOVERABLE_DURATION} Intent extra (maximum duration is 300 seconds). For example:
Intent discoverableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE); discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300); startActivity(discoverableIntent);
Figure 2: The enabling discoverability dialog.
A dialog will be displayed, requesting user permission to make the device discoverable, as shown in Figure 2. If the user responds "Yes," then the device will become discoverable for the specified amount of time. Your Activity will then receive a call to the {@link android.app.Activity#onActivityResult(int,int,Intent) onActivityResult())} callback, with the result code equal to the duration that the device is discoverable. If the user responded "No" or if an error occurred, the result code will be Activity.RESULT_CANCELLED.
Note: If Bluetooth has not been enabled on the device, then enabling device discoverability will automatically enable Bluetooth.
The device will silently remain in discoverable mode for the allotted time. If you would like to be notified when the discoverable mode has changed, you can register a BroadcastReceiver for the {@link android.bluetooth.BluetoothAdapter#ACTION_SCAN_MODE_CHANGED} Intent. This will contain the extra fields {@link android.bluetooth.BluetoothAdapter#EXTRA_SCAN_MODE} and {@link android.bluetooth.BluetoothAdapter#EXTRA_PREVIOUS_SCAN_MODE}, which tell you the new and old scan mode, respectively. Possible values for each are {@link android.bluetooth.BluetoothAdapter#SCAN_MODE_CONNECTABLE_DISCOVERABLE}, {@link android.bluetooth.BluetoothAdapter#SCAN_MODE_CONNECTABLE}, or {@link android.bluetooth.BluetoothAdapter#SCAN_MODE_NONE}, which indicate that the device is either in discoverable mode, not in discoverable mode but still able to receive connections, or not in discoverable mode and unable to receive connections, respectively.
You do not need to enable device discoverability if you will be initiating the connection to a remote device. Enabling discoverability is only necessary when you want your application to host a server socket that will accept incoming connections, because the remote devices must be able to discover the device before it can initiate the connection.
In order to create a connection between your application on two devices, you must implement both the server-side and client-side mechanisms, because one device must open a server socket and the other one must initiate the connection (using the server device's MAC address to initiate a connection). The server and client are considered connected to each other when they each have a connected {@link android.bluetooth.BluetoothSocket} on the same RFCOMM channel. At this point, each device can obtain input and output streams and data transfer can begin, which is discussed in the section about Managing a Connection. This section describes how to initiate the connection between two devices.
The server device and the client device each obtain the required {@link android.bluetooth.BluetoothSocket} in different ways. The server will receive it when an incoming connection is accepted. The client will receive it when it opens an RFCOMM channel to the server.
Figure 3: The Bluetooth pairing dialog.
One implementation technique is to automatically prepare each device as a server, so that each one has a server socket open and listening for connections. Then either device can initiate a connection with the other and become the client. Alternatively, one device can explicitly "host" the connection and open a server socket on demand and the other device can simply initiate the connection.
Note: If the two devices have not been previously paired, then the Android framework will automatically show a pairing request notification or dialog to the user during the connection procedure, as shown in Figure 3. So when attempting to connect devices, your application does not need to be concerned about whether or not the devices are paired. Your RFCOMM connection attempt will block until the user has successfully paired, or will fail if the user rejects pairing, or if pairing fails or times out.
When you want to connect two devices, one must act as a server by holding an open {@link android.bluetooth.BluetoothServerSocket}. The purpose of the server socket is to listen for incoming connection requests and when one is accepted, provide a connected {@link android.bluetooth.BluetoothSocket}. When the {@link android.bluetooth.BluetoothSocket} is acquired from the {@link android.bluetooth.BluetoothServerSocket}, the {@link android.bluetooth.BluetoothServerSocket} can (and should) be discarded, unless you want to accept more connections.
A Universally Unique Identifier (UUID) is a standardized 128-bit format for a string ID used to uniquely identify information. The point of a UUID is that it's big enough that you can select any random and it won't clash. In this case, it's used to uniquely identify your application's Bluetooth service. To get a UUID to use with your application, you can use one of the many random UUID generators on the web, then initialize a {@link java.util.UUID} with {@link java.util.UUID#fromString(String)}.
Here's the basic procedure to set up a server socket and accept a connection:
The string is an identifiable name of your service, which the system will automatically write to a new Service Discovery Protocol (SDP) database entry on the device (the name is arbitrary and can simply be your application name). The UUID is also included in the SDP entry and will be the basis for the connection agreement with the client device. That is, when the client attempts to connect with this device, it will carry a UUID that uniquely identifies the service with which it wants to connect. These UUIDs must match in order for the connection to be accepted (in the next step).
This is a blocking call. It will return when either a connection has been accepted or an exception has occurred. A connection is accepted only when a remote device has sent a connection request with a UUID matching the one registered with this listening server socket. When successful, {@link android.bluetooth.BluetoothServerSocket#accept()} will return a connected {@link android.bluetooth.BluetoothSocket}.
This releases the server socket and all its resources, but does not close the connected {@link android.bluetooth.BluetoothSocket} that's been returned by {@link android.bluetooth.BluetoothServerSocket#accept()}. Unlike TCP/IP, RFCOMM only allows one connected client per channel at a time, so in most cases it makes sense to call {@link android.bluetooth.BluetoothServerSocket#close()} on the {@link android.bluetooth.BluetoothServerSocket} immediately after accepting a connected socket.
The {@link android.bluetooth.BluetoothServerSocket#accept()} call should not be executed in the main Activity UI thread because it is a blocking call and will prevent any other interaction with the application. It usually makes sense to do all work with a {@link android.bluetooth.BluetoothServerSocket} or {@link android.bluetooth.BluetoothSocket} in a new thread managed by your application. To abort a blocked call such as {@link android.bluetooth.BluetoothServerSocket#accept()}, call {@link android.bluetooth.BluetoothServerSocket#close()} on the {@link android.bluetooth.BluetoothServerSocket} (or {@link android.bluetooth.BluetoothSocket}) from another thread and the blocked call will immediately return. Note that all methods on a {@link android.bluetooth.BluetoothServerSocket} or {@link android.bluetooth.BluetoothSocket} are thread-safe.
Here's a simplified thread for the server component that accepts incoming connections:
private class AcceptThread extends Thread {
private final BluetoothServerSocket mmServerSocket;
public AcceptThread() {
// Use a temporary object that is later assigned to mmServerSocket,
// because mmServerSocket is final
BluetoothServerSocket tmp = null;
try {
// MY_UUID is the app's UUID string, also used by the client code
tmp = mAdapter.listenUsingRfcommWithServiceRecord(NAME, MY_UUID);
} catch (IOException e) { }
mmServerSocket = tmp;
}
public void run() {
BluetoothSocket socket = null;
// Keep listening until exception occurs or a socket is returned
while (true) {
try {
socket = mmServerSocket.accept();
} catch (IOException e) {
break;
}
// If a connection was accepted
if (socket != null) {
// Do work to manage the connection (in a separate thread)
manageConnectedSocket(socket);
mmServerSocket.close();
break;
}
}
}
/** Will cancel the listening socket, and cause the thread to finish */
public void cancel() {
try {
mmServerSocket.close();
} catch (IOException e) { }
}
}
In this example, only one incoming connection is desired, so as soon as a connection is accepted and the {@link android.bluetooth.BluetoothSocket} is acquired, the application sends the acquired {@link android.bluetooth.BluetoothSocket} to a separate thread, closes the {@link android.bluetooth.BluetoothServerSocket} and breaks the loop.
Note that when {@link android.bluetooth.BluetoothServerSocket#accept()} returns the {@link android.bluetooth.BluetoothSocket}, the socket is already connected, so you should not call {@link android.bluetooth.BluetoothSocket#connect()} (as you do from the client-side).
manageConnectedSocket() is a fictional method in the application
that will
initiate the thread for transferring data, which is discussed in the section
about Managing a Connection.
You should usually close your {@link android.bluetooth.BluetoothServerSocket} as soon as you are done listening for incoming connections. In this example, {@link android.bluetooth.BluetoothServerSocket#close()} is called as soon as the {@link android.bluetooth.BluetoothSocket} is acquired. You may also want to provide a public method in your thread that can close the private {@link android.bluetooth.BluetoothSocket} in the event that you need to stop listening on the server socket.
In order to initiate a connection with a remote device (a device holding an open server socket), you must first obtain a {@link android.bluetooth.BluetoothDevice} object that represents the remote device. (Getting a {@link android.bluetooth.BluetoothDevice} is covered in the above section about Finding Devices.) You must then use the {@link android.bluetooth.BluetoothDevice} to acquire a {@link android.bluetooth.BluetoothSocket} and initiate the connection.
Here's the basic procedure:
This initializes a {@link android.bluetooth.BluetoothSocket} that will connect to the {@link android.bluetooth.BluetoothDevice}. The UUID passed here must match the UUID used by the server device when it opened its {@link android.bluetooth.BluetoothServerSocket} (with {@link android.bluetooth.BluetoothAdapter#listenUsingRfcommWithServiceRecord(String, UUID)}). Using the same UUID is simply a matter of hard-coding the UUID string into your application and then referencing it from both the server and client code.
Upon this call, the system will perform an SDP lookup on the remote device in order to match the UUID. If the lookup is successful and the remote device accepts the connection, it will share the RFCOMM channel to use during the connection and {@link android.bluetooth.BluetoothSocket#connect()} will return. This method is a blocking call. If, for any reason, the connection fails or the {@link android.bluetooth.BluetoothSocket#connect()} method times out (after about 12 seconds), then it will throw an exception.
Because {@link android.bluetooth.BluetoothSocket#connect()} is a blocking call, this connection procedure should always be performed in a thread separate from the main Activity thread.
Note: You should always ensure that the device is not performing device discovery when you call {@link android.bluetooth.BluetoothSocket#connect()}. If discovery is in progress, then the connection attempt will be significantly slowed and is more likely to fail.
Here is a basic example of a thread that initiates a Bluetooth connection:
private class ConnectThread extends Thread {
private final BluetoothSocket mmSocket;
private final BluetoothDevice mmDevice;
public ConnectThread(BluetoothDevice device) {
// Use a temporary object that is later assigned to mmSocket,
// because mmSocket is final
BluetoothSocket tmp = null;
mmDevice = device;
// Get a BluetoothSocket to connect with the given BluetoothDevice
try {
// MY_UUID is the app's UUID string, also used by the server code
tmp = device.createRfcommSocketToServiceRecord(MY_UUID);
} catch (IOException e) { }
mmSocket = tmp;
}
public void run() {
// Cancel discovery because it will slow down the connection
mAdapter.cancelDiscovery();
try {
// Connect the device through the socket. This will block
// until it succeeds or throws an exception
mmSocket.connect();
} catch (IOException connectException) {
// Unable to connect; close the socket and get out
try {
mmSocket.close();
} catch (IOException closeException) { }
return;
}
// Do work to manage the connection (in a separate thread)
manageConnectedSocket(mmSocket);
}
/** Will cancel an in-progress connection, and close the socket */
public void cancel() {
try {
mmSocket.close();
} catch (IOException e) { }
}
}
Notice that {@link android.bluetooth.BluetoothAdapter#cancelDiscovery()} is called before the connection is made. You should always do this before connecting and it is safe to call without actually checking whether it is running or not (but if you do want to check, call {@link android.bluetooth.BluetoothAdapter#isDiscovering()}).
manageConnectedSocket() is a fictional method in the application
that will initiate the thread for transferring data, which is discussed in the section
about Managing a Connection.
When you're done with your {@link android.bluetooth.BluetoothSocket}, always call {@link android.bluetooth.BluetoothSocket#close()} to clean up. Doing so will immediately close the connected socket and clean up all internal resources.
When you have successfully connected two (or more) devices, each one will have a connected {@link android.bluetooth.BluetoothSocket}. This is where the fun begins because you can share data between devices. Using the {@link android.bluetooth.BluetoothSocket}, the general procedure to transfer arbitrary data is simple:
That's it.
There are, of course, implementation details to consider. First and foremost, you should use a dedicated thread for all stream reading and writing. This is important because both {@link java.io.InputStream#read(byte[])} and {@link java.io.OutputStream#write(byte[])} methods are blocking calls. {@link java.io.InputStream#read(byte[])} will block until there is something to read from the stream. {@link java.io.OutputStream#write(byte[])} does not usually block, but can block for flow control if the remote device is not calling {@link java.io.InputStream#read(byte[])} quickly enough and the intermediate buffers are full. So, your main loop in the thread should be dedicated to reading from the {@link java.io.InputStream}. A separate public method in the thread can be used to initiate writes to the {@link java.io.OutputStream}.
Here's an example of how this might look:
private class ConnectedThread extends Thread {
private final BluetoothSocket mmSocket;
private final InputStream mmInStream;
private final OutputStream mmOutStream;
public ConnectedThread(BluetoothSocket socket) {
mmSocket = socket;
InputStream tmpIn = null;
OutputStream tmpOut = null;
// Get the input and output streams, using temp objects because
// member streams are final
try {
tmpIn = socket.getInputStream();
tmpOut = socket.getOutputStream();
} catch (IOException e) { }
mmInStream = tmpIn;
mmOutStream = tmpOut;
}
public void run() {
byte[] buffer = new byte[1024]; // buffer store for the stream
int bytes; // bytes returned from read()
// Keep listening to the InputStream until an exception occurs
while (true) {
try {
// Read from the InputStream
bytes = mmInStream.read(buffer);
// Send the obtained bytes to the UI Activity
mHandler.obtainMessage(MESSAGE_READ, bytes, -1, buffer)
.sendToTarget();
} catch (IOException e) {
break;
}
}
}
/* Call this from the main Activity to send data to the remote device */
public void write(byte[] bytes) {
try {
mmOutStream.write(bytes);
} catch (IOException e) { }
}
/* Call this from the main Activity to shutdown the connection */
public void cancel() {
try {
mmSocket.close();
} catch (IOException e) { }
}
}
The constructor acquires the necessary streams and once executed, the thread will wait for data to come through the InputStream. When {@link java.io.InputStream#read(byte[])} returns with bytes from the stream, the data is sent to the main Activity using a member Handler from the parent class. Then it goes back and waits for more bytes from the stream.
Sending outgoing data is as simple as calling the thread's
write() method from the main Activity and passing in the bytes to
be sent. This method then simply calls {@link
java.io.OutputStream#write(byte[])} to send the data to the remote device.
The thread's cancel() method is important so that the connection
can be
terminated at any time by closing the {@link android.bluetooth.BluetoothSocket}.
This should always be called when you're done using the Bluetooth
connection.
For a complete demonstration using the Bluetooth APIs, see the Bluetooth Chat sample app.