以谷歌自带的Bluetooth Chat举例说明，例子中有三个源文件，分别为：BluetoothChat.java, DeviceListActivity.java, BluetoothChatService.java。
其中BluetoothChat.java是主UI的Activity，DeviceListActivity.java是配对设备列表选择UI的Activity，BluetoothChatService.java是功能类内含多个
线程的定义。
1. 主UI中定义Handler成员变量mHandler：
// The Handler that gets information back from the BluetoothChatService private final Handler mHandler = new Handler() { @Override public void handleMessage(Message msg) { switch (msg.what) { case MESSAGE_STATE_CHANGE: if(D) Log.i(TAG, "MESSAGE_STATE_CHANGE: " + msg.arg1); switch (msg.arg1) { case BluetoothChatService.STATE_CONNECTED: setStatus(getString(R.string.title_connected_to, mConnectedDeviceName)); mConversationArrayAdapter.clear(); break; case BluetoothChatService.STATE_CONNECTING: setStatus(R.string.title_connecting); break; case BluetoothChatService.STATE_LISTEN: case BluetoothChatService.STATE_NONE: setStatus(R.string.title_not_connected); break; } break; case MESSAGE_WRITE: byte[] writeBuf = (byte[]) msg.obj; // construct a string from the buffer String writeMessage = new String(writeBuf); mConversationArrayAdapter.add("Me: " + writeMessage); break; case MESSAGE_READ: byte[] readBuf = (byte[]) msg.obj; // construct a string from the valid bytes in the buffer String readMessage = new String(readBuf, 0, msg.arg1); mConversationArrayAdapter.add(mConnectedDeviceName+": " + readMessage); break; case MESSAGE_DEVICE_NAME: // save the connected device's name mConnectedDeviceName = msg.getData().getString(DEVICE_NAME); Toast.makeText(getApplicationContext(), "Connected to " + mConnectedDeviceName, Toast.LENGTH_SHORT).show(); break; case MESSAGE_TOAST: Toast.makeText(getApplicationContext(), msg.getData().getString(TOAST), Toast.LENGTH_SHORT).show(); break; } } };
2. 主UI中初始化BluetoothChatService的实例，并在初始化时将mHandler作参数传递给实例：
private void setupChat() { Log.d(TAG, "setupChat()"); // Initialize the array adapter for the conversation thread mConversationArrayAdapter = new ArrayAdapter<String>(this, R.layout.message); mConversationView = (ListView) findViewById(R.id.in); mConversationView.setAdapter(mConversationArrayAdapter); // Initialize the compose field with a listener for the return key mOutEditText = (EditText) findViewById(R.id.edit_text_out); mOutEditText.setOnEditorActionListener(mWriteListener); // Initialize the send button with a listener that for click events mSendButton = (Button) findViewById(R.id.button_send); mSendButton.setOnClickListener(new OnClickListener() { public void onClick(View v) { // Send a message using content of the edit text widget TextView view = (TextView) findViewById(R.id.edit_text_out); String message = view.getText().toString(); sendMessage(message); } }); // Initialize the BluetoothChatService to perform bluetooth connections mChatService = new BluetoothChatService(this, mHandler); // Initialize the buffer for outgoing messages mOutStringBuffer = new StringBuffer(""); }
3. 主UI中定义事件响应函数(发送按钮)，其中调用sendMessage函数：
// Initialize the send button with a listener that for click events mSendButton = (Button) findViewById(R.id.button_send); mSendButton.setOnClickListener(new OnClickListener() { public void onClick(View v) { // Send a message using content of the edit text widget TextView view = (TextView) findViewById(R.id.edit_text_out); String message = view.getText().toString(); sendMessage(message); } });
4. sendMessage函数中，调用功能类BluetoothChatService.java的子函数：
/** * Sends a message. * @param message A string of text to send. */ private void sendMessage(String message) { // Check that we're actually connected before trying anything if (mChatService.getState() != BluetoothChatService.STATE_CONNECTED) { Toast.makeText(this, R.string.not_connected, Toast.LENGTH_SHORT).show(); return; } // Check that there's actually something to send if (message.length() > 0) { // Get the message bytes and tell the BluetoothChatService to write byte[] send = message.getBytes(); mChatService.write(send); // Reset out string buffer to zero and clear the edit text field mOutStringBuffer.setLength(0); mOutEditText.setText(mOutStringBuffer); } }
注意这里的mChatSercice.write(send)函数，出于线程安全的考虑，在BluetoothChatService.java中是这么定义的：
/** * Write to the ConnectedThread in an unsynchronized manner * @param out The bytes to write * @see ConnectedThread#write(byte[]) */ public void write(byte[] out) { // Create temporary object ConnectedThread r; // Synchronize a copy of the ConnectedThread synchronized (this) { if (mState != STATE_CONNECTED) return; r = mConnectedThread; } // Perform the write unsynchronized r.write(out); }
这里定义了一个临时线程类ConnectedThread r，而这个线程类的定义如下：
/** * This thread runs during a connection with a remote device. * It handles all incoming and outgoing transmissions. */ private class ConnectedThread extends Thread { private final BluetoothSocket mmSocket; private final InputStream mmInStream; private final OutputStream mmOutStream; public ConnectedThread(BluetoothSocket socket, String socketType) { Log.d(TAG, "create ConnectedThread: " + socketType); mmSocket = socket; InputStream tmpIn = null; OutputStream tmpOut = null; // Get the BluetoothSocket input and output streams try { tmpIn = socket.getInputStream(); tmpOut = socket.getOutputStream(); } catch (IOException e) { Log.e(TAG, "temp sockets not created", e); } mmInStream = tmpIn; mmOutStream = tmpOut; } public void run() { Log.i(TAG, "BEGIN mConnectedThread"); byte[] buffer = new byte[1024]; int bytes; // Keep listening to the InputStream while connected while (true) { try { // Read from the InputStream bytes = mmInStream.read(buffer); // 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(); // Start the service over to restart listening mode BluetoothChatService.this.start(); break; } } } /** * Write to the connected OutStream. * @param buffer The bytes to write */ public void write(byte[] buffer) { try { mmOutStream.write(buffer); // Share the sent message back to the UI Activity mHandler.obtainMessage(BluetoothChat.MESSAGE_WRITE, -1, -1, buffer).sendToTarget(); } catch (IOException e) { Log.e(TAG, "Exception during write", e); } } public void cancel() { try { mmSocket.close(); } catch (IOException e) { Log.e(TAG, "close() of connect socket failed", e); } } }
从write()函数的定义中可以看到，mHandler.obtainMessage(BluetoothChat.MESSAGE_WRITE, -1, -1, buffer) .sendToTarget()实现了线程和主UI之间的通信。