Develop Reference

Scanning for bluetooth devices programmatically don't find anything in android 6+

I created an application which pairs a cellphone to a bluetooth module.
i tested this application with a 4.2 android cellphone and it worked quite well but in cellphones with android higher than 6 the device is not fidning anything when i press " Scan for new devices " button.
but when i go through my phone bluetooth itself, i can find the module i was looking for..
Bluetooth connection class :
public class BluetoothConnectionActivity extends AppCompatActivity {
private ProgressDialog mProgressDlg;
private ArrayList<BluetoothDevice> mDeviceList = new ArrayList<BluetoothDevice>();
private BluetoothAdapter mBluetoothAdapter;
BluetoothDevice device ;
private MediaPlayer mediaplayer = null ;
private Button bluetoothOnOff;
private Button viewpairedDevices;
private Button scanfornewDevices;
private Button blue2;
ImageView unMute;
View view1;
View view2;
private Activity context;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.bluetoothconnectionlayout);
bluetoothOnOff = (Button) findViewById(R.id.bluetoothOnOff);
viewpairedDevices = (Button) findViewById(R.id.viewpairedDevicesButton);
scanfornewDevices = (Button) findViewById(R.id.scanfornewDevicesButton);
blue2 = (Button) findViewById(R.id.bluetoothOnOff2);
view1 = findViewById(R.id.viewFader);
view2 = findViewById(R.id.viewFader2);
unMute = (ImageView) findViewById(R.id.settingStartupSecondary);
mediaplayer = MediaPlayer.create(getApplicationContext(),R.raw.sfxturnon);
Handler startup1 = new Handler();
startup1.postDelayed(new Runnable() {
#Override
public void run() {
view1.animate().alpha(1f).setDuration(500);
view2.animate().alpha(1f).setDuration(500);
}
},1000);
Handler startup2 = new Handler();
startup2.postDelayed(new Runnable() {
#Override
public void run() {
bluetoothOnOff.animate().alpha(1f).setDuration(500);
viewpairedDevices.animate().alpha(1f).setDuration(500);
scanfornewDevices.animate().alpha(1f).setDuration(500);
unMute.animate().alpha(1f).setDuration(100);
}
},1000);
//
// settingBtn.setOnClickListener(new View.OnClickListener() {
// #Override
// public void onClick(View view) {
//
//
// AudioManager amanager=(AudioManager)getSystemService(Context.AUDIO_SERVICE);
// amanager.setStreamMute(AudioManager.STREAM_NOTIFICATION, true);
//
//// settingBtn.setEnabled(false);
//// settingBtn.animate().alpha(0f);
//
// unMute.animate().alpha(1f);
// unMute.setEnabled(true);
//
//
// Toast.makeText(getApplicationContext(), " Application muted. ", Toast.LENGTH_SHORT).show();
//
//
// }
// });
Handler dawg = new Handler();
dawg.postDelayed(new Runnable() {
#Override
public void run() {
bluetoothOnOff.animate().alpha(1f).setDuration(1500);
viewpairedDevices.animate().alpha(1f).setDuration(2500);
scanfornewDevices.animate().alpha(1f).setDuration(3000);
}
},500);
mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
mProgressDlg = new ProgressDialog(this);
mProgressDlg.setMessage("Scanning, Please wait...");
mProgressDlg.setCancelable(false);
mProgressDlg.setButton(DialogInterface.BUTTON_NEGATIVE, "Cancel", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
mBluetoothAdapter.cancelDiscovery();
}
});}
if (mBluetoothAdapter.isEnabled()){
bluetoothOnOff.setText("Bluetooth is On");
blue2.setText("Bluetooth is On");
}else {
blue2.setText("Bluetooth is Off");
bluetoothOnOff.setText("Bluetooth is Off");
}
if (mBluetoothAdapter == null) {
showUnsupported();
} else {
viewpairedDevices.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();
if (pairedDevices == null || pairedDevices.size() == 0) {
Toast toast = Toast.makeText(getApplicationContext()," No paired device found.", Toast.LENGTH_SHORT);
View view3 = toast.getView();
view3.setBackgroundColor(Color.parseColor("#ffff5b"));
TextView text = (TextView) view3.findViewById(android.R.id.message);
text.setTextColor(Color.parseColor("#000000"));
toast.show();
} else {
ArrayList<BluetoothDevice> list = new ArrayList<BluetoothDevice>();
list.addAll(pairedDevices);
Intent intent = new Intent(BluetoothConnectionActivity.this, DeviceList.class);
intent.putParcelableArrayListExtra("device.list", list);
startActivity(intent);
}
}
});
scanfornewDevices.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View arg0) {
mBluetoothAdapter.startDiscovery();
}
});
bluetoothOnOff.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
if (mBluetoothAdapter.isEnabled()) {
mBluetoothAdapter.disable();
showDisabled();
bluetoothOnOff.setText("Bluetooth is OFF");
final Handler handler6 = new Handler();
handler6.postDelayed(new Runnable() {
#Override
public void run() {
mediaplayer.start();
}
}, 500);
final Handler handler3 = new Handler();
handler3.postDelayed(new Runnable() {
#Override
public void run() {
bluetoothOnOff.animate().translationY(-1f).setDuration(5000);
blue2.animate().translationY(-1f).setDuration(5000);
bluetoothOnOff.animate().alpha(1f).setDuration(3000);
blue2.animate().alpha(0f).setDuration(3000);
}
}, 500);
} else {
Intent intent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(intent, 1000);
}}
});
blue2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
if (mBluetoothAdapter.isEnabled()) {
mBluetoothAdapter.disable();
showDisabled();
bluetoothOnOff.setText("Bluetooth is OFF");
final Handler handler6 = new Handler();
handler6.postDelayed(new Runnable() {
#Override
public void run() {
mediaplayer.start();
}
}, 500);
final Handler handler3 = new Handler();
handler3.postDelayed(new Runnable() {
#Override
public void run() {
bluetoothOnOff.animate().translationY(-1f).setDuration(5000);
blue2.animate().translationY(-1f).setDuration(5000);
bluetoothOnOff.animate().alpha(1f).setDuration(3000);
blue2.animate().alpha(0f).setDuration(3000);
}
}, 500);
} else {
Intent intent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(intent, 1000);
}}
});
if (mBluetoothAdapter.isEnabled()) {
showEnabled();
} else {
showDisabled();
}
}
IntentFilter filter = new IntentFilter();
filter.addAction(BluetoothAdapter.ACTION_STATE_CHANGED);
filter.addAction(BluetoothDevice.ACTION_FOUND);
filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_STARTED);
filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
registerReceiver(mReceiver, filter);
}
#Override
public void onPause() {
if (mBluetoothAdapter != null) {
if (mBluetoothAdapter.isDiscovering()) {
mBluetoothAdapter.cancelDiscovery();
}
}
super.onPause();
}
#Override
public void onBackPressed() {
}
#Override
public void onDestroy() {
unregisterReceiver(mReceiver);
super.onDestroy();
}
private void showEnabled() {
bluetoothOnOff.setEnabled(true);
viewpairedDevices.setEnabled(true);
viewpairedDevices.setBackgroundResource(R.drawable.selectorstylish);
scanfornewDevices.setEnabled(true);
scanfornewDevices.setBackgroundResource(R.drawable.selectorstylish);
}
private void showDisabled() {
bluetoothOnOff.setEnabled(true);
viewpairedDevices.setEnabled(false);
viewpairedDevices.setBackgroundResource(R.drawable.selectorstylish);
scanfornewDevices.setEnabled(false);
scanfornewDevices.setBackgroundResource(R.drawable.selectorstylish);
}
private void showUnsupported() {
Toast toast = Toast.makeText(getApplicationContext()," Bluetooth is not supported by this device.", Toast.LENGTH_SHORT);
View view3 = toast.getView();
view3.setBackgroundColor(Color.parseColor("#ffff5b"));
TextView text = (TextView) view3.findViewById(android.R.id.message);
text.setTextColor(Color.parseColor("#000000"));
toast.show();
bluetoothOnOff.setEnabled(false);
viewpairedDevices.setEnabled(false);
viewpairedDevices.setBackgroundResource(R.drawable.selectorstylish);
scanfornewDevices.setEnabled(false);
scanfornewDevices.setBackgroundResource(R.drawable.selectorstylish);
}
private void showToast(String message) {
Toast.makeText(getApplicationContext(), message, Toast.LENGTH_SHORT).show();
}
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
final int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, BluetoothAdapter.ERROR);
if (state == BluetoothAdapter.STATE_ON) {
bluetoothOnOff.setText("Bluetooth is On");
blue2.setText("Bluetooth is On");
showEnabled();
final Handler handler5 = new Handler();
handler5.postDelayed(new Runnable() {
#Override
public void run() {
mediaplayer.start();
}
}, 500);
final Handler handler = new Handler();
handler.postDelayed(new Runnable() {
#Override
public void run() {
bluetoothOnOff.animate().translationY(150f).setDuration(5000);
blue2.animate().translationY(150f).setDuration(5000);
bluetoothOnOff.animate().alpha(0f).setDuration(3000);
blue2.animate().alpha(1f).setDuration(3000);
}
}, 500);
}
} else if (BluetoothAdapter.ACTION_DISCOVERY_STARTED.equals(action)) {
mDeviceList = new ArrayList<BluetoothDevice>();
mProgressDlg.show();
} else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
mProgressDlg.dismiss();
// Intent newIntent = new Intent(BluetoothConnectionActivity.this, DeviceList.class);
//
// newIntent.putParcelableArrayListExtra("device.list", mDeviceList);
//
// startActivity(newIntent);
} else if (BluetoothDevice.ACTION_FOUND.equals(action)) {
BluetoothDevice device = (BluetoothDevice) intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
mDeviceList.add(device);
Toast toast = Toast.makeText(getApplicationContext()," Found device" + device.getName(), Toast.LENGTH_SHORT);
View view3 = toast.getView();
view3.setBackgroundColor(Color.parseColor("#ffff5b"));
TextView text = (TextView) view3.findViewById(android.R.id.message);
text.setTextColor(Color.parseColor("#000000"));
toast.show();
}
}
};
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.optionmenu,menu);
return super.onCreateOptionsMenu(menu);
}
}
Device list Class :
public class DeviceList extends AppCompatActivity {
private ListView mListView;
private AdapterClassBluetooth mAdapterClassBluetooth;
private ArrayList<BluetoothDevice> mDeviceList;
private BluetoothDevice device ;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_device_list);
mDeviceList = getIntent().getExtras().getParcelableArrayList("device.list");
mListView = (ListView) findViewById(R.id.lv_paired);
mAdapterClassBluetooth = new AdapterClassBluetooth(this);
mAdapterClassBluetooth.setData(mDeviceList);
mAdapterClassBluetooth.setListener(new AdapterClassBluetooth.OnPairButtonClickListener() {
#Override
public void onPairButtonClick(int position) {
BluetoothDevice device = mDeviceList.get(position);
if (device.getBondState() == BluetoothDevice.BOND_BONDED) {
unpairDevice(device);
} else {
Toast toast = Toast.makeText(getApplicationContext(), "Pairing..." , Toast.LENGTH_SHORT);
View view = toast.getView();
view.setBackgroundColor(Color.parseColor("#ffff5b"));
TextView text = (TextView) view.findViewById(android.R.id.message);
text.setTextColor(Color.parseColor("#000000"));
toast.show();
pairDevice(device);
}
}
});
mListView.setAdapter(mAdapterClassBluetooth);
registerReceiver(mPairReceiver, new IntentFilter(BluetoothDevice.ACTION_BOND_STATE_CHANGED));
}
#Override
public void onDestroy() {
unregisterReceiver(mPairReceiver);
super.onDestroy();
}
private void showToast(String message) {
Toast.makeText(getApplicationContext(), message, Toast.LENGTH_SHORT).show();
}
private void pairDevice(BluetoothDevice device) {
try {
Method method = device.getClass().getMethod("createBond", (Class[]) null);
method.invoke(device, (Object[]) null);
} catch (Exception e) {
e.printStackTrace();
}
}
private void unpairDevice(BluetoothDevice device) {
try {
Method method = device.getClass().getMethod("removeBond", (Class[]) null);
method.invoke(device, (Object[]) null);
} catch (Exception e) {
e.printStackTrace();
}
}
private final BroadcastReceiver mPairReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (BluetoothDevice.ACTION_BOND_STATE_CHANGED.equals(action)) {
final int state = intent.getIntExtra(BluetoothDevice.EXTRA_BOND_STATE, BluetoothDevice.ERROR);
final int prevState = intent.getIntExtra(BluetoothDevice.EXTRA_PREVIOUS_BOND_STATE, BluetoothDevice.ERROR);
if (state == BluetoothDevice.BOND_BONDED && prevState == BluetoothDevice.BOND_BONDING) {
Toast toast = Toast.makeText(getApplicationContext()," Device are paired, please wait...", Toast.LENGTH_SHORT);
View view = toast.getView();
view.setBackgroundColor(Color.parseColor("#ffff5b"));
TextView text = (TextView) view.findViewById(android.R.id.message);
text.setTextColor(Color.parseColor("#000000"));
toast.show();
Handler delaying = new Handler();
delaying.postDelayed(new Runnable() {
#Override
public void run() {
Intent communicate = new Intent(DeviceList.this,Security.class);
startActivity(communicate);
finish();
}
},1500);
} else if (state == BluetoothDevice.BOND_NONE && prevState == BluetoothDevice.BOND_BONDED){
Toast toast = Toast.makeText(getApplicationContext(),"Unpaired.", Toast.LENGTH_SHORT);
View view = toast.getView();
view.setBackgroundColor(Color.parseColor("#ffff5b"));
TextView text = (TextView) view.findViewById(android.R.id.message);
text.setTextColor(Color.parseColor("#000000"));
toast.show();
}
mAdapterClassBluetooth.notifyDataSetChanged();
}
}
};}
Adapter class :
public class AdapterClassBluetooth extends BaseAdapter{
private LayoutInflater mInflater;
private List<BluetoothDevice> mData;
private OnPairButtonClickListener mListener;
public AdapterClassBluetooth(){
}
public AdapterClassBluetooth(Context context) {
super();
mInflater = LayoutInflater.from(context);
}
public void setData(List<BluetoothDevice> data) {
mData = data;
}
public void setListener(OnPairButtonClickListener listener) {
mListener = listener;
}
public int getCount() {
return (mData == null) ? 0 : mData.size();
}
public Object getItem(int position) {
return null;
}
public long getItemId(int position) {
return position;
}
public View getView(final int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.adapterlist, null);
holder = new ViewHolder();
holder.nameTv = (TextView) convertView.findViewById(R.id.tv_name);
holder.addressTv = (TextView) convertView.findViewById(R.id.tv_address);
holder.pairBtn = (Button) convertView.findViewById(R.id.btn_pair);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
BluetoothDevice device = mData.get(position);
holder.nameTv.setText(device.getName());
holder.addressTv.setText(device.getAddress());
holder.pairBtn.setText((device.getBondState() == BluetoothDevice.BOND_BONDED) ? "Unpair" : "Pair");
holder.pairBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (mListener != null) {
mListener.onPairButtonClick(position);
}
}
});
return convertView;
}
static class ViewHolder {
TextView nameTv;
TextView addressTv;
TextView pairBtn;
}
public interface OnPairButtonClickListener {
public abstract void onPairButtonClick(int position);
}
}
in an article i studied about this issue and find out that with this code :
if (ContextCompat.checkSelfPermission(context, Manifest.permission.ACCESS_COARSE_LOCATION)
!= PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(context,
new String[]{Manifest.permission.ACCESS_COARSE_LOCATION},
1);
i can make the application to support phones with android more than 6 so i can discover all nearby devices and pair with them,
The issue is, i don't know where should i exactly use this code..
i would really appreciate if you could tell me where to use it within the codes i showed here.
or simply tell me how to overcome this problem with any other code you may know.

In your AndroidManifest.xml file add this:
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
Then, instead of calling registerReceiver call this function:
private tryRegisterReceiver() {
if (ContextCompat.checkSelfPermission(thisActivity,
Manifest.permission.ACCESS_COARSE_LOCATION)
!= PackageManager.PERMISSION_GRANTED) {
// Here, permission is not granted
// after calling requestPermissions, the result must be treated in onRequestPermissionResult
ActivityCompat.requestPermissions(thisActivity,
new String[]{Manifest.permission.ACCESS_COARSE_LOCATION},
1000); // 100 or other desired code
} else {
// Permission has already been granted
// continue registering your receiver
registerReceiver();
}
}
To treat the result of the permission request
#Override
public void onRequestPermissionsResult(int requestCode,
String[] permissions, int[] grantResults) {
switch (requestCode) {
case 1000: {
// If request is cancelled, the result arrays are empty.
if (grantResults.length > 0
&& grantResults[0] == PackageManager.PERMISSION_GRANTED) {
// permission was granted
// continue registering your receiver
registerReceiver();
} else {
// permission denied
// show a message or finish your activity
}
return;
}
// other 'case' for other permissions if needed
}
}

App crashes after clicking scan button for the first time but the app works after i reopen it

I'm trying to create an indoor location services app in android studio.There is a scan button which start the discovery of BLE devices. When i click on the scan button,the app crashes. But when i reopen the app and click on the scan button again,it works.
i tried this taken from one of the projects from stackoverflow.
Class variable:
private BluetoothAdapter mBtAdapter = null;
final BluetoothManager btManager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
mBtAdapter = btManager.getAdapter();
if (mBtAdapter == null || !mBtAdapter.isEnabled()) {
Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}
}
public void onScanButton(){
if (mBtAdapter.isEnabled()){
scanLeDevice(true);
}
}
this is my code
BluetoothManager btManager; //field 'btManager' is never used
private BluetoothAdapter btAdapter = null;
BluetoothLeScanner btScanner;
Button startScanningButton;
Button stopScanningButton;
TextView peripheralTextView;
private final static int REQUEST_ENABLE_BT = 1;
private static final int PERMISSION_REQUEST_COARSE_LOCATION = 1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
peripheralTextView = (TextView) findViewById(R.id.peripheralTextView);
peripheralTextView.setMovementMethod(new ScrollingMovementMethod());
startScanningButton = (Button) findViewById(R.id.StartScanButton);
startScanningButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
startScanning();
}
});
stopScanningButton = (Button) findViewById(R.id.StopScanButton);
stopScanningButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
stopScanning();
}
});
stopScanningButton.setVisibility(View.INVISIBLE);
final BluetoothManager btManager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
btAdapter = btManager.getAdapter();
btScanner = btAdapter.getBluetoothLeScanner();
if (btAdapter != null && !btAdapter.isEnabled()) {
Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableIntent,REQUEST_ENABLE_BT);
}
// Make sure we have access coarse location enabled, if not, prompt the user to enable it
if (this.checkSelfPermission(Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
final AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("This app needs location access");
builder.setMessage("Please grant location access so this app can detect peripherals.");
builder.setPositiveButton(android.R.string.ok, null);
builder.setOnDismissListener(new DialogInterface.OnDismissListener() {
#Override
public void onDismiss(DialogInterface dialog) {
requestPermissions(new String[]{Manifest.permission.ACCESS_COARSE_LOCATION}, PERMISSION_REQUEST_COARSE_LOCATION);
}
});
builder.show();
}
}
// Device scan callback.
private ScanCallback leScanCallback = new ScanCallback() {
#Override
public void onScanResult(int callbackType, ScanResult result) {
peripheralTextView.append("MAC address: " + result.getDevice().getAddress() + " rssi: " + result.getRssi() + "TxPower:" + result.getTxPower() + "\n");
// auto scroll for text view
final int scrollAmount = peripheralTextView.getLayout().getLineTop(peripheralTextView.getLineCount()) - peripheralTextView.getHeight();
// if there is no need to scroll, scrollAmount will be <=0
if (scrollAmount > 0)
peripheralTextView.scrollTo(0, scrollAmount);
}
};
#Override
public void onRequestPermissionsResult(int requestCode,
String permissions[], int[] grantResults) {
switch (requestCode) {
case PERMISSION_REQUEST_COARSE_LOCATION: {
if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
System.out.println("coarse location permission granted");
} else {
final AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Functionality limited");
builder.setMessage("Since location access has not been granted, this app will not be able to discover beacons when in the background.");
builder.setPositiveButton(android.R.string.ok, null);
builder.setOnDismissListener(new DialogInterface.OnDismissListener() {
#Override
public void onDismiss(DialogInterface dialog) {
}
});
builder.show();
}
}
}
}
public void startScanning() {
System.out.println("start scanning");
peripheralTextView.setText("");
startScanningButton.setVisibility(View.INVISIBLE);
stopScanningButton.setVisibility(View.VISIBLE);
AsyncTask.execute(new Runnable() {
#Override
public void run() {
btScanner.startScan(leScanCallback);
}
});
}
public void stopScanning() {
System.out.println("stopping scanning");
peripheralTextView.append("Stopped Scanning");
startScanningButton.setVisibility(View.VISIBLE);
stopScanningButton.setVisibility(View.INVISIBLE);
AsyncTask.execute(new Runnable() {
#Override
public void run() {
btScanner.stopScan(leScanCallback);
}
});
}
}
The logcat shows
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.bluetooth.le.BluetoothLeScanner.startScan(android.bluetooth.le.ScanCallback)' on a null object reference
at com.example.myapplication.MainActivity$6.run(MainActivity.java:137)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
at java.lang.Thread.run(Thread.java:764)

Before i click the Scan button,a prompt will be display asking to turn
on the bluetooth.So bluetooth will be turned on
You are wrong about that part. You ask the user to enable it, but it might not have happened yet. At least you need to get the Scanner later on.
Currently you set the Scanner reference before the permission requesting has been initiated.
This also explains why it works after your App has crashed for the first time, because the 2nd time you come here the Permission has been enabled.
From the Javadoc of BluetoothAdapter#getBluetoothLeScanner():
Will return null if Bluetooth is turned off or if Bluetooth LE
Advertising is not supported on this device.
You can change your code to:
public void startScanning() {
btScanner = btAdapter.getBluetoothLeScanner();
if (btScanner == null) {
// not enabled yet or not supported
return;
}
System.out.println("start scanning");
peripheralTextView.setText("");
startScanningButton.setVisibility(View.INVISIBLE);
stopScanningButton.setVisibility(View.VISIBLE);
AsyncTask.execute(new Runnable() {
#Override
public void run() {
btScanner.startScan(leScanCallback);
}
});
}

Android studio app crashes while attempting to send file over bluetooth

Android bluetooth app crashes while trying to send data via bluetooth. I was able to turn on, make discoverable, and show paired devices. But, it crashes when i attempt the send file button. Im getting these errors in my Debugger.
Process: com.example.bluetooth_demoproject, PID: 31320
java.lang.NullPointerException: Attempt to get length of null
array
at com.example.bluetooth_demoproject.MainActivity.ListDir(MainActivity.java:253)
at com.example.bluetooth_demoproject.MainActivity.onPrepareDialog(MainActivity.java:228)
at android.app.Activity.onPrepareDialog(Activity.java:4000)
at android.app.Activity.showDialog(Activity.java:4063)
at android.app.Activity.showDialog(Activity.java:4014)
at
com.example.bluetooth_demoproject.MainActivity$1.onClick(MainActivity.java:75)
at android.view.View.performClick(View.java:6896)
at
android.widget.TextView.performClick(TextView.java:12689)
at android.view.View$PerformClick.run(View.java:26088)
at android.os.Handler.handleCallback(Handler.java:789)
at android.os.Handler.dispatchMessage(Handler.java:98)
at android.os.Looper.loop(Looper.java:164)
at
android.app.ActivityThread.main(ActivityThread.java:6940)
at java.lang.reflect.Method.invoke(Native Method)
at
com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)
Also here is my MainActivity. If theres a better way to sending files via
bluetooth please point it out or help with my code.
public class MainActivity extends Activity {
// Creating objects -----------------------------
private static final int REQUEST_ENABLE_BT = 0;
private static final int REQUEST_DISCOVER_BT_ = 1;
private static int CUSTOM_DIALOG_ID;
ListView dialog_ListView;
TextView mBluetoothStatus, mPairedDevicesList, mTextFolder;
ImageView mBluetoothIcon;
Button mOnButton, mOffButton, mDiscoverableButton, mPairedDevices,
mbuttonOpenDialog, msendBluetooth, mbuttonUp;
File root, fileroot, curFolder;
EditText dataPath;
private static final int DISCOVER_DURATION = 300;
private List<String> fileList = new ArrayList<String>();
// -------------------------------------------------------
BluetoothAdapter mBlueAdapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dataPath =(EditText) findViewById(R.id.FilePath);
mTextFolder = findViewById(R.id.folder);
mBluetoothStatus = findViewById(R.id.BluetoothStatus);
mBluetoothIcon = findViewById(R.id.bluetoothIcon);
mOnButton = findViewById(R.id.onButton);
mOffButton = findViewById(R.id.offButton);
mDiscoverableButton = findViewById(R.id.discoverableButton);
mPairedDevices = findViewById(R.id.pairedDevices);
mPairedDevicesList = findViewById(R.id.pairedDeviceList);
mbuttonOpenDialog = findViewById(R.id.opendailog);
msendBluetooth = findViewById(R.id.sendBluetooth);
mbuttonUp = findViewById(R.id.up);
mbuttonOpenDialog.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
dataPath.setText("");
showDialog(CUSTOM_DIALOG_ID);
}
});
root = new
File(Environment.getExternalStorageDirectory().getAbsolutePath());
curFolder = root;
msendBluetooth.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
sendViaBluetooth();
}
});
//adapter
mBlueAdapter = BluetoothAdapter.getDefaultAdapter();
if(mBlueAdapter == null){
mBluetoothStatus.setText("Bluetooth is not available");
return;
}
else {
mBluetoothStatus.setText("Bluetooth is available");
}
//if Bluetooth isnt enabled, enable it
if (!mBlueAdapter.isEnabled()) {
Intent enableBtIntent = new
Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}
//set image according to bluetooth Status
if (mBlueAdapter.isEnabled()) {
mBluetoothIcon.setImageResource(R.drawable.action_on);
}
else {
mBluetoothIcon.setImageResource(R.drawable.action_off);
}
//on button Click
mOnButton.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
if (!mBlueAdapter.isEnabled()) {
showToast("Turning Bluetooth on...");
// intent to on bluetooth
Intent intent = new
Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(intent, REQUEST_ENABLE_BT);
}
else {
showToast("Bluetooth is already on");
}
}
});
//discover Bluetooth button
mDiscoverableButton.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v){
if (!mBlueAdapter.isDiscovering()) {
showToast("Making device discoverable");
Intent intent = new
Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
startActivityForResult(intent, REQUEST_DISCOVER_BT_);
}
}
});
// off button click
mOffButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (mBlueAdapter.isEnabled()) {
showToast("Turning Bluetooth off...");
// intent to turn off bluetooth
mBluetoothIcon.setImageResource(R.drawable.action_off);
}
else{
showToast("Bluetooth is already off");
}
}
});
//get paired device button click
mPairedDevices.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (mBlueAdapter.isEnabled()) {
mPairedDevices.setText("Paired Devices");
Set<BluetoothDevice> devices =
mBlueAdapter.getBondedDevices();
for (BluetoothDevice device : devices){
mPairedDevices.append("\nDevice: " + device.getName() +
"," + device );
}
}
else {
//bluetooth is off and cant get paired devices
showToast("Turn on bluetooth to get paired devices");
}
}
});
}
#Override
protected Dialog onCreateDialog(int id) {
Dialog dialog = null;
if (id == CUSTOM_DIALOG_ID) {
dialog = new Dialog(MainActivity.this);
dialog.setContentView(R.layout.dailoglayout);
dialog.setTitle("File Selector");
dialog.setCancelable(true);
dialog.setCanceledOnTouchOutside(true);
mTextFolder = (TextView) dialog.findViewById(R.id.folder);
mbuttonUp = (Button) dialog.findViewById(R.id.up);
mbuttonUp.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
ListDir(curFolder.getParentFile());
}
});
dialog_ListView = (ListView) dialog.findViewById(R.id.dialoglist);
dialog_ListView.setOnItemClickListener(new
AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int
position, long id) {
File selected = new File(fileList.get(position));
if (selected.isDirectory()) {
ListDir(selected);
} else if (selected.isFile()) {
getSelectedFile(selected);
} else {
dismissDialog(CUSTOM_DIALOG_ID);
}
}
});
}
return dialog;
}
#Override
protected void onPrepareDialog(int id, Dialog dialog) {
super.onPrepareDialog(id, dialog);
if (id == CUSTOM_DIALOG_ID) {
ListDir(curFolder);
}
}
public void getSelectedFile(File f) {
dataPath.setText(f.getAbsolutePath());
fileList.clear();
dismissDialog(CUSTOM_DIALOG_ID);
}
public void ListDir(File f) {
if (f.equals(root)) {
mbuttonUp.setEnabled(false);
}
else {
mbuttonUp.setEnabled(true);
}
curFolder = f;
mTextFolder.setText(f.getAbsolutePath());
dataPath.setText(f.getAbsolutePath());
File[] files = f.listFiles();
fileList.clear();
for (File file : files) {
fileList.add(file.getPath());
}
ArrayAdapter<String> directoryList = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, fileList);
dialog_ListView.setAdapter(directoryList);
}
// exits to app --------------------------------
public void exit(View V) {
mBlueAdapter.disable();
Toast.makeText(this, "*** Now bluetooth is off...",
Toast.LENGTH_LONG).show();
finish();
}
// send file via bluetooth ------------------------
public void sendViaBluetooth() {
if(!dataPath.equals(null)) {
if(mBlueAdapter == null) {
Toast.makeText(this, "Device doesnt support bluetooth",
Toast.LENGTH_LONG).show();
}
else {
enableBluetooth();
}
}
else {
Toast.makeText(this, "please select a file",
Toast.LENGTH_LONG).show();
}
}
public void enableBluetooth() {
showToast("Making device discoverable");
Intent intent = new
Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
startActivityForResult(intent, REQUEST_DISCOVER_BT_);
}
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent
data) {
if (resultCode == DISCOVER_DURATION && requestCode ==
REQUEST_DISCOVER_BT_) {
Intent i = new Intent();
i.setAction(Intent.ACTION_SEND);
i.setType("*/*");
File file = new File(dataPath.getText().toString());
i.putExtra(Intent.EXTRA_STREAM, Uri.fromFile(file));
PackageManager pm = getPackageManager();
List<ResolveInfo> list = pm.queryIntentActivities(i, 0);
if (list.size() > 0) {
String packageName = null;
String className = null;
boolean found = false;
for (ResolveInfo info : list) {
packageName = info.activityInfo.packageName;
if (packageName.equals("com.android.bluetooth")) {
className = info.activityInfo.name;
found = true;
}
}
//CHECK BLUETOOTH available or not------------------------------
------------------
if (!found) {
Toast.makeText(this, "Bluetooth not been found",
Toast.LENGTH_LONG).show();
} else {
i.setClassName(packageName, className);
startActivity(i);
}
}
} else {
Toast.makeText(this, "Bluetooth is cancelled",
Toast.LENGTH_LONG).show();
}
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
return super.onOptionsItemSelected(item);
}
//toast message function
private void showToast(String msg) {
Toast.makeText(this, msg, Toast.LENGTH_SHORT) .show();
}
}

Unable to send characters to Arduino through Android App

I have succeeded in sending characters from a bletooth terminal App to Arduino and it worked.
Now, I am trying to send some characters to my arduino using my own app and I have programmed the HC05 Bluetooth module in slave mode so that it can only receive data. I used this code Reference code for bluetooth chat as a starting point so that later I can modify it according to my needs to only transfer characters from android to arduino.
But As soon as I hit send button after typing a character on my phone I get the following error in my logcat:
05-05 16:06:41.966 8042-8042/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.android.bluetoothtest, PID: 8042
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.android.bluetoothtest.BluetoothConnectionService.write(byte[])' on a null object reference
at com.example.android.bluetoothtest.MainActivity$7.onClick(MainActivity.java:227)
at android.view.View.performClick(View.java:5640)
at android.view.View$PerformClick.run(View.java:22455)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6165)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)
Java File:
MainActivity.java
public class MainActivity extends AppCompatActivity implements
AdapterView.OnItemClickListener{
private static final String TAG = "MainActivity";
BluetoothAdapter mBluetoothAdapter;
Button btnEnableDisable_Discoverable;
BluetoothConnectionService mBluetoothConnection;
Button btnStartConnection;
Button btnSend;
EditText etSend;
private static final UUID MY_UUID_INSECURE =
UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
BluetoothDevice mBTDevice;
public ArrayList<BluetoothDevice> mBTDevices = new ArrayList<>();
public DeviceListAdapter mDeviceListAdapter;
ListView lvNewDevices;
// Create a BroadcastReceiver for ACTION_FOUND
private final BroadcastReceiver mBroadcastReceiver1 = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
// When discovery finds a device
if (action.equals(mBluetoothAdapter.ACTION_STATE_CHANGED)) {
final int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, mBluetoothAdapter.ERROR);
switch(state){
case BluetoothAdapter.STATE_OFF:
Log.d(TAG, "onReceive: STATE OFF");
break;
case BluetoothAdapter.STATE_TURNING_OFF:
Log.d(TAG, "mBroadcastReceiver1: STATE TURNING OFF");
break;
case BluetoothAdapter.STATE_ON:
Log.d(TAG, "mBroadcastReceiver1: STATE ON");
break;
case BluetoothAdapter.STATE_TURNING_ON:
Log.d(TAG, "mBroadcastReceiver1: STATE TURNING ON");
break;
}
}
}
};
/**
* Broadcast Receiver for changes made to bluetooth states such as:
* 1) Discoverability mode on/off or expire.
*/
private final BroadcastReceiver mBroadcastReceiver2 = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if (action.equals(BluetoothAdapter.ACTION_SCAN_MODE_CHANGED)) {
int mode = intent.getIntExtra(BluetoothAdapter.EXTRA_SCAN_MODE, BluetoothAdapter.ERROR);
switch (mode) {
//Device is in Discoverable Mode
case BluetoothAdapter.SCAN_MODE_CONNECTABLE_DISCOVERABLE:
Log.d(TAG, "mBroadcastReceiver2: Discoverability Enabled.");
break;
//Device not in discoverable mode
case BluetoothAdapter.SCAN_MODE_CONNECTABLE:
Log.d(TAG, "mBroadcastReceiver2: Discoverability Disabled. Able to receive connections.");
break;
case BluetoothAdapter.SCAN_MODE_NONE:
Log.d(TAG, "mBroadcastReceiver2: Discoverability Disabled. Not able to receive connections.");
break;
case BluetoothAdapter.STATE_CONNECTING:
Log.d(TAG, "mBroadcastReceiver2: Connecting....");
break;
case BluetoothAdapter.STATE_CONNECTED:
Log.d(TAG, "mBroadcastReceiver2: Connected.");
break;
}
}
}
};
/**
* Broadcast Receiver for listing devices that are not yet paired
* -Executed by btnDiscover() method.
*/
private BroadcastReceiver mBroadcastReceiver3 = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
Log.d(TAG, "onReceive: ACTION FOUND.");
if (action.equals(BluetoothDevice.ACTION_FOUND)){
BluetoothDevice device = intent.getParcelableExtra (BluetoothDevice.EXTRA_DEVICE);
mBTDevices.add(device);
Log.d(TAG, "onReceive: " + device.getName() + ": " + device.getAddress());
mDeviceListAdapter = new DeviceListAdapter(context, R.layout.device_adapter_view, mBTDevices);
lvNewDevices.setAdapter(mDeviceListAdapter);
}
}
};
/**
* Broadcast Receiver that detects bond state changes (Pairing status changes)
*/
private final BroadcastReceiver mBroadcastReceiver4 = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if(action.equals(BluetoothDevice.ACTION_BOND_STATE_CHANGED)){
BluetoothDevice mDevice = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
//3 cases:
//case1: bonded already
if (mDevice.getBondState() == BluetoothDevice.BOND_BONDED){
Log.d(TAG, "BroadcastReceiver: BOND_BONDED.");
//inside BroadcastReceiver4
mBTDevice = mDevice;
}
//case2: creating a bone
if (mDevice.getBondState() == BluetoothDevice.BOND_BONDING) {
Log.d(TAG, "BroadcastReceiver: BOND_BONDING.");
}
//case3: breaking a bond
if (mDevice.getBondState() == BluetoothDevice.BOND_NONE) {
Log.d(TAG, "BroadcastReceiver: BOND_NONE.");
}
}
}
};
#Override
protected void onDestroy() {
Log.d(TAG, "onDestroy: called.");
super.onDestroy();
unregisterReceiver(mBroadcastReceiver1);
unregisterReceiver(mBroadcastReceiver2);
unregisterReceiver(mBroadcastReceiver3);
unregisterReceiver(mBroadcastReceiver4);
//mBluetoothAdapter.cancelDiscovery();
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button btnONOFF = (Button) findViewById(R.id.btnONOFF);
btnEnableDisable_Discoverable = (Button) findViewById(R.id.btnDiscoverable_on_off);
lvNewDevices = (ListView) findViewById(R.id.lvNewDevices);
mBTDevices = new ArrayList<>();
btnStartConnection = (Button) findViewById(R.id.btnStartConnection);
btnSend = (Button) findViewById(R.id.btnSend);
etSend = (EditText) findViewById(R.id.editText);
//Broadcasts when bond state changes (ie:pairing)
IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_BOND_STATE_CHANGED);
registerReceiver(mBroadcastReceiver4, filter);
mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
lvNewDevices.setOnItemClickListener(MainActivity.this);
btnONOFF.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Log.d(TAG, "onClick: enabling/disabling bluetooth.");
enableDisableBT();
}
});
btnStartConnection.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
startConnection();
}
});
btnSend.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
byte[] bytes = etSend.getText().toString().getBytes(Charset.defaultCharset());
mBluetoothConnection.write(bytes);
}
});
}
//create method for starting connection
//***remember the conncction will fail and app will crash if you haven't
paired first
public void startConnection(){
startBTConnection(mBTDevice,MY_UUID_INSECURE);
}
/**
* starting chat service method
*/
public void startBTConnection(BluetoothDevice device, UUID uuid){
Log.d(TAG, "startBTConnection: Initializing RFCOM Bluetooth Connection.");
mBluetoothConnection.startClient(device,uuid);
}
public void enableDisableBT(){
if(mBluetoothAdapter == null){
Log.d(TAG, "enableDisableBT: Does not have BT capabilities.");
}
if(!mBluetoothAdapter.isEnabled()){
Log.d(TAG, "enableDisableBT: enabling BT.");
Intent enableBTIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivity(enableBTIntent);
IntentFilter BTIntent = new IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED);
registerReceiver(mBroadcastReceiver1, BTIntent);
}
if(mBluetoothAdapter.isEnabled()){
Log.d(TAG, "enableDisableBT: disabling BT.");
mBluetoothAdapter.disable();
IntentFilter BTIntent = new IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED);
registerReceiver(mBroadcastReceiver1, BTIntent);
}
}
public void btnEnableDisable_Discoverable(View view) {
Log.d(TAG, "btnEnableDisable_Discoverable: Making device discoverable for 300 seconds.");
Intent discoverableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300);
startActivity(discoverableIntent);
IntentFilter intentFilter = new IntentFilter(mBluetoothAdapter.ACTION_SCAN_MODE_CHANGED);
registerReceiver(mBroadcastReceiver2,intentFilter);
}
public void btnDiscover(View view) {
Log.d(TAG, "btnDiscover: Looking for unpaired devices.");
if(mBluetoothAdapter.isDiscovering()){
mBluetoothAdapter.cancelDiscovery();
Log.d(TAG, "btnDiscover: Canceling discovery.");
//check BT permissions in manifest
checkBTPermissions();
mBluetoothAdapter.startDiscovery();
IntentFilter discoverDevicesIntent = new IntentFilter(BluetoothDevice.ACTION_FOUND);
registerReceiver(mBroadcastReceiver3, discoverDevicesIntent);
}
if(!mBluetoothAdapter.isDiscovering()){
//check BT permissions in manifest
checkBTPermissions();
mBluetoothAdapter.startDiscovery();
IntentFilter discoverDevicesIntent = new IntentFilter(BluetoothDevice.ACTION_FOUND);
registerReceiver(mBroadcastReceiver3, discoverDevicesIntent);
}
}
/**
* This method is required for all devices running API23+
* Android must programmatically check the permissions for bluetooth. Putting the proper permissions
* in the manifest is not enough.
*
* NOTE: This will only execute on versions > LOLLIPOP because it is not needed otherwise.
*/
private void checkBTPermissions() {
if(Build.VERSION.SDK_INT > Build.VERSION_CODES.LOLLIPOP){
int permissionCheck = this.checkSelfPermission("Manifest.permission.ACCESS_FINE_LOCATION");
permissionCheck += this.checkSelfPermission("Manifest.permission.ACCESS_COARSE_LOCATION");
if (permissionCheck != 0) {
this.requestPermissions(new String[]{Manifest.permission.ACCESS_FINE_LOCATION, Manifest.permission.ACCESS_COARSE_LOCATION}, 1001); //Any number
}
}else{
Log.d(TAG, "checkBTPermissions: No need to check permissions. SDK version < LOLLIPOP.");
}
}
#Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
//first cancel discovery because its very memory intensive.
mBluetoothAdapter.cancelDiscovery();
Log.d(TAG, "onItemClick: You Clicked on a device.");
String deviceName = mBTDevices.get(i).getName();
String deviceAddress = mBTDevices.get(i).getAddress();
Log.d(TAG, "onItemClick: deviceName = " + deviceName);
Log.d(TAG, "onItemClick: deviceAddress = " + deviceAddress);
//create the bond.
//NOTE: Requires API 17+? I think this is JellyBean
if(Build.VERSION.SDK_INT > Build.VERSION_CODES.JELLY_BEAN_MR2){
Log.d(TAG, "Trying to pair with " + deviceName);
mBTDevices.get(i).createBond();
mBTDevice = mBTDevices.get(i);
mBluetoothConnection = new BluetoothConnectionService(MainActivity.this);
}
}
}
Please help me, I can't seem to find a solution at all, I am a novice.
Thank You, Any help is greatly appreciated.

You MUST initialize BluetoothConnectionService before send anything to the Bluetooth
call this line before sending any data
....
mBluetoothConnection = new BluetoothConnectionService(MainActivity.this);
startConnection();
mBluetoothConnection.write(bytes);
and make sure that bytes are not null, try to print it in LOG

Java Android bluetooth connection and add result of searching devices in a listview

I'm trying to make a java android application with bluetooth and I have some troubles to show the result after search all the devices paired or not in a listview and to connect to a device, in my code I'm trying to connect with a device using the mac addres of it, but it doesn't work and I show the result in a textview, any idea????
Thank you.
public class Conexion_bluetooth extends Activity {
TextView out;
// Debugging
private static final UUID MY_UUID = UUID.fromString("fa87c0d0-afac-11de-8a39-0800200c9a66");
private BluetoothAdapter mBluetoothAdapter = null;
private BluetoothSocket mmSocket=null;
private static final String TAG = "BluetoothChat";
private static final boolean D = true;
private static final int REQUEST_ENABLE_BT = 3;
private BluetoothAdapter mBluetoothAdapter = null;
ListView lstDispositivos;
ListView lstDispositivos2;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(D) Log.e(TAG, "+++ ON CREATE +++");
// Set up the window layout
setContentView(R.layout.activity_conexion_bluetooth);
// Get local Bluetooth adapter
mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
// If the adapter is null, then Bluetooth is not supported
if (mBluetoothAdapter == null) {
Toast.makeText(this, "Bluetooth is not available", Toast.LENGTH_LONG).show();
finish();
return;
}
}
#Override
//Comprueba que el bluetooth esta conectado
public void onStart() {
super.onStart();
if(D) Log.e(TAG, "++ ON START ++");
// Si el bluetooth no está activado muestra un mensaje solicitando permiso para activarle
if (!mBluetoothAdapter.isEnabled()) {
Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableIntent, REQUEST_ENABLE_BT);
Toast.makeText(this, "conectando...", Toast.LENGTH_LONG).show();
}else{
Toast.makeText(this, "conectado", Toast.LENGTH_LONG).show();
}
}
public void buscar(View view){
//TextView dispositivos = (TextView) findViewById(R.id.dispositivos);
if (mBluetoothAdapter.isDiscovering()) {
Toast.makeText(this, "\nCancel discovery...", Toast.LENGTH_LONG).show();
mBluetoothAdapter.cancelDiscovery();
}else{
Toast.makeText(this, "\nStarting discovery...", Toast.LENGTH_LONG).show();
//mBluetoothAdapter.
mBluetoothAdapter.startDiscovery();
Toast.makeText(this, "\nDone with discovery...", Toast.LENGTH_LONG).show();
}
final TextView dispositivos = (TextView) findViewById(R.id.dispositivos);
String dispositivo[] = new String[]{};
final Vector<String> dispositivosBT = new Vector<String>();
//final int dispEncontrados=0;
// Create a BroadcastReceiver for ACTION_FOUND
final BroadcastReceiver mReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
//String dispositivosBT[] = new String[]{};
String action = intent.getAction();
// When discovery finds a device
if (BluetoothDevice.ACTION_FOUND.equals(action)) {
//setContentView(R.layout.dispositivos_bluetooth);//determinamos que al iniciar la aplicacion aparezca esta pantalla
// Get the BluetoothDevice object from the Intent
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
// Add the name and address to an array adapter to show in a ListView
dispositivos.append("\n" + device.getName() + "\n" + device.getAddress());
}
}
};
// Register the BroadcastReceiver
IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
registerReceiver(mReceiver, filter); // Don't forget to unregister during onDestroy
//dispositivosBT = new String[dispositivos.length()];
//final ArrayAdapter<String> adaptador = new ArrayAdapter<String>(this, android.R.layout.simple_expandable_list_item_1, dispositivosBT);
final TextView dispositivosSincronizados = (TextView) findViewById(R.id.dispositivosSincronizados);
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
dispositivosSincronizados.append("\n" + device.getName() + "\n" + device.getAddress());
}
}
}
public void paraBusqueda(View view){
if (mBluetoothAdapter.isDiscovering()) {
Toast.makeText(this, "\nCancel discovery...", Toast.LENGTH_LONG).show();
mBluetoothAdapter.cancelDiscovery();
}else{
Toast.makeText(this, "\nis not discovering...", Toast.LENGTH_LONG).show();
}
}
public void pararBluetooth(){
if (mBluetoothAdapter.isEnabled()) {
Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableIntent, REQUEST_ENABLE_BT);
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_conexion_bluetooth, menu);
return true;
}
public void conectar(View view){
String address = "00:15:83:07:d1:14";
device = mBluetoothAdapter.getRemoteDevice(address);
Toast.makeText(getApplicationContext(), "cONNECTING", Toast.LENGTH_SHORT).show();
try {
mmSocket = device.createRfcommSocketToServiceRecord(MY_UUID);
mmSocket.connect();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

Using AsyncTask we can make Bluetooth Connection.
public class BluetoothConnectionActivity extends Activity {
private Button connectButton;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
connectButton = (Button) findViewById(R.id.connectButton);
connectButton.setOnclickListener(View.onClickListener() {
#Override
public void onClick(View v) {
String address = "00:15:83:07:d1:14";
new ConnectAsyncTask(address).execute();
}
});
}
private class ConnectAsyncTask extends AsyncTask<String, Void, Boolean> {
#Override
protected void onPostExecute(Boolean isConnected) {
Toast.makeText(getApplicationContext(), "Connecting...",
Toast.LENGTH_SHORT).show();
}
#Override
protected Boolean doInBackground(String... param) {
BluetoothDevice device = BluetoothAdapter
.getDefaultBluetoothAdapter().getRemoteDevice(param[0]);
try {
BluetoothSocket mmSocket = device
.createRfcommSocketToServiceRecord(MY_UUID);
mmSocket.connect();
} catch (Exception e) {
e.printStackTrace();
Log.d("BluetoothConnectivity", "ERROR:" + e.getMessage());
return false;
}
return true;
}
#Override
protected void onPostExecute(Boolean isConnected) {
if (isConnected) {
Toast.makeText(getApplicationContext(), "Connected",
Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(getApplicationContext(), "Failed to connected",
Toast.LENGTH_SHORT).show();
}
}
}
}
Regards
Srini

Recently we played with bluetooth for some application. i am not an expert in android. You can try the following things.
1. check your bluetooth device's UUID
2. Connecting to Bluetooth need to be in a separate thread
3. Run app in debug mode and check the Exception or error.
Refer the android bluetooth documentation
If you still have the same problem look at Bluetooth sample application, otherwise i will send the code which i had written for making connection.
regards
srini