Can't display a list of visible nearby Bluetooth devices

[Shakku Singh]

Hi everyone.
So I'm trying to display a list of visible bluetooth devices but it's not working unless I hit refresh in the device's bluetooth manager, and then its showing the same device name and address multiple times.

Here's the main activity code

package com.apps.lenovo.bluetoothdevices;

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.le.BluetoothLeScanner;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    BroadcastReceiver mReceiver;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        if(bluetoothAdapter!=null) {
            final TextView msg=(TextView)findViewById(R.id.msg);
            final ListView visibleDevices=(ListView)findViewById(R.id.Visibledevices);
            final List<String> devices=new ArrayList<String>();
            mReceiver = new BroadcastReceiver() {
                public void onReceive(Context context, Intent intent) {
                    String action = intent.getAction();
                    if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                        BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                        String deviceInfo=device.getName() + "\n" + device.getAddress();
                        boolean isThere=false;
                        for(String aDevice: devices)
                            if(aDevice.equals(deviceInfo))
                                isThere=true;
                        if(!isThere)
                            devices.add(deviceInfo);
                        visibleDevices.setAdapter(new ArrayAdapter<String>(context, android.R.layout.simple_list_item_1, devices));
                    }
                }
            };
            IntentFilter filter = new IntentFilter();
            filter.addAction(BluetoothDevice.ACTION_FOUND);
            this.registerReceiver(mReceiver, filter);
            bluetoothAdapter.enable();
            if(bluetoothAdapter.isDiscovering())
                bluetoothAdapter.cancelDiscovery();
            bluetoothAdapter.startDiscovery();
            if(bluetoothAdapter.isDiscovering()) {
                msg.setText("discovering");
            }
        }
    }
    @Override
    public void onDestroy() {
        super.onDestroy();
        this.unregisterReceiver(this.mReceiver);
    }
}

And here's the manifest file code

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.apps.lenovo.bluetoothdevices">
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
    <uses-permission android:name="android.permission.BLUETOOTH" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

And the layout code

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.apps.lenovo.bluetoothdevices.MainActivity">

    <TextView
        android:id="@+id/msg"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <ListView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/msg"
        android:id="@+id/Visibledevices"
        android:layout_centerVertical="true"
        android:layout_alignParentStart="true" />
</RelativeLayout>

To make sure startDiscovery() was working properly I added a TextView that shows a message when the device is discovering, but that's not displaying anything either unless I hit refresh.

[Chris Barrett]

Hi Shakku,

Welcome to the Ranch!

I have not tried compiling your program, but I'm curious to know about this part:

boolean isThere=false;
for(String aDevice: devices)
   if(aDevice.equals(deviceInfo))
      isThere=true;
   if(!isThere)
      devices.add(deviceInfo);

Why is that part needed?  It seems to be overly complex and the lack of {} makes following the blocks difficult.

[Shakku Singh]

Chris Barrett wrote:Hi Shakku,

Welcome to the Ranch!

I have not tried compiling your program, but I'm curious to know about this part:

boolean isThere=false;
for(String aDevice: devices)
   if(aDevice.equals(deviceInfo))
      isThere=true;
   if(!isThere)
      devices.add(deviceInfo);

Why is that part needed?  It seems to be overly complex and the lack of {} makes following the blocks difficult.

Hi Chris
I was just trying to make sure that entries in the list are not repeated, although its not working.

[Dave Tolls]

For starters I'd stick some logging in there to try and trace what's going on.

The BluetoothAdapter should only send a FOUND for each device once, so logging might help to show whether that is the case or not.

Remove the check for whether the device is already in the list, since that should not be needed.
Also you should not have to manually get your android device to search.  If you do that then yes, you may well get duplicates.

Can you register for the START and STOP events from the adapter as well?  Log them just to track things.
That might give you some more info.

[Shakku Singh]

Dave Tolls wrote:For starters I'd stick some logging in there to try and trace what's going on.

The BluetoothAdapter should only send a FOUND for each device once, so logging might help to show whether that is the case or not.

Remove the check for whether the device is already in the list, since that should not be needed.
Also you should not have to manually get your android device to search.  If you do that then yes, you may well get duplicates.

Can you register for the START and STOP events from the adapter as well?  Log them just to track things.
That might give you some more info.

So, as you advised, I used logging, removed the check for device repetition and added the START and STOP action to the intent filter, but I'm getting the same results.
Here's the modified code

package com.apps.lenovo.pettalk_raw2;

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
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.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    BroadcastReceiver mReceiver;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        if(bluetoothAdapter!=null) {
            bluetoothAdapter.enable();
            TextView msg=(TextView)findViewById(R.id.msg);
            final ListView visibleDevices=(ListView)findViewById(R.id.Visibledevices);
            final List<String> devices= new ArrayList<>();
            mReceiver = new BroadcastReceiver() {
                public void onReceive(Context context, Intent intent) {
                    String action = intent.getAction();
                    if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                        BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                        String deviceInfo=device.getName() + "\n" + device.getAddress();
                        devices.add(deviceInfo);
                        visibleDevices.setAdapter(new ArrayAdapter<String>(context, android.R.layout.simple_list_item_1, devices));
                        Log.i("In action_found", "A device found");
                    }
                    else if(BluetoothAdapter.ACTION_DISCOVERY_STARTED.equals(action)) {
                        Log.i("In discovery started", "Discovery started");
                    }
                    else if(BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
                        Log.i("In discovery finished", "Discovery finished");
                    }
                }
            };

            IntentFilter filter = new IntentFilter();
            filter.addAction(BluetoothDevice.ACTION_FOUND);
            filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_STARTED);
            filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
            this.registerReceiver(mReceiver, filter);
            if(bluetoothAdapter.isEnabled())
                Log.i("Status", "Bluetooth enabled");
            if(bluetoothAdapter.isDiscovering())
                bluetoothAdapter.cancelDiscovery();
            bluetoothAdapter.startDiscovery();
            if(bluetoothAdapter.isDiscovering()) {
                msg.setText("discovering");
            }

        }
    }
    @Override
    public void onDestroy() {
        super.onDestroy();
        this.unregisterReceiver(this.mReceiver);
    }
}

I tested it on Lollipop and Jelly Bean platform and on both I have to manually scan for devices, after which I'm getting proper logging messages, although, on Lollipop the devices are repeating, generating log message every time a device is added to the list, whereas on Jelly Bean one device is displayed only once.
Another thing that I don't understand is that the two conditions

if(bluetoothAdapter.isEnabled())

and

if(bluetoothAdapter.isDiscovering())

are not being satisfied as I'm neither getting the log message nor anything on the TextView.

[Shakku Singh]

So i finally figured out what the problem was.
I needed to add a listener to track the state of the Bluetooth adapter. I was calling the startDiscovery() method but it was not synchronized with the enable() method call, therefore I had to start the discovery manually.

package com.apps.lenovo.pettalk_raw1;

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
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.widget.ArrayAdapter;
import android.widget.CompoundButton;
import android.widget.ListView;
import android.widget.Switch;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
    ListView visibleDevices;
    Switch bluetoothSwitch;
    private BroadcastReceiver blueReceiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        visibleDevices = (ListView) findViewById(R.id.visibleDevices);
        bluetoothSwitch = (Switch) findViewById(R.id.bluetoothSwitch);
        if (bluetoothAdapter != null) {
            if (bluetoothAdapter.isEnabled()) {
                bluetoothSwitch.setChecked(true);
                bluetoothAdapter.startDiscovery();
            }
            final ArrayList<String> devices = new ArrayList<>();
            final ArrayAdapter<String> theAdapter = new ArrayAdapter<>(getBaseContext(), android.R.layout.simple_list_item_1, devices);
            visibleDevices.setAdapter(theAdapter);
            blueReceiver = new BroadcastReceiver() {
                @Override
                public void onReceive(Context context, Intent intent) {
                    String action = intent.getAction();
                    if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
                        int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, BluetoothAdapter.ERROR);
                        if (state == BluetoothAdapter.STATE_ON) {
                            bluetoothAdapter.startDiscovery();
                            bluetoothSwitch.setChecked(true);
                        } else if (state == BluetoothAdapter.STATE_OFF) {
                            devices.clear();
                            theAdapter.notifyDataSetChanged();
                            bluetoothSwitch.setChecked(false);
                        }
                    }
                    else if(BluetoothDevice.ACTION_FOUND.equals(action)) {
                        Boolean repeated = false;
                        BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                        String deviceInfo = device.getName() + "\n" + device.getAddress();
                        for (String x : devices) {
                            if (x.equals(deviceInfo)) {
                                repeated = true;
                                break;
                            }
                        }
                        if (!repeated)
                            devices.add(deviceInfo);
                        theAdapter.notifyDataSetChanged();
                    }
                    else if(BluetoothAdapter.ACTION_DISCOVERY_STARTED.equals(action))
                        devices.clear();
                }
            };
            bluetoothSwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
                @Override
                public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                    if (isChecked) {
                        bluetoothAdapter.enable();
                    } else {
                        bluetoothAdapter.disable();
                    }
                }
            });
        }
        IntentFilter filter = new IntentFilter();
        filter.addAction(BluetoothAdapter.ACTION_STATE_CHANGED);
        filter.addAction(BluetoothDevice.ACTION_FOUND);
        filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_STARTED);
        registerReceiver(blueReceiver, filter);
    }
    @Override
    public void onDestroy() {
        super.onDestroy();
        unregisterReceiver(blueReceiver);
    }
}