Detecting contactless targets

To communicate with contactless targets, the MIDlet must first determine which types of contactless targets the device supports, and then register a listener that notifies the MIDlet when a supported contactless target is detected. The MIDlet must register a listener separately for each type of contactless target.

To detect contactless targets:

1. Import the required Contactless Communication API packages:

   // packages required for determining supported types and registering a target listener
   import javax.microedition.contactless.ContactlessException;
   import javax.microedition.contactless.DiscoveryManager;
   import javax.microedition.contactless.TargetListener;
   import javax.microedition.contactless.TargetProperties;
   import javax.microedition.contactless.TargetType;

2. Determine the contactless target types supported by the device by using the DiscoveryManager.getSupportedTargetTypes method:

   TargetType[] supportedTargetTypes = DiscoveryManager.getSupportedTargetTypes();

3. Register a TargetListener for a supported contactless target type by using the DiscoveryManager.addTargetListener method. If you want to register the TargetListener for multiple contactless target types, call the method separately for each type.

   The following code snippet creates a custom method that registers a TargetListener for NDEF targets (TargetType.NDEF_TAG).

   public void registerNDEFListener(TargetListener targetListener) {
   
       // determine the contactless target types supported by the device
       TargetType[] supportedTargetTypes = DiscoveryManager.getSupportedTargetTypes();
   
       // check if the NDEF_TAG type is supported by the device,
       // and if it is, register the listener for it
       for (int i=0; i<supportedTargetTypes.length; i++) {
           if (supportedTargetTypes[i].equals(TargetType.NDEF_TAG)) {
               try {
                   // create a DiscoveryManager instance
                   DiscoveryManager discoveryManager = DiscoveryManager.getInstance();
                   // register the specified TargetListener (parameter) for the NDEF_TAG type
                   discoveryManager.addTargetListener(targetListener, TargetType.NDEF_TAG);
               } catch (SecurityException e) {
                   // handle SecurityException from DiscoveryManager.getInstance()
               } catch (ContactlessException e) {
                   // handle ContactlessException from discoveryManager.addTargetListener()
               } catch (IllegalStateException e) {
                   // handle IllegalStateException from discoveryManager.addTargetListener()
               } catch (NullPointerException e) {
                   // handle NullPointerException from discoveryManager.addTargetListener()
               }
               // break the for loop, since a matching target type has been found
               break;
           }
       }
   
   }

Now that you have set the MIDlet to detect contactless targets, define how it communicates with them by implementing the TargetListener.