BluetoothLeScanner null object reference

Question

I have a problem regarding my Bluetooth app. When I enable Bluetooth before starting up the app everything works alright. But when I don't, my app will ask permission to enable Bluetooth via the turnOn method. But when I press my onScan button I get a error stating:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.bluetooth.le.BluetoothLeScanner.startScan(android.bluetooth.le.ScanCallback)' on a null object reference

here is my onCreate method:

 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //Set layout
    setContentView(R.layout.activity_main);
    //Bluetooth
    // BluetoothManager
    final BluetoothManager BTManager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
    BTAdapter = BTManager.getAdapter();
    // BluetoothLescanner
    BTScanner = BTAdapter.getBluetoothLeScanner();
    //Turn on BT
    turnOn();
    //Ask permission for location.
    requestPermission();
}

My ques is that, BTScanner is made before the turnOn method is called, making the BTScanner a null object.

Any help regarding this problem would be greatly.

Kind regards,

Binsento

Answer 1

Try this (taken from one of my projects):

Class variable:

private BluetoothAdapter mBtAdapter = null;

Inside onCreate:

final BluetoothManager btManager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
    mBtAdapter = btManager.getAdapter();

checkBt(); // called at the end of onCreate

The checkBt() method:

private void checkBt() {
    if (mBtAdapter == null || !mBtAdapter.isEnabled()) {
        Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
    }
}

Then from there when the "Scan" button is clicked:

public void onScanButton(){
    if (mBtAdapter.isEnabled()){
        scanLeDevice(true);
    }
}

Then scanLeDevice calls mBtAdapter.startLeScan(mLeScanCallback);

NOTE: Some of this is now deprecated but can be updated to comply with the new API. I have not taken the time to do that.