Android Bluetooth Low Energy code compatible with API>=21 AND API<21

Question

I'm developing an app that have to connect with a BLE device, in my code I want to use the new Scan and ScanCallback for BLE implemented from API 21 (Android 5) but I have to maintain the compatibility with Android 4.3 and above.

So I wrote the code, for example, in this way:

        if (Build.VERSION.SDK_INT >= 21) {
            mLEScanner.startScan(filters, settings, mScanCallback);
        } else {
            btAdapter.startLeScan(leScanCallback);
        }

And I have defined the 2 callbacks, one for API 21 and above and one for API 18 to 20:

    //API 21
private ScanCallback mScanCallback = new ScanCallback() {
        @Override
        public void onScanResult(int callbackType, ScanResult result) {
              BluetoothDevice btDevice = result.getDevice();
              connectToDevice(btDevice);
         }
         public void connectToDevice(BluetoothDevice device) {
              if (mGatt == null) {
                   mGatt = device.connectGatt(context, false, btleGattCallback);
                   if (Build.VERSION.SDK_INT < 21) {
                        btAdapter.stopLeScan(leScanCallback);
                   } else {
                        mLEScanner.stopScan(mScanCallback);
                   }
               }
         }
    };


//API 18 to 20
        private BluetoothAdapter.LeScanCallback leScanCallback = new BluetoothAdapter.LeScanCallback() {
        @Override
        public void onLeScan(final BluetoothDevice device, final int rssi, final byte[] scanRecord) {

        btAdapter.stopLeScan(leScanCallback);
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                mBluetoothGatt = device.connectGatt(context, false, btleGattCallback);
            }
        });


    }
};

I also added the annotation

@TargetApi(21)

but when I launch the App on Android 4.x it crashes immediately reporting the error that the class ScanCallback cannot be found (the one intended to be used only with Android 5 and above).

How can I solve this?

Thank you very much. Daniele.

Answer 1

After reading several posts I did the following. Just in case, here is the documentation of Android about BluetoothLe

First

Create two methods one scanLeDevice21 and scanLeDevice18. On scanLeDevice21 add the annotation @RequiresApi(21) that says:

Denotes that the annotated element should only be called on the given API level or higher. This is similar in purpose to the older @TargetApi annotation, but more clearly expresses that this is a requirement on the caller, rather than being used to "suppress" warnings within the method that exceed the minSdkVersion.

Second

Implement each method, here's my code.

@RequiresApi(21)
private void scanLeDevice21(final boolean enable) {

    ScanCallback mLeScanCallback = new ScanCallback() {

        @Override
        public void onScanResult(int callbackType, ScanResult result) {

            super.onScanResult(callbackType, result);

            BluetoothDevice bluetoothDevice = result.getDevice();

            if (!bluetoothDeviceList.contains(bluetoothDevice)) {
                Log.d("DEVICE", bluetoothDevice.getName() + "[" + bluetoothDevice.getAddress() + "]");
                bluetoothDeviceArrayAdapter.add(bluetoothDevice);
                bluetoothDeviceArrayAdapter.notifyDataSetChanged();
            }
        }

        @Override
        public void onBatchScanResults(List<ScanResult> results) {
            super.onBatchScanResults(results);

        }

        @Override
        public void onScanFailed(int errorCode) {
            super.onScanFailed(errorCode);
        }
    };

    final BluetoothLeScanner bluetoothLeScanner = mBluetoothAdapter.getBluetoothLeScanner();

    if (enable) {
        // Stops scanning after a pre-defined scan period.
        mHandler.postDelayed(() -> {
            mScanning = false;
            swipeRefreshLayout.setRefreshing(false);
            bluetoothLeScanner.stopScan(mLeScanCallback);
        }, SCAN_PERIOD);

        mScanning = true;
        bluetoothLeScanner.startScan(mLeScanCallback);
    } else {
        mScanning = false;
        bluetoothLeScanner.stopScan(mLeScanCallback);
    }
}


 /**
 * Scan BLE devices on Android API 18 to 20
 *
 * @param enable Enable scan
 */
private void scanLeDevice18(boolean enable) {

    BluetoothAdapter.LeScanCallback mLeScanCallback =
            new BluetoothAdapter.LeScanCallback() {
                @Override
                public void onLeScan(final BluetoothDevice bluetoothDevice, int rssi,
                                     byte[] scanRecord) {
                    getActivity().runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            bluetoothDeviceArrayAdapter.add(bluetoothDevice);
                            bluetoothDeviceArrayAdapter.notifyDataSetChanged();
                        }
                    });
                }
            };
    if (enable) {
        // Stops scanning after a pre-defined scan period.
        mHandler.postDelayed(() -> {
            mScanning = false;
            mBluetoothAdapter.stopLeScan(mLeScanCallback);
        }, SCAN_PERIOD);

        mScanning = true;
        mBluetoothAdapter.startLeScan(mLeScanCallback);
    } else {
        mScanning = false;
        mBluetoothAdapter.stopLeScan(mLeScanCallback);
    }

}

Third

Every time you need to scan devices you surround your code asking which version you are. For instance, I have a RefreshLayout to display the list of devices. Here's the result:

  /**
 * Refresh listener
 */
private void refreshScan() {
    if (!hasFineLocationPermissions()) {
        swipeRefreshLayout.setRefreshing(false);


        //Up to marshmallow you need location permissions to scan bluetooth devices, this method is not here since is up to you to implement it and it is out of scope of this question. 
        requestFineLocationPermission();

    } else {
        swipeRefreshLayout.setRefreshing(true);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            scanLeDevice21(true);
        } else {
            scanLeDevice18(true);
        }
    }
}

And that's it.

Forget about extending, subclassing classes you don't really need like ulusoyca answer.