Grabba Driver for Android
Unified driver for Grabba devices on the Android operating system
MRTD_Listener Class Reference

Description

Base class for receiving events related to reading of Machine-Readable Zones (MRTDs)

The following events are supported by this class:

  • dataEvent - MRTD data was read (i.e. read operation completed successfully)
  • errorEvent - MRTD read operation encountered an error (e.g. loss of connection)
  • progressEvent - progress update on an active MRTD read operation

Each event may invoke callbacks in two ways:

  • Subclassing - the relevant event methods (e.g. dataEvent) are called directly
    • This approach is recommended wherever feasible, due to its simplicity
    • To use it, create an object of a suitable subclass, which overrides the desired event method(s)
  • Delegation - event methods trigger method calls for a delegate object
    • This approach is only recommended when the callback handler must inherit from a different base class
    • To use it, create an object of this class, create an object of a class which implements MRTD_Interface, then call setDelegate() to provide the necessary linkage.
Note
Delegation will be disabled for an event if that event's method is subclassed, unless the subclass calls the superclass' equivalent method from within its override thereof.

By default, each listener object will receive event notifications from the driver for its entire lifetime; the enable() and disable() methods may be used if control is required over whether notifications are received.

The default behaviour for each event, if not overridden, on an enabled listener object is as follows:

  • If setDelegate() has not been called, then take no action
  • If the last call to setDelegate() accepted a null reference, then take no action
  • If the last call to setDelegate() accepted a non-null object reference, then delegate to that object

Overrides need not call the superclass' equivalent method unless it is necessary to preserve the delegation (i.e. to support both subclassing and delegation from a single object).

Thread safety: This class is intended to be thread-safe; any classes deriving from it should ensure that the relevant methods are callable from any thread.

See also
MRTD_API for related API functions
Inheritance diagram for MRTD_Listener:
Listener< Delegate > MRTD_Interface

Public Member Functions

 MRTD_Listener ()
 Default constructor - builds a listener object then enables receipt of events from the driver.
 
 MRTD_Listener (boolean startEnabled)
 Constructor - builds a listener object then optionally enables receipt of events from the driver. More...
 
void dataEvent (@NonNull BER_TLV data)
 Callback which is invoked when an asynchronous MRTD read completes successfully. More...
 
final void disable ()
 Disable receipt of events from the driver by this object. More...
 
final void enable ()
 Enable receipt of events from the driver by this object. More...
 
void errorEvent (@NonNull ErrorCode error)
 Callback which is invoked when an asynchronous MRTD read fails. More...
 
void progressEvent (byte percentage)
 Callback which is invoked when asynchronous MRTD read progress advances. More...
 
final void setDelegate (Delegate newDelegate)
 Set the delegate which will receive event callbacks if default listener behaviour is not overridden. More...
 

Constructor & Destructor Documentation

◆ MRTD_Listener()

MRTD_Listener ( boolean  startEnabled)

Constructor - builds a listener object then optionally enables receipt of events from the driver.

Parameters
startEnabledIf set, the listener object is enabled immediately (equivalent of default constructor), otherwise it is disabled until the first call to enable()

Member Function Documentation

◆ dataEvent()

void dataEvent ( @NonNull BER_TLV  data)

Callback which is invoked when an asynchronous MRTD read completes successfully.

This event will be triggered by the driver when an asynchronous MRTD read operation completes successfully, providing the listener object is enabled.

Override this method to receive callbacks when the object is enabled (at construction or via enable()) and the event is triggered.

Note
Overrides of this method are required to be thread-safe; no guarantees are made about which thread(s) they will be called from.
Parameters
dataContents of the data read from the MRTD, in BER-TLV format

Implements MRTD_Interface.

◆ disable()

final void disable ( )
inherited

Disable receipt of events from the driver by this object.

This has no effect if the object was already disabled.

◆ enable()

final void enable ( )
inherited

Enable receipt of events from the driver by this object.

This has no effect if the object was already enabled.

◆ errorEvent()

void errorEvent ( @NonNull ErrorCode  error)

Callback which is invoked when an asynchronous MRTD read fails.

This event will be triggered by the driver when an asynchronous MRTD read operation fails, providing the listener object is enabled.

Override this method to receive callbacks when the object is enabled (at construction or via enable()) and the event is triggered.

Note
Overrides of this method are required to be thread-safe; no guarantees are made about which thread(s) they will be called from.
Parameters
errorReason why the read operation failed

Implements MRTD_Interface.

◆ progressEvent()

void progressEvent ( byte  percentage)

Callback which is invoked when asynchronous MRTD read progress advances.

This event will be triggered by the driver at regular intervals during asynchronous MRTD read operations, providing the listener object is enabled.

Override this method to receive callbacks when the object is enabled (at construction or via enable()) and the event is triggered.

Note
Overrides of this method are required to be thread-safe; no guarantees are made about which thread(s) they will be called from.
Parameters
percentageCurrent read progress percentage

Implements MRTD_Interface.

◆ setDelegate()

final void setDelegate ( Delegate  newDelegate)
inherited

Set the delegate which will receive event callbacks if default listener behaviour is not overridden.

Delegation may alternatively be disabled by providing a null reference here.

Parameters
newDelegateIf null, disables delegation; if non-null, enables delegation and sets the delegate to the supplied object.