Basics of touch input
Flash Player 10.1 and later, Adobe AIR 2 and
later
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When the Flash Platform is running in an environment that supports
touch input, InteractiveObject instances can listen for touch events
and call handlers. Generally, you handle touch, multitouch, and
gesture events as you would other events in ActionScript (see
Handling events
for basic information about event handling with ActionScript).
However, for the Flash runtime to interpret a touch or gesture,
the runtime must be running in a hardware and software environment
that supports touch or multitouch input. See
Discovering input types
for a chart comparing different touch screen
types. Additionally, if the runtime is running within a container application
(such as a browser), then that container passes the input to the runtime.
In some cases, the current hardware and operating system environment support
multitouch, but the browser containing the Flash runtime interprets
the input and does not pass it on to the runtime. Or, it can simply
ignore the input altogether.
The following diagram shows the flow of input from user to runtime:
Fortunately, the ActionScript API for developing touch applications
includes classes, methods, and properties to determine the support
for touch or multitouch input in the runtime environment. The API
you use to determine support for touch input are the “discovery
API” for touch event handling.
Important concepts and terms
The following
reference list contains important terms for writing touch event-handling
applications:
-
Discovery API
-
The methods and properties used to test the runtime environment
for support of touch events and different modes of input.
-
Touch event
-
An input action performed on a touch-enabled device using
a single point of contact.
-
Touch point
-
The point of contact for a single touch event. Even if a
device does not support gesture input, it might support multiple
simultaneous touch points.
-
Touch sequence
-
The series of events representing the lifespan of a single
touch. These events include one beginning, zero or more moves, and
one end.
-
Multitouch event
-
An input action performed on a touch-enabled device using several
points of contact (such as more than one finger).
-
Gesture event
-
An input action performed on a touch-enabled device tracing some
complex movement. For example, one gesture is touching a screen
with two fingers and moving them simultaneously around the perimeter
of an abstract circle to indicate rotation.
-
Phases
-
Distinct points of time in the event flow (such as begin
and end).
-
Stylus
-
An instrument for interacting with a touch-enabled screen.
A stylus can provide more precision than the human finger. Some
devices recognize only input from a specific type of stylus. Devices
that do recognize stylus input might not recognize multiple, simultaneous
points of contact or finger contact.
-
Press-and-tap
-
A specific type of multitouch input gesture where the user pushes
a finger against a touch-enabled device and then taps with another finger
or pointing device. This gesture is often used to simulate a mouse
right-click in multitouch applications.
The touch input API structure
The ActionScript touch input API is designed to address
the fact that touch input handling depends on the hardware and software
environment of the Flash runtime. The touch input API primarily
addresses three needs of touch application development: discovery,
events, and phases. Coordinate these API to produce a predictable
and responsive experience for the user; even if the target device
is unknown as you develop an application.
Discovery
The discovery API provides the ability to test the hardware
and software environment at runtime. The values populated by the
runtime determine the touch input available to the Flash runtime
in its current context. Also, use the collection of discovery properties
and methods to set your application to react to mouse events (instead
of touch events in case some touch input is not supported by the
environment). For more information, see
Touch support discovery
.
Events
ActionScript manages touch input events with event listeners
and event handlers as it does other events. However, touch input
event handling also must take into account:
-
A touch can
be interpreted in several ways by the device or operating system, either
as a sequence of touches or, collectively, as a gesture.
-
A single touch to a touch-enabled device (by a finger, stylus
or pointing device) always dispatches a mouse event, too. You can
handle the mouse event with the event types in the MouseEvent class.
Or, you can design your application only to respond to touch events.
Or, you can design an application that responds to both.
-
An application can respond to multiple, simultaneous touch
events, and handle each one separately.
Typically, use the discovery API to conditionally handle the
events your application handles, and how they are handled. Once
the application knows the runtime environment, it can call the appropriate
handler or establish the correct event object when the user interacts
with the application. Or, the application can indicate that specific
input cannot be handled in the current environment and provide the
user with an alternative or information. For more information, see
Touch event handling
and
Gesture event handling
.
Phases
For touch and multitouch applications, touch event objects
contain properties to track the phases of user interaction. Write
ActionScript to handle phases like the begin, update, or end phase
of user input to provide the user with feedback. Respond to event
phases so visual objects change as the user touch and moves the
point of touch on a screen. Or, use the phases to track specific
properties of a gesture, as the gesture evolves.
For touch point events, track how long the user rests on a specific
interactive object. An application can track multiple, simultaneous
touch points’ phases individually, and handle each accordingly.
For a gesture, interpret specific information about the transformation
of the gesture as it occurs. Track the coordinates of the point
of contact (or several) as they move across the screen.
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