ButtonListener Class Reference

Description

Base class for receiving events when Grabba device buttons are pressed or released.

The following events are supported by this class:

• leftButtonEvent - left button was pressed or released
• rightButtonEvent - right button was pressed or released

Each event may invoke callbacks in two ways:

• Subclassing - the relevant event methods (e.g. leftButtonEvent) 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 ButtonInterface, 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

ButtonAPI for related API functions

Inheritance diagram for ButtonListener:

Public Member Functions
	ButtonListener ()
	Default constructor - builds a listener object then enables receipt of events from the driver.
	ButtonListener (boolean startEnabled)
	Constructor - builds a listener object then optionally enables receipt of events from the driver. 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	leftButtonEvent (boolean pressed)
	Callback which is invoked when a connected Grabba device's left button is pressed or released. More...
void	rightButtonEvent (boolean pressed)
	Callback which is invoked when a connected Grabba device's right button is pressed or released. 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

ButtonListener()

ButtonListener

(

boolean

startEnabled

)

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

Parameters

startEnabled

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

Member Function Documentation

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.

leftButtonEvent()

void leftButtonEvent

(

boolean

pressed

)

Callback which is invoked when a connected Grabba device's left button is pressed or released.

This method will be triggered by the driver when there is a connected Grabba device, the left button of that device transitions between the pressed and released states, and 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

pressed

Set true if this event indicates a button press; false if it indicates a button release

Implements ButtonInterface.

rightButtonEvent()

void rightButtonEvent

(

boolean

pressed

)

Callback which is invoked when a connected Grabba device's right button is pressed or released.

This method will be triggered by the driver when there is a connected Grabba device, the right button of that device transitions between the pressed and released states, and 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

pressed

Set true if this event indicates a button press; false if it indicates a button release

Implements ButtonInterface.

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

newDelegate

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