I recently ran into an interesting issue with the code for the FindTheMonkey iBeacon app. Previously I had the code for the app to act as an iBeacon using a CBPeripheralManager, which I created in the ViewDidLoad method. This previously worked fine but someone ran into an issue where ranging for the beacon never discovered it. To resolve this involved a couple small changes:

1. Move the creation of the CBPeriheralManager into the constructor.

peripheralDelegate = new BTPeripheralDelegate ();

peripheralMgr = new CBPeripheralManager (
  peripheralDelegate, 
  DispatchQueue.DefaultGlobalQueue);

2. Call the StartAdvertising method in ViewDidAppear.

public override void ViewDidAppear (bool animated)
{
  base.ViewDidAppear (animated);

  var power = new NSNumber (-59);
  peripheralData = beaconRegion.GetPeripheralData (power);
  peripheralMgr.StartAdvertising (peripheralData);
} 

With these changes in place, ranging for the beacon discovers it as it had before: