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Android.com

# Bluetooth

## Quickview

- Android's bluetooth APIs allow your application to perform wireless data transactions with other devices

## In this document

1. The Basics
2. Bluetooth Permissions
3. Setting Up Bluetooth
4. Finding Devices
   1. Querying paired devices
   2. Discovering devices
5. Connecting Devices
   1. Connecting as a server
   2. Connecting as a client
6. Managing a Connection
7. Working with Profiles
   1. Vendor-specific AT commands

## Key classes

1. `BluetoothAdapter`
2. `BluetoothDevice`
3. `BluetoothSocket`
4. `BluetoothServerSocket`

## Related samples

1. Bluetooth Chat

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:

- Scan for other Bluetooth devices
- Query the local Bluetooth adapter for paired Bluetooth devices
- Establish RFCOMM channels
- Connect to other devices through service discovery
- Transfer data to and from other devices
- Manage multiple connections

## The Basics

This document describes how to use 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 `android.bluetooth` package. Here's a summary of the classes and interfaces you will need to create Bluetooth connections:

`BluetoothAdapter`
  Represents the local Bluetooth adapter (Bluetooth radio). The `BluetoothAdapter` is the entry-point for all Bluetooth interaction. Using this, you can discover other Bluetooth devices, query a list of bonded (paired) devices, instantiate a `BluetoothDevice` using a known MAC address, and create a `BluetoothServerSocket` to listen for communications from other devices.
`BluetoothDevice`
  Represents a remote Bluetooth device. Use this to request a connection with a remote device through a `BluetoothSocket` or query information about the device such as its name, address, class, and bonding state.
`BluetoothSocket`
  Represents the interface for a Bluetooth socket (similar to a TCP `Socket`). This is the connection point that allows an application to exchange data with another Bluetooth device via InputStream and OutputStream.
`BluetoothServerSocket`
  Represents an open server socket that listens for incoming requests (similar to a TCP `ServerSocket`). In order to connect two Android devices, one device must open a server socket with this class. When a remote Bluetooth device makes a connection request to the this device, the `BluetoothServerSocket` will return a connected `BluetoothSocket` when the connection is accepted.
`BluetoothClass`
  Describes the general characteristics and capabilities of a Bluetooth device. This is a read-only set of properties that define the device's major and minor device classes and its services. However, this does not reliably describe all Bluetooth profiles and services supported by the device, but is useful as a hint to the device type.
`BluetoothProfile`
  An interface that represents a Bluetooth profile. A Bluetooth profile is a wireless interface specification for Bluetooth-based communication between devices. An example is the Hands-Free profile. For more discussion of profiles, see Working with Profiles
`BluetoothHeadset`
  Provides support for Bluetooth headsets to be used with mobile phones. This includes both Bluetooth Headset and Hands-Free (v1.5) profiles.
`BluetoothA2dp`
  Defines how high quality audio can be streamed from one device to another over a Bluetooth connection. "A2DP" stands for Advanced Audio Distribution Profile.
`BluetoothProfile.ServiceListener`
  An interface that notifies `BluetoothProfile` IPC clients when they have been connected to or disconnected from the service (that is, the internal service that runs a particular profile).

## Bluetooth Permissions

In order to use Bluetooth features in your application, you need to declare at least one of two Bluetooth permissions: `BLUETOOTH` and `BLUETOOTH_ADMIN`.

You must request the `BLUETOOTH` permission in order to perform any Bluetooth communication, such as requesting a connection, accepting a connection, and transferring data.

You must request the `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 `BLUETOOTH_ADMIN` permission, then must also have the `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.

## Setting Up Bluetooth

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 `BluetoothAdapter`.

1. Get the `BluetoothAdapter`

   The `BluetoothAdapter` is required for any and all Bluetooth activity. To get the `BluetoothAdapter`, call the static `getDefaultAdapter()` method. This returns a `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 `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
       }

2. Enable Bluetooth

   Next, you need to ensure that Bluetooth is enabled. Call `isEnabled()` to check whether Bluetooth is currently enable. If this method returns false, then Bluetooth is disabled. To request that Bluetooth be enabled, call `startActivityForResult()` with the `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 `RESULT_OK` result code in the `onActivityResult()` callback. If Bluetooth was not enabled due to an error (or the user responded "No") then the result code will be `RESULT_CANCELED`.

Optionally, your application can also listen for the `ACTION_STATE_CHANGED` broadcast Intent, which the system will broadcast whenever the Bluetooth state has changed. This broadcast contains the extra fields `EXTRA_STATE` and `EXTRA_PREVIOUS_STATE`, containing the new and old Bluetooth states, respectively. Possible values for these extra fields are `STATE_TURNING_ON`, `STATE_ON`, `STATE_TURNING_OFF`, and `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.

## Finding Devices

Using the `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.

### Querying paired devices

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 `getBondedDevices()`. This will return a Set of `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 `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.

### Discovering devices

To start discovering devices, simply call `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 `ACTION_FOUND` Intent in order to receive information about each device discovered. For each device, the system will broadcast the `ACTION_FOUND` Intent. This Intent carries the extra fields `EXTRA_DEVICE` and `EXTRA_CLASS`, containing a `BluetoothDevice` and a `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 `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 `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.

#### Enabling discoverability

If you would like to make the local device discoverable to other devices, call `startActivityForResult(Intent, int)` with the `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 `EXTRA_DISCOVERABLE_DURATION` Intent extra. The maximum duration an app can set is 3600 seconds, and a value of 0 means the device is always discoverable. Any value below 0 or above 3600 is automatically set to 120 secs). For example, this snippet sets the duration to 300:

    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 `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 `ACTION_SCAN_MODE_CHANGED` Intent. This will contain the extra fields `EXTRA_SCAN_MODE` and `EXTRA_PREVIOUS_SCAN_MODE`, which tell you the new and old scan mode, respectively. Possible values for each are `SCAN_MODE_CONNECTABLE_DISCOVERABLE`, `SCAN_MODE_CONNECTABLE`, or `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.

## Connecting Devices

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 `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 `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.

### Connecting as a server

When you want to connect two devices, one must act as a server by holding an open `BluetoothServerSocket`. The purpose of the server socket is to listen for incoming connection requests and when one is accepted, provide a connected `BluetoothSocket`. When the `BluetoothSocket` is acquired from the `BluetoothServerSocket`, the `BluetoothServerSocket` can (and should) be discarded, unless you want to accept more connections.

## About UUID

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 `UUID` with `fromString(String)`.

Here's the basic procedure to set up a server socket and accept a connection:

1. Get a `BluetoothServerSocket` by calling the `listenUsingRfcommWithServiceRecord(String, UUID)`.

   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).

2. Start listening for connection requests by calling `accept()`.

   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, `accept()` will return a connected `BluetoothSocket`.

3. Unless you want to accept additional connections, call `close()`.

   This releases the server socket and all its resources, but does not close the connected `BluetoothSocket` that's been returned by `accept()`. Unlike TCP/IP, RFCOMM only allows one connected client per channel at a time, so in most cases it makes sense to call `close()` on the `BluetoothServerSocket` immediately after accepting a connected socket.

The `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 `BluetoothServerSocket` or `BluetoothSocket` in a new thread managed by your application. To abort a blocked call such as `accept()`, call `close()` on the `BluetoothServerSocket` (or `BluetoothSocket`) from another thread and the blocked call will immediately return. Note that all methods on a `BluetoothServerSocket` or `BluetoothSocket` are thread-safe.

#### Example

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 = mBluetoothAdapter.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 `BluetoothSocket` is acquired, the application sends the acquired `BluetoothSocket` to a separate thread, closes the `BluetoothServerSocket` and breaks the loop.

Note that when `accept()` returns the `BluetoothSocket`, the socket is already connected, so you should not call `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 `BluetoothServerSocket` as soon as you are done listening for incoming connections. In this example, `close()` is called as soon as the `BluetoothSocket` is acquired. You may also want to provide a public method in your thread that can close the private `BluetoothSocket` in the event that you need to stop listening on the server socket.

### Connecting as a client

In order to initiate a connection with a remote device (a device holding an open server socket), you must first obtain a `BluetoothDevice` object that represents the remote device. (Getting a `BluetoothDevice` is covered in the above section about Finding Devices.) You must then use the `BluetoothDevice` to acquire a `BluetoothSocket` and initiate the connection.

Here's the basic procedure:

1. Using the `BluetoothDevice`, get a `BluetoothSocket` by calling `createRfcommSocketToServiceRecord(UUID)`.

   This initializes a `BluetoothSocket` that will connect to the `BluetoothDevice`. The UUID passed here must match the UUID used by the server device when it opened its `BluetoothServerSocket` (with `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.

2. Initiate the connection by calling `connect()`.

   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 `connect()` will return. This method is a blocking call. If, for any reason, the connection fails or the `connect()` method times out (after about 12 seconds), then it will throw an exception.

   Because `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 `connect()`. If discovery is in progress, then the connection attempt will be significantly slowed and is more likely to fail.

#### Example

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
            mBluetoothAdapter.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 `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 `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 `BluetoothSocket`, always call `close()` to clean up. Doing so will immediately close the connected socket and clean up all internal resources.

## Managing a Connection

When you have successfully connected two (or more) devices, each one will have a connected `BluetoothSocket`. This is where the fun begins because you can share data between devices. Using the `BluetoothSocket`, the general procedure to transfer arbitrary data is simple:

1. Get the `InputStream` and `OutputStream` that handle transmissions through the socket, via `getInputStream()` and `getOutputStream()`, respectively.
2. Read and write data to the streams with `read(byte[])` and `write(byte[])`.

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 `read(byte[])` and `write(byte[])` methods are blocking calls. `read(byte[])` will block until there is something to read from the stream. `write(byte[])` does not usually block, but can block for flow control if the remote device is not calling `read(byte[])` quickly enough and the intermediate buffers are full. So, your main loop in the thread should be dedicated to reading from the `InputStream`. A separate public method in the thread can be used to initiate writes to the `OutputStream`.

#### Example

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 `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 `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 `BluetoothSocket`. This should always be called when you're done using the Bluetooth connection.

For a demonstration of using the Bluetooth APIs, see the Bluetooth Chat sample app.

## Working with Profiles

Starting in Android 3.0, the Bluetooth API includes support for working with Bluetooth profiles. A Bluetooth profile is a wireless interface specification for Bluetooth-based communication between devices. An example is the Hands-Free profile. For a mobile phone to connect to a wireless headset, both devices must support the Hands-Free profile.

You can implement the interface `BluetoothProfile` to write your own classes to support a particular Bluetooth profile. The Android Bluetooth API provides implementations for the following Bluetooth profiles:

- Headset. The Headset profile provides support for Bluetooth headsets to be used with mobile phones. Android provides the `BluetoothHeadset` class, which is a proxy for controlling the Bluetooth Headset Service via interprocess communication (IPC). This includes both Bluetooth Headset and Hands-Free (v1.5) profiles. The `BluetoothHeadset` class includes support for AT commands. For more discussion of this topic, see Vendor-specific AT commands
- A2DP. The Advanced Audio Distribution Profile (A2DP) profile defines how high quality audio can be streamed from one device to another over a Bluetooth connection. Android provides the `BluetoothA2dp` class, which is a proxy for controlling the Bluetooth A2DP Service via IPC.

Here are the basic steps for working with a profile:

1. Get the default adapter, as described in Setting Up Bluetooth.
2. Use `getProfileProxy()` to establish a connection to the profile proxy object associated with the profile. In the example below, the profile proxy object is an instance of `BluetoothHeadset`.
3. Set up a `BluetoothProfile.ServiceListener`. This listener notifies `BluetoothProfile` IPC clients when they have been connected to or disconnected from the service.
4. In `onServiceConnected()`, get a handle to the profile proxy object.
5. Once you have the profile proxy object, you can use it to monitor the state of the connection and perform other operations that are relevant to that profile.

For example, this code snippet shows how to connect to a `BluetoothHeadset` proxy object so that you can control the Headset profile:

    BluetoothHeadset mBluetoothHeadset;

    // Get the default adapter
    BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();

    // Establish connection to the proxy.
    mBluetoothAdapter.getProfileProxy(context, mProfileListener, BluetoothProfile.HEADSET);

    private BluetoothProfile.ServiceListener mProfileListener = new BluetoothProfile.ServiceListener() {
        public void onServiceConnected(int profile, BluetoothProfile proxy) {
            if (profile == BluetoothProfile.HEADSET) {
                mBluetoothHeadset = (BluetoothHeadset) proxy;
            }
        }
        public void onServiceDisconnected(int profile) {
            if (profile == BluetoothProfile.HEADSET) {
                mBluetoothHeadset = null;
            }
        }
    };

    // ... call functions on mBluetoothHeadset

    // Close proxy connection after use.
    mBluetoothAdapter.closeProfileProxy(mBluetoothHeadset);

### Vendor-specific AT commands

Starting in Android 3.0, applications can register to receive system broadcasts of pre-defined vendor-specific AT commands sent by headsets (such as a Plantronics +XEVENT command). For example, an application could receive broadcasts that indicate a connected device's battery level and could notify the user or take other action as needed. Create a broadcast receiver for the `ACTION_VENDOR_SPECIFIC_HEADSET_EVENT` intent to handle vendor-specific AT commands for the headset.

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