Xamarin BLE scanning only sometimes - xamarin

Question

I created simple Xamarin.Forms Bluetooth low energy scanning application. As I will use Bluetooth only on Android, I implemented scanning in MainActivity.cs of Android project:
namespace BlankAppXamlXamarinForms.Droid
{
[Activity(Label = "BlankAppXamlXamarinForms", Icon = "#drawable/icon", Theme = "#style/MainTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation)]
public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
{
private BluetoothManager _manager;
App app;
protected override void OnCreate(Bundle bundle)
{
TabLayoutResource = Resource.Layout.Tabbar;
ToolbarResource = Resource.Layout.Toolbar;
base.OnCreate(bundle);
global::Xamarin.Forms.Forms.Init(this, bundle);
app = new App();
var appContext = Application.Context;
_manager = (BluetoothManager)appContext.GetSystemService(BluetoothService);
_manager.Adapter.BluetoothLeScanner.StartScan(new MyScanCallback(app));
LoadApplication(new App());
}
}
public class MyScanCallback : ScanCallback
{
App _app;
public MyScanCallback(App app) {
_app = app;
}
public override void OnScanResult(ScanCallbackType callbackType, ScanResult result)
{
_app.newDevice(result.Device.Name + " - " + result.Device.Address);
}
}
}
The problem is that OnScanResult receives advertising packets only a moment after the application is started and when I switch the display of my phone off and then turn it on again. Meanwhile the application receives almost no advertising packets. How to receive advertising packets all the time my application is active?

Answer 1

You are creating two instances of App. Instead of LoadApplication(new App()); you should be passing in your field app, i.e. LoadApplication(app);
Also, instead of starting the scan in OnCreate, you might want to start the scan in OnResume and stop the scan in OnPause e.g.:
public class MainActivity : FormsAppCompatActivity
{
BluetoothManager bleManager;
App app;
ScanCallback scanCallback;
protected override void OnCreate(Bundle bundle)
{
TabLayoutResource = Resource.Layout.Tabbar;
ToolbarResource = Resource.Layout.Toolbar;
base.OnCreate(bundle);
Forms.Init(this, bundle);
app = new App();
bleManager = (BluetoothManager)Application.Context.GetSystemService(BluetoothService);
scanCallback = new MyScanCallback(app);
LoadApplication(new App());
}
protected override void OnResume()
{
base.OnResume();
bleManager.Adapter.BluetoothLeScanner.StartScan(scanCallback);
}
protected override void OnPause()
{
base.OnPause();
bleManager.Adapter.BluetoothLeScanner.StopScan(scanCallback);
}
}