Some devices themselves may have multiple screens, such as the Sony Tablet P —
what those devices do with those screens will be up to the device.
Historically, support for external displays was manufacturer-dependent. Early
Android devices had no ability to be displayed on an external display except through
so-called “software projectors” like Jens Riboe’s Droid@Screen. Some Android 2.x
devices had ports that allowed for HDMI or composite connections to a television or
projector. However, control for what would be displayed resided purely in the hands
of the manufacturer. Some manufacturers would display whatever was on the
touchscreen (a.k.a., “mirroring”). Some manufacturers would do that, but only for
select apps, like a built-in video player.
Android 3.0 marked the beginning of Android’s formal support for external displays,
as the Motorola XOOM supported mirroring of the LCD’s display via an micro-
HDMI port. This mirroring was supplied by the core OS, not via device-dependent
means. Any Android 3.0+ device with some sort of HDMI connection (e.g., micro-
HDMI port) should support this same sort of mirroring capability.
However, mirroring was all that was possible. There was no means for an application
to have something on the external display (e.g., a video) and something else on the
primary screen (e.g., playback controls plus IMDB content about the movie being
watched).
Android 4.2 changed that, with the introduction of Presentation.
What is a Presentation?
A Presentation is a container for displaying a UI, in the form of a View hierarchy
(like that of an activity), on an external display.
You can think of a Presentation as being a bit like a Dialog in that regard. Just as a
Dialog shows its UI separate from its associated activity, so does a Presentation. In
fact, as it turns out, Presentation inherits from Dialog.
The biggest dierence between a Presentation and an ordinary Dialog, of course, is
where the UI is displayed. A Presentation displays on an external display; a Dialog
displays on the primary screen, overlaying the activity. However, this dierence has a
profound implication: the characteristics of the external display, in terms of size and
density, are likely to be dierent than those of a primary screen.
SUPPORTING EXTERNAL DISPLAYS
2
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