Connecting 2 bluetooth devices

Question

I'm trying to make an application that is using bluetooth.It's very simple but I'm stuck at connecting devices.

So far I've made 2 listviews, one is displaying paired devices and the other found devices.I dont understand how sockets work and how to make the device server or a client.

Can someone please explain me that or at least tell me what to do with the code I already made(copied).

I've gone through all the tutorials I could find and I still dont understand it.The bluetooth chat example is very confusing, I'm a beginner in android programming and didn't really study much java.

This is the code:

public class ConnectThread extends Thread{
        BluetoothDevice device;
        private BluetoothSocket socket;

        ConnectThread(){
            connect(device, MY_UUID);
        }
        public boolean connect(BluetoothDevice bTDevice, UUID mUUID) {
            BluetoothSocket temp = null;
            try {
                temp = bTDevice.createRfcommSocketToServiceRecord(mUUID);
            } catch (IOException e) {
                Log.d("CONNECTTHREAD","Could not create RFCOMM socket:" + e.toString());
                return false;
            }
            try {
                socket.connect();
            } catch(IOException e) {
                Log.d("CONNECTTHREAD","Could not connect: " + e.toString());
                try {
                    socket.close();
                } catch(IOException close) {
                    Log.d("CONNECTTHREAD", "Could not close connection:" + e.toString());
                    return false;
                }
            }
            return true;
        }

        public boolean cancel() {
            try {
                socket.close();
            } catch(IOException e) {
                Log.d("CONNECTTHREAD","Could not close connection:" + e.toString());
                return false;
            }
            return true;
        }
    }
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 = bluetooth.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)
                   try {
                       mmServerSocket.close();
                   } catch (IOException e) {
                       e.printStackTrace();
                   }
                   break;
               }
           }
       }

       /** Will cancel the listening socket, and cause the thread to finish */
       public void cancel() {
           try {
               mmServerSocket.close();
           } catch (IOException e) { }
       }}

This is the xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:orientation="horizontal"
        android:layout_weight="1"
        android:baselineAligned="false">
    <ListView
        android:layout_width="170dp"
        android:layout_height="fill_parent"
        android:layout_gravity="start"
        android:background="@drawable/lviewbg"
        android:id="@+id/paired_devies">
    </ListView>
        <ListView
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_gravity="fill_horizontal"
            android:background="@drawable/lviewbg"
            android:id="@+id/new_devices">
        </ListView>
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="50dp">
    <Button
        android:id="@+id/discover"
        android:layout_width="0dp"
        android:layout_height="50dp"
        android:layout_weight="1"
        android:background="#aa0000ff"
        android:text="@string/disc"
        style="?android:attr/buttonBarButtonStyle"
        />
    <Button
        android:layout_width="0dp"
        android:layout_height="50dp"
        android:layout_weight="1"
        android:background="#aa0000ff"
        android:text="@string/discoverable"
        android:onClick="makeDiscoverable"
        style="?android:attr/buttonBarButtonStyle"
        />
    </LinearLayout>
</LinearLayout>

This is rest of the code if you need it:

package com.example.user.broj;

    import android.app.Activity;
    import android.bluetooth.BluetoothAdapter;
    import android.bluetooth.BluetoothDevice;
    import android.bluetooth.BluetoothServerSocket;
    import android.bluetooth.BluetoothSocket;
    import android.content.BroadcastReceiver;
    import android.content.Context;
    import android.content.Intent;
    import android.content.IntentFilter;
    import android.os.Bundle;
    import android.support.v7.app.AppCompatActivity;
    import android.util.Log;
    import android.view.View;
    import android.widget.AdapterView;
    import android.widget.ArrayAdapter;
    import android.widget.Button;
    import android.widget.ListView;
    import android.widget.TextView;
    import android.widget.Toast;

    import java.io.IOException;
    import java.util.Set;
    import java.util.UUID;

    public class BluetoothDevices extends AppCompatActivity{

        private static final String TAG = "DeviceListActivity";
        private static final boolean D = true;

        BluetoothDevice device;

        static int REQUEST_ENABLE_BT = 1;
        static int DISCOVERABLE_BT_REQUEST_CODE = 1;
        static int DISCOVERABLE_DURATION = 120;
        public static String EXTRA_DEVICE_ADDRESS = "device_address";
        private BluetoothAdapter bluetooth = BluetoothAdapter.getDefaultAdapter();
        ArrayAdapter<String> mPairedDevicesArrayAdapter;
        private ArrayAdapter<String> mNewDevicesArrayAdapter;
    //This is used for connecting devices
        static final String NAME = "BluetoothGame";
        static final UUID MY_UUID = UUID.fromString("ae19c8fa-9b60-11e5-8994-feff819cdc9f");

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.start);
            Button scanButton = (Button) findViewById(R.id.discover);
            scanButton.setOnClickListener(new View.OnClickListener() {
                public void onClick(View view) {
                    doDiscovery();
                    view.setClickable(false);
                }
            });
    //enabling bluetooth
            if(!bluetooth.isEnabled()){
                Intent btIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
                startActivityForResult(btIntent, REQUEST_ENABLE_BT);
            }
    //arrayadapters for paired and new devices list views
            mPairedDevicesArrayAdapter = new ArrayAdapter<>(this, R.layout.device_name);
            mNewDevicesArrayAdapter = new ArrayAdapter<>(this, R.layout.device_name);
    //listview for paired devices
            ListView deviceList = (ListView) findViewById(R.id.paired_devies);
            deviceList.setAdapter(mPairedDevicesArrayAdapter);
            deviceList.setOnItemClickListener(mDeviceClickListener);
    //listview for new devices
            ListView newDevicesListView = (ListView) findViewById(R.id.new_devices);
            newDevicesListView.setAdapter(mNewDevicesArrayAdapter);
            newDevicesListView.setOnItemClickListener(mDeviceClickListener);

            IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
            this.registerReceiver(mReceiver, filter);

            filter = new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
            this.registerReceiver(mReceiver, filter);

            bluetooth = BluetoothAdapter.getDefaultAdapter();

            Set<BluetoothDevice> pairedDevices = bluetooth.getBondedDevices();

            if (pairedDevices.size() > 0) {
                //findViewById(R.id.title_paired_devices).setVisibility(View.VISIBLE);
                for (BluetoothDevice device : pairedDevices) {
                    mPairedDevicesArrayAdapter.add(device.getName() + "\n" + device.getAddress());
                }
            } else {
                String noDevices = getResources().getText(R.string.none_paired).toString();
                mPairedDevicesArrayAdapter.add(noDevices);
            }
        }
    //button onClick for making the device discoverable
        public void makeDiscoverable(View view) {
            Intent discoverableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
            discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, DISCOVERABLE_DURATION);
            startActivityForResult(discoverableIntent, DISCOVERABLE_BT_REQUEST_CODE);
        }

        @Override
        protected void onActivityResult(int requestCode, int resultCode, Intent data) {
            if (requestCode == DISCOVERABLE_BT_REQUEST_CODE){
                if (resultCode == DISCOVERABLE_DURATION){
                    Toast.makeText(getApplicationContext(), "Your device is now discoverable by other devices for " +
                                    DISCOVERABLE_DURATION + " seconds",
                            Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(getApplicationContext(), "Fail to enable discoverability on your device.",
                            Toast.LENGTH_SHORT).show();
                }
            }
        }

        @Override
        protected void onDestroy() {
            super.onDestroy();
            // Make sure we're not doing discovery anymore
            if (bluetooth != null) {
                bluetooth.cancelDiscovery();
            }
            // Unregister broadcast listeners
            this.unregisterReceiver(mReceiver);
        }

        private void doDiscovery() {
            if (D) Log.d(TAG, "doDiscovery()");
            // Indicate scanning in the title
            setProgressBarIndeterminateVisibility(true);
            setTitle(R.string.scanning);
            // Turn on sub-title for new devices
            // findViewById(R.id.title_new_devices).setVisibility(View.VISIBLE);
            // If we're already discovering, stop it
            if (bluetooth.isDiscovering()) {
                bluetooth.cancelDiscovery();
            }
            // Request discover from BluetoothAdapter
            bluetooth.startDiscovery();
        }

        private AdapterView.OnItemClickListener mDeviceClickListener = new AdapterView.OnItemClickListener() {
            public void onItemClick(AdapterView<?> av, View v, int arg2, long arg3) {
                // Cancel discovery because it's costly and we're about to connect
                bluetooth.cancelDiscovery();
                // Get the device MAC address, which is the last 17 chars in the View
                String info = ((TextView) v).getText().toString();
                String address = info.substring(info.length() - 17);
                // Create the result Intent and include the MAC address
                Intent intent = new Intent();
                intent.putExtra(EXTRA_DEVICE_ADDRESS, address);
                // Set result and finish this Activity
                setResult(Activity.RESULT_OK, intent);
                finish();
            }
        };

        private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                Button scanButton = (Button) findViewById(R.id.discover);
                String action = intent.getAction();
                // When discovery finds a device
                if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                    // Get the BluetoothDevice object from the Intent
                     device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                    // If it's already paired, skip it, because it's been listed already
                    if (device.getBondState() != BluetoothDevice.BOND_BONDED) {
                        mNewDevicesArrayAdapter.add(device.getName() + "\n" + device.getAddress());
                    }
                    // When discovery is finished, change the Activity title
                } else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
                    setProgressBarIndeterminateVisibility(false);
                    setTitle(R.string.select_device);
                    scanButton.setClickable(true);
                    if (mNewDevicesArrayAdapter.getCount() == 0) {
                        String noDevices = getResources().getText(R.string.none_found).toString();
                        mNewDevicesArrayAdapter.add(noDevices);
                    }
                }
            }
        };
    }

Answer 1

Async class for connection via Bluetoothsocket

UUID SERIAL_UUID = UUID.fromString("00001101-0000-1000-8000-00805f9b34fb");
InputStream is1;
OutputStream os1;
BluetoothAdapter bluetoothAdapter = null;
BluetoothSocket socket = null; 

class UserInterface extends Thread {
BluetoothDevice bdDevice;
public UserInterface() {
    bdDevice = your pair device;

}

@Override
public void run() {
    Looper.prepare();
    try {

        BluetoothDevice device = bluetoothAdapter.getRemoteDevice(bdDevice.getAddress());

        if (socket != null && socket.isConnected()) {
            is1.close();
            os1.close();
            socket.close();

        }
        try {
            socket = device.createInsecureRfcommSocketToServiceRecord(SERIAL_UUID);
        } catch (Exception e) {
            Log.e("", "Error creating socket");
        }
        if (bluetoothAdapter.isDiscovering()) {
            bluetoothAdapter.cancelDiscovery();
        }


        try {
            socket.connect();
            Log.e("", "Connected Rfcomm");

        } catch (IOException e) {
            Log.e("", e.getMessage());
            try {
                Log.e("", "trying fallback...");

                socket = device.createInsecureRfcommSocketToServiceRecord(SERIAL_UUID);
                socket.connect();
                Log.e("", "Connected serial UDID");

            } catch (Exception e2) {
                Log.e("", "Couldn't establish Bluetooth connection!");
            }
        }


        if (socket.isConnected()) {
           // dismiss Progress Dialog
                os1 = socket.getOutputStream();
                is1 = socket.getInputStream();
                Log.i("TAG", "Socket Connected");
           //code after socket connect

        } else {
            // dismiss Progress Dialog
            showProgressDialogToast("Please restart bluetooth Device");
            closeSocket();
            Log.i("TAG", "Socket Disconnected");
        }

        Log.i("Log", "Removed" + bdDevice.getName());
    } catch (Exception e) {
        // TODO Auto-generated catch block
        Log.i("Log", "Under Catch of thread");
        e.printStackTrace();
        // dismiss Progress Dialog
    }
}
}

use Thread class like this

UserInterface userInterface = new UserInterface();
userInterface.start();

Answer 2

Basically refer the tutorial given by android developers on their site. In every connectivity there should be one server and one client. The server will just run the accept thread and the client will run the connect thread. Once the accept thread started, you need to connect from the client side with the proper device name.