Motorola EMDK : How to stop scanning data on status change?

Question

Background:

I am using the Motorola EMDK v2.5 for .NET to get rfid scan data from an MC 919Z handheld scanner. I want to keep on getting the rfid tag data as long as the user hasthe button on the device pressed. As soon as he removes his finger from the button, I want to stop reading RFID data.

eMDK events I am using:

Now Motorola exposed two events:

• StatusNotify : Event that fires on button status (pressed or not) changes.
• ReadNotify : Event that fires for reading rfid tags.

The issue:

The two events seem to pre-empt each other from being triggerred. If the tags are being read, the button status change event doesn't fire. If the button status change event is firing, the tags aren't read.

So, the question is how can I ensure that both events are fired in tandem.

Answer 1

You will need to do a few things (sorry for the VB code, but should be trivial to convert to C#):

• Whether you are using Actions.Inventory.Perform() or Actions.TagAccess.OperationSequence.PerformSequence() you will need a TriggerInfo defined and passed on to those methods, instead of the regular no-arguments call. This structure contain the actual trigger events.

  Imports Symbol
  Imports Symbol.RFID3
  Imports Symbol.RFID3.Events
  Imports Symbol.RFID3.TagAccess
  
  Private Sub DoRead()
      triggernfo = New TriggerInfo()
      triggernfo.TagReportTrigger = 1
      triggernfo.StartTrigger.Type = START_TRIGGER_TYPE.START_TRIGGER_TYPE_HANDHELD
      triggernfo.StartTrigger.Handheld.HandheldEvent = HANDHELD_TRIGGER_EVENT_TYPE.HANDHELD_TRIGGER_PRESSED
      triggernfo.StopTrigger.Type = STOP_TRIGGER_TYPE.STOP_TRIGGER_TYPE_HANDHELD_WITH_TIMEOUT
      triggernfo.StopTrigger.Handheld.HandheldEvent = HANDHELD_TRIGGER_EVENT_TYPE.HANDHELD_TRIGGER_RELEASED
      triggernfo.StopTrigger.Handheld.Timeout = 0 'Default handheld timeout value
  
  'Then you need to pass it to the Perform() OR PerformSequence() call:
      _Reader.Actions.TagAccess.OperationSequence.PerformSequence(Nothing, triggernfo, Nothing)
  'OR
      _Reader.Actions.Inventory.Perform(Nothing, triggernfo, Nothing)
  End Sub
  

The main point is that you don't need to call Perform() or PerformSequence() to start the reading each time now, you simply can define a procedure after Form.Load that connects to the reader and calls Perform() with the trigger in it, and it will automagically only activate when the trigger is used. Depending on the way you have coded, I think you can use your current delegate callbacks as they are, if the Read delegate one uses GetReadTags() (I'm speculating now, because I haven't seen your code).

Lastly, in your Status delegate call you can now catch a Symbol.RFID3.Events.STATUS_EVENT_TYPE.HANDHELD_TRIGGER_EVENT as the EventData. If you dig further you have inside the eventData.HandheldTriggerEventData.HandheldTriggerEvent that can be HANDHELD_TRIGGER_EVENT_TYPE.HANDHELD_TRIGGER_PRESSED or HANDHELD_TRIGGER_EVENT_TYPE.HANDHELD_TRIGGER_RELEASED. It is worth nothing that you DON'T need to do anything with this event to actually read tags, the trigger and the read will happen anyway even if you do nothing here.

Actually, messing with the Event (like stopping or starting the read) might make the trigger throw errors, so unless you have a pressing need (like I had today), go with the TriggerInfo object and leave the Status delegate alone ;)