[Android Q&A, Help & Troubleshooting] romo1987:
I'm programming a simple Bluetooth client to send and receive text messages throught RFCOMM as a serial port. I had a look at the Android SDK tutorials and did it in the same way: an Activity which calls a thread to make the connection, and once done, another thread to take care of msg reception.

I'm trying to connect to a Parallax EasyBluetooth. Connection works all right between computer and EasyBT, and also between a Java based mobile and the EasyBT. So the problem must be at the code or, I hope not, at the Android mobile bluetooth chip. Anyway it gets on and off, and detects other devices when scanning, so I guess problem is just my coding.

The problem is that the code gets stuck at the connect() method. So let's see if anyone knows why.

The XML for the activity is simple:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello"
/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/boton"
android:id="@+id/boton_enviar"
/>
</LinearLayout>

Of course I have added the bluetooth permissions to the Manifiest:

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

And the code is the following:

package uniovi.PFC;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.UUID;

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;

public class PruebaBTActivity extends Activity {
private String TAG = "pruebaBT";
private BluetoothAdapter mBluetoothAdapter;
private Map<String, BluetoothDevice> mArrayAdapter;
private ConnectedThread hiloEscuchas;
private ConnectThread hiloConectando;
private Handler mHandler;
private Button botonEnviar;
private static final UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
private static final int REQUEST_ENABLE_BT = 1;
private static final int MESSAGE_READ = 1;
private byte bytes_enviar[];
private String cmd;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Log.d(TAG, "On create abriendo");

mArrayAdapter = new HashMap<String, BluetoothDevice>();

botonEnviar = (Button)findViewById(R.id.boton_enviar);
botonEnviar.setEnabled(false);
botonEnviar.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
cmd = "A";
bytes_enviar = cmd.getBytes();
hiloEscuchas.write(bytes_enviar);
}
});
Log.d(TAG, "On create cerrando");
}

@Override

public void onResume() {
super.onResume();
mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
if (mBluetoothAdapter == null) {
Log.d(TAG, "Device does not support Bluetooth");
}
if (!mBluetoothAdapter.isEnabled()) {
Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}

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.put(device.getName(), device);
}
}

BluetoothDevice device = mArrayAdapter.get("EasyBT");
hiloConectando = new ConnectThread(device);
hiloConectando.run();
//while(hiloEscuchas.isConnected()==false);
//botonEnviar.setEnabled(true);
}

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)
hiloEscuchas = new ConnectedThread(mmSocket);
hiloEscuchas.run();
}

/** Will cancel an in-progress connection, and close the socket */
public void cancel() {
try {
mmSocket.close();
} catch (IOException e) { }
}
}

private class ConnectedThread extends Thread {
private final BluetoothSocket mmSocket;
private final InputStream mmInStream;
private final OutputStream mmOutStream;
private boolean conectado;

public ConnectedThread(BluetoothSocket socket) {
mmSocket = socket;
InputStream tmpIn = null;
OutputStream tmpOut = null;
conectado = false;
mHandler = new Handler();

// 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;
conectado = true;
}

public boolean isConnected(){
return conectado;
}

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 {

cmd = "A";
bytes_enviar = cmd.getBytes();
hiloEscuchas.write(bytes_enviar);
// 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) { }

}
}
}

There was some code to make a bluetooth scan for devices, but in order to get things simple until it works, I wrote the MAC address manually into a variable. Comments explain this, and also shows where it gets stuck.

Thanks