Hold a Bluetooth connection with a few steps

Question

I am creating an Android application that communicates with the Arduino board via bluetooth, I have a Bluetooth code in my class called BlueComms. To connect to the device, I use the following method:

public boolean connectDevice() { CheckBt(); BluetoothDevice device = mBluetoothAdapter.getRemoteDevice(address); Log.d(TAG, "Connecting to ... " + device); mBluetoothAdapter.cancelDiscovery(); try { btSocket = device.createRfcommSocketToServiceRecord(MY_UUID); btSocket.connect(); outStream = btSocket.getOutputStream(); Log.d(TAG, "Connection made."); return true; } catch (IOException e) { try { btSocket.close(); } catch (IOException e2) { Log.d(TAG, "Unable to end the connection"); return false; } Log.d(TAG, "Socket creation failed"); } return false; } private void CheckBt() { mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter(); if (!mBluetoothAdapter.isEnabled()) { System.out.println("Bt dsbld"); } if (mBluetoothAdapter == null) { System.out.println("Bt null"); } } 

This connection is fine, but as soon as I leave the activity with which I connected, it disconnects the connection, showing it through LogCat,

  D/dalvikvm(21623): GC_CONCURRENT freed 103K, 10% free 2776K/3056K, paused 5ms+2ms, total 35ms 

I can no longer connect to the device, but if I call killBt (), it causes a fatal error, and if I try to send data, I get a "Socket Error" error message. My message code is sent as follows:

 public void sendData(String data, int recvAct) { try { outStream = btSocket.getOutputStream(); } catch (IOException e) { Log.d(TAG, "Bug BEFORE Sending stuff", e); } String message = data; byte[] msgBuffer = message.getBytes(); try { outStream.write(msgBuffer); } catch (IOException e) { Log.d(TAG, "Bug while sending stuff", e); } } 

How should I prevent the connection from being suspended by the activity that I connect to, when I switch another action, I switch the actions with this code:

 Intent myIntent = new Intent(v.getContext(), Timelapse.class); startActivityForResult(myIntent, 0); 

Thanks a lot Rozz

Answer 1

Where did you save the instance of the BlueComms class? If you put it in the first action, then the class instance would be killed when this activity was destroyed, when you left it, and move to the next action (NB actions will also be destroyed when the screen rotates).

So, you need to find a way to keep the BlueComms class instance alive as long as you need it. You can pass it between actions through public properties and save them in the included onRetainNonConfigurationInstance () during rotation.

An easier way is to create a class that extends Application , use it as an application delegate for your application, and add a public property to it to store an instance of the BlueComms class inside it. Thus, an instance of the BlueComms class will be available for the life of your application.

Expand application

 import android.app.Application; public class cBaseApplication extends Application { public BlueComms myBlueComms; @Override public void onCreate() { super.onCreate(); myBlueComms = new BlueComms(); } } 

Make your class an application delegate in the application manifest

 <application android:name="your.app.namespace.cBaseApplication" android:icon="@drawable/icon" android:label="@string/app_name" > 

Access to the base application from any of your actions like this

 ((cBaseApplication)this.getApplicationContext()).myBlueComms.SomeMethod(); 

Answer 2

What I did was create a singleton class for BluetoothConnection. Therefore, the creation of sockets occurs only once.

When the onCreate method of any activity is created, it first retrieves an instance of the BluetoothConnection class.

The handler is used to send messages from the stream in the BluetoothConnection class to the corresponding operation using the settings handler.

how

 Class MyBTConnection{ private static MyBTConnection connectionObj; private Handler mHandler; public MyBTConnection() { //constructor } public static MyBTConnection getInstance() { if(connectionObj == null) { connectionObj = new MyBTConnection(); } return connectionObj; } } public void setHandler(Handler handler) { mHandler = handler; } ..... Code for Bluetooth Connection .... to send message : mHandler.obtainMessage(what).sendToTarget(); } // in first activity class MainActivity extends Activity { private MyBTConnection connectionObj; public onCreate(....) { /* * Since this is first call for getInstance. A new object * of MyBTConnection will be created and a connection to * remote bluetooth device will be established. */ connectionObj = MyBTConnection.getInstance(); connectionObj.setHandler(mHandler); } private Handler mHandler = new Handler(){ public void onReceive(...) { /// handle received messages here } }; } // in second activity class SecondActivity extends Activity { private MyBTConnection connectionObj; public onCreate(....) { /* * Since this is second call for getInstance. * Object for MyBTConnection was already created in previous * activity. So getInstance will return that previously * created object and in that object, connection to remote * bluetooth device is already established so you can * continue your work here. */ connectionObj = MyBTConnection.getInstance(); connectionObj.setHandler(mHandler); } private Handler mHandler = new Handler(){ public void onReceive(...) { /// handle received messages here } }; } 

Answer 3

When you select a device to connect to, and when you click on the device list item to request a connection to the device, use AsyncTask and place the connect method inside AsyncTask as follows: -

  AsyncTask.execute(new Runnable() { @Override public void run() { try { bluetoothSocket = Globals.bluetoothDevice.createRfcommSocketToServiceRecord(Globals.DEFAULT_SPP_UUID); bluetoothSocket.connect(); // After successful connect you can open InputStream } catch (IOException e) { e.printStackTrace(); } **Here is the full code for the same problem that i have cracked :-** listView.setOnItemClickListener(new AdapterView.OnItemClickListener() { @Override public void onItemClick(AdapterView<?> parent, View view, int position, long id) { lablelexconnected.setText("Connecting ..."); bdDevice = arrayListBluetoothDevices.get(position); //bdClass = arrayListBluetoothDevices.get(position) // Toast.makeText(getApplicationContext()," " + bdDevice.getAddress(),Toast.LENGTH_SHORT).show(); Log.i("Log", "The dvice : " + bdDevice.toString()); bdDevice = bluetoothAdapter.getRemoteDevice(bdDevice.getAddress()); Globals.bluetoothDevice = bluetoothAdapter.getRemoteDevice(bdDevice.getAddress()); System.out.println("Device in GPS Settings : " + bdDevice); // startService(new Intent(getApplicationContext(),MyService.class)); /* Intent i = new Intent(GpsSettings.this, MyService.class); startService(i);*/ // finish(); // connectDevice(); AsyncTask.execute(new Runnable() { @Override public void run() { try { bluetoothSocket = Globals.bluetoothDevice.createRfcommSocketToServiceRecord(Globals.DEFAULT_SPP_UUID); bluetoothSocket.connect(); // After successful connect you can open InputStream InputStream in = null; in = bluetoothSocket.getInputStream(); InputStreamReader isr = new InputStreamReader(in); br = new BufferedReader(isr); while (found == 0) { String nmeaMessage = br.readLine(); Log.d("NMEA", nmeaMessage); // parse NMEA messages sentence = nmeaMessage; System.out.println("Sentence : " + sentence); if (sentence.startsWith("$GPRMC")) { String[] strValues = sentence.split(","); System.out.println("StrValues : " + strValues[3] + " " + strValues[5] + " " + strValues[8]); if (strValues[3].equals("") && strValues[5].equals("") && strValues[8].equals("")) { Toast.makeText(getApplicationContext(), "Location Not Found !!! ", Toast.LENGTH_SHORT).show(); } else { latitude = Double.parseDouble(strValues[3]); if (strValues[4].charAt(0) == 'S') { latitude = -latitude; } longitude = Double.parseDouble(strValues[5]); if (strValues[6].charAt(0) == 'W') { longitude = -longitude; } course = Double.parseDouble(strValues[8]); // Toast.makeText(getApplicationContext(), "latitude=" + latitude + " ; longitude=" + longitude + " ; course = " + course, Toast.LENGTH_SHORT).show(); System.out.println("latitude=" + latitude + " ; longitude=" + longitude + " ; course = " + course); // found = 1; NMEAToDecimalConverter(latitude, longitude); } } } } catch (IOException e) { e.printStackTrace(); } } }); } }); 

Answer 4

I currently have exactly the same problem, and I was thinking of opening / closing a Bluetooth socket every time an Activity requests it. Each action has its own copy of BlueComms.

Since my application will become a bit complicated, and Bluetooth-enabled requests from various activities will appear, I think this method will become very difficult to use and troubleshoot.

Another way I came across while reading here ... https://developer.android.com/guide/components/services.html

A service can be created in the background, which always has a Bluetooth connector. All Bluetooth requests can be made using Intent for this service. It also creates some significant complexity, but feels a lot more neat and organized.

I currently have this dilemma: either use a thread for each action, or use a service. I do not know which way is actually better.