public class ShakeActivity extends AppCompatActivity
{
    private static final int VPN_REQUEST_CODE = 0x0F;

    private boolean waitingForVPNStart;

    private BroadcastReceiver vpnStateReceiver = new BroadcastReceiver()
    {
        @Override
        public void onReceive(Context context, Intent intent)
        {
            if (LocalVPNService.BROADCAST_VPN_STATE.equals(intent.getAction()))
            {
                if (intent.getBooleanExtra("Berjalan", false))
                    waitingForVPNStart = false;
            }
        }
    };

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

        final Button vpnButton = (Button)findViewById(R.id.vpn);
        vpnButton.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v)
            {
                startVPN();
            }
        });
        waitingForVPNStart = false;
        LocalBroadcastManager.getInstance(this).registerReceiver(vpnStateReceiver,
                new IntentFilter(LocalVPNService.BROADCAST_VPN_STATE));
    }

    private void startVPN()
    {
        Intent vpnIntent = VpnService.prepare(this);
        if (vpnIntent != null)
            startActivityForResult(vpnIntent, VPN_REQUEST_CODE);
        else
            onActivityResult(VPN_REQUEST_CODE, RESULT_OK, null);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data)
    {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == VPN_REQUEST_CODE && resultCode == RESULT_OK)
        {
            waitingForVPNStart = true;
            startService(new Intent(this, LocalVPNService.class));
            enableButton(false);
        }
    }

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

        enableButton(!waitingForVPNStart && !LocalVPNService.isRunning());
    }

    private void enableButton(boolean enable)
    {
        final Button vpnButton = (Button) findViewById(R.id.vpn);
        if (enable)
        {
            vpnButton.setEnabled(true);
            vpnButton.setText(R.string.start_vpn);
        }
        else
        {
            vpnButton.setEnabled(false);
            vpnButton.setText(R.string.stop_vpn);
        }
    }
}