Question

I’m working on a mobile application (C#/WPF on a tablet PC) that prints to a bluetooth connected printer. Right now I just fire off a print job, and if the printer is not present the printer subsystem reports an error to the user. I’m not doing anything programatically with Bluetooth, just using PrintDialog().

I’d like to modify this process to detect the printer first – if it is not available, then I’ll just store the document without printing. Is there a way in code for me to detect if the bluetooth device is connected/active/available?

If I look at the device in the Bluetooth panel under Control Panel, it doesn’t seem to have any sort of status that reflects whether or not the device is available, so maybe this isn’t possible.

I’m assuming the printer has already been setup and configured in Windows – all I need to do is detect if it is actually present at a given point in time.

Answer 1

Perhaps use the 32feet.NET library (of which I am the maintainer) and check if the printer is present before submitting the job. You’d need to know the Bluetooth address of the printer; can one get that from the system, or maybe you always know it.

Discovery on the MSFT Bluetooth stack always returns all known devices in amongst those in range 🙁 but we can use other means to detect the device’s presence/absence. Perhaps using BluetoothDeviceInfo.GetServiceRecords in its BeginGetServiceRecords form. e.g. something like (not tested/compiled):

bool IsPresent(BluetoothAddress addr) // address from config somehow
{
   BluetoothDeviceInfo bdi = new BluetoothDeviceInfo(addr);
   if (bdi.Connected) {
      return true;
   }
   Guid arbitraryClass = BluetoothService.Headset;
   AsyncResult<bool> ourAr = new AsyncResult<bool>(); // Jeffrey Richter's impl
   IAsyncResult ar = bdi.BeginGetService(arbitraryClass, IsPresent_GsrCallback, ourAr);
   bool signalled = ourAr.AsyncWaitHandle.WaitOne(Timeout);
   if (!signalled) {
      return false; // Taken too long, so not in range
   } else {
      return ourAr.Result;
   }
}

void IsPresent_GsrCallback(IAsyncResult ar)
{
    AsyncResult<bool> ourAr = (AsyncResult<bool>)ar.AsyncState;
    const bool IsInRange = true;
    const bool completedSyncFalse = true;
    try {
       bdi.EndGetServiceResult(ar);
       ourAr.SetAsCompleted(IsInRange, completedSyncFalse);
    } catch {
       // If this returns quickly, then it is in range and
       // if slowly then out of range but caller will have
       // moved on by then... So set true in both cases...
       // TODO check what error codes we get here. SocketException(10108) iirc
       ourAr.SetAsCompleted(IsInrange, completedSyncFalse);
    }
}