Multi-user Programming

EMDK For Android 7.1

Overview

EMDK for Android 7.1 (and higher) supports Android multi-user mode, which allows a device to have Primary and Secondary users, each with its own sets of apps, capabilities and access privileges. When running an EMDK app on a device with multiple users, EMDK is enabled only for the active user. Apps must be designed to release internal device resources and the EMDKManager whenever the app goes to the background and to reacquire them when returning to the foreground. This is done by listening with intents:

  • ACTION_USER_BACKGROUND - release internal resources when heard
  • ACTION_USER_FOREGROUND - reacquire resources when heard

The EMDK service automatically releases external component resources (i.e. scanner, serial and SimulScan objects) when an app goes to the background to make them available to the foreground app. Scanning resources must be programmatically reacquired when the EMDK app returns to the foreground.


Example

The code below demonstrates how an app should release and reacquire EMDK resources when switching users on a device.


public class MainActivity extends Activity implements EMDKListener, DataListener, StatusListener, ScannerConnectionListener {

    private EMDKManager emdkManager = null;
    private BarcodeManager barcodeManager = null;
    private Scanner scanner = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        try {
            IntentFilter filter = new IntentFilter();
            filter.addAction(Intent.ACTION_USER_BACKGROUND);
            filter.addAction(Intent.ACTION_USER_FOREGROUND);
            registerReceiver(broadcastReceiver, filter);

        } catch (Exception ex) {
            ex.printStackTrace();
        }

        EMDKResults results = EMDKManager.getEMDKManager(getApplicationContext(), this);
        if (results.statusCode != EMDKResults.STATUS_CODE.SUCCESS) {
            return;
        }
    }

    BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {

        @Override
        public void onReceive(Context context, Intent intent) {
            boolean appSentToBackground = intent.getAction().equals(Intent.ACTION_USER_BACKGROUND);
            boolean appCameToForeground = intent.getAction().equals(Intent.ACTION_USER_FOREGROUND);

            // TODO MultiUser
            if (appSentToBackground) {

                log("App going to background");

                try {
                    // Release all resources
                    if (emdkManager != null) {
                        emdkManager.release();
                        emdkManager = null;
                    }

                } catch (Throwable e) {
                    e.printStackTrace();
                }

            }

            if (appCameToForeground) {

                log("App coming to foreground");

                // Setting objects to null if background task are interrupted.
                if(scanner != null)
                    scanner = null;

                if(barcodeManager != null)
                    barcodeManager = null;

                if(emdkManager != null)
                    emdkManager = null;

                EMDKResults results = EMDKManager.getEMDKManager(getApplicationContext(), MainActivity.this); 

                // Use a final variable if MainActivity.this (above) fails.
                // If result == SUCCESS, onOpened is called 
                // and scanner object is reacquired
                if (results.statusCode != EMDKResults.STATUS_CODE.SUCCESS) {
                    return;
                }
            }
        }
    };

    @Override
    protected void onDestroy() {
        super.onDestroy();

        try {
            // Release all resources
            if (emdkManager != null) {
                emdkManager.release();
                emdkManager = null;

            }
        }
        catch (Throwable throwable)
        {
            throwable.printStackTrace();
        }
    }

    @Override
    public void onOpened(EMDKManager emdkManager) {

        this.emdkManager = emdkManager;
        log("Initializing EMDK.. Please wait..");

        // Acquire barcode manager resources
        barcodeManager = (BarcodeManager) emdkManager.getInstance(FEATURE_TYPE.BARCODE);
        if(barcodeManager == null)
        {
            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            barcodeManager = (BarcodeManager) emdkManager.getInstance(FEATURE_TYPE.BARCODE);
        }

        // Add connection listener
        if (barcodeManager != null) {
            barcodeManager.addConnectionListener(this);
            initScanner();
        }


    }

    @Override
    public void onClosed() {

        try {
            if (emdkManager != null) {
                // Release all the resources
                emdkManager.release();
                emdkManager = null;
            }
        } catch (Throwable e) {
            e.printStackTrace();
        }
    }

    private void initScanner() {

        if (scanner == null) {

            scanner = barcodeManager.getDevice(BarcodeManager.DeviceIdentifier.DEFAULT);

            if (scanner != null) {

                scanner.addDataListener(this);
                scanner.addStatusListener(this);

                try {
                    scanner.enable();
                } catch (ScannerException e) {

                }
            }
        }
    }


    @Override
    public void onData(ScanDataCollection scanDataCollection) {
        if ((scanDataCollection != null) && (scanDataCollection.getResult() == ScannerResults.SUCCESS)) {
            ArrayList<ScanDataCollection.ScanData> scanData = scanDataCollection.getScanData();
            for(ScanDataCollection.ScanData data : scanData) {

                log("onData: " + data.getData());

            }
        }
    }

    @Override
    public void onStatus(StatusData statusData) {

        StatusData.ScannerStates state = statusData.getState();
        String statusString = statusData.getFriendlyName()+" is " + state.toString().toLowerCase();

        log("Status: "+statusString);

        switch(state) {
            case IDLE:
                try {
                    scanner.read();
                } catch (ScannerException e) {
                    e.printStackTrace();
                    log("Error: " + e.getMessage());
                }
                break;
        }
    }

    @Override
    public void onConnectionChange(ScannerInfo scannerInfo, ConnectionState connectionState) {


    }

    private void log(String message)
    {
        Log.d("TAG","#EMDKMultiuser# " + message);
    }
}