Secondary Screen Support Using DisplayManager

Secondary Screen
Support Using
DisplayManager
Copyright © 2013 CommonsWare, LLC

Who's On Second?
●

Auxiliary screen

●

Inconsistently available

●

Display-only (no touchscreen)

●

Not:
–

Simply being on a TV (think OUYA)

–

Devices with dual primary displays (SONY Tablet
P)

Getting To Second: Sending
●

HDMI

●

Mobile High-Definition Link (MHL, SlimPort)

●

Proprietary Cable

●

Miracast/AllShare Cast
–

WifiDirect-based display protocol

–

Available on many modern devices, including most of
the Samsung Galaxy line

Getting to Second: Receiving
●

HDMI
–
–

●

Direct
Via MHL adapter

Miracast/AllShare Cast
–

Direct (e.g., most of Samsung Smart TVs)

–

Via HDMI adapter


Secondary Display: What Is Shown
●

Android 1.0 through 2.3
–
–

●

Generally nothing
Sporadic device-specific support (e.g., HTC DROID
Incredible and composite output)

Android 3.0 through 4.1
–
–

●

Mirroring
Some limited developer control (video players)

Android 4.2+: Developer Control
–

At least for devices that shipped with 4.2+

Not All Screens Are Created Equal
●

Key Differences
–
–

●

Size (720p, 1080p, etc.)
Density (tvdpi, hdpi, etc.)

Net: Different Context for Different Display
–

Inflate layouts, load resources, etc. using proper
Context to get the right ones for the targeted
display

Exerting Your Control
●

Presentation
–

Subclass of Dialog, added in API Level 17

–

Override onCreate(), call
setContentView()

–

Supplies Context suitable for use with
designated Display

–

When displayed using show(), appears on
designated Display

Exerting Your Control
●

CWAC-Presentation and PresentationHelper
–

Lets you know when a secondary display
becomes available or goes away

–

Usage
●

Create instance

●

Supply a Context and a Listener

●

Forward onPause() / onResume()

●

Implement showPreso() /
clearPreso()

Trying It Out
●

Testing Options
–

Actual “secondary screen”

–

Simulated secondary display
●

Developer Options → Simulate secondary displays

●

Works well with hardware, less so with x86 emulator


Low-Level Exertion
●

DisplayManager
–

System service (DISPLAY_SERVICE)

–

getDisplays() (all or those in a category, like
DISPLAY_CATEGORY_PRESENTATION)

–

registerDisplayListener() to find out
about changes in mix of displays

–

New to API Level 17

Low-Level Exertion
●

MediaRouter
–

System service (MEDIA_ROUTER_SERVICE)

–

More general: find preferred “route” for audio or
video

–

getSelectedRoute() to find the route to be
used right now (ROUTE_TYPE_LIVE_VIDEO)

–

addCallback() to find out route changes

–

Added in API Level 16

Fragments of a Presentation
●

Good News!
–

–

●

Presentation extends Dialog, so
DialogFragment works
DialogFragment supports either
show-as-dialog or show-as-regular-fragment

Bad News!
–

Since different Contexts, cannot use the same
DialogFragment instance for each

Secondary Screen Strategies
●

Secondary Screen: Not a Touchscreen
–

●

Whatever shows on secondary screen is driven
and controlled by what is on the primary screen

Example: Video Player
–

Second screen shows the video playback

–

Primary screen has play/pause, fast-forward,
rewind, SeekBar, IMDB content, chat screen, etc.

Secondary Screen Strategies
●

Must Have Secondary Screen
–

●

Optional, Dedicated UX
–

●

Presentation-specific app
Game using second screen for primary output,
device screen for control surface and secondary
output

Optional, Using Fragments
–

Push stuff to second screen or show “inline”

Secondary Screen Tactics
●

Separate Fragments/Views
–
–

●

One for what is shown
One for controlling what is shown

Mirroring Content
–

Same fragment/view, shown on both displays,
controlled by primary screen


Limitations and Annoyances
●

Activity-Based
–

Presentation extends Dialog, must have an
activity to show a Dialog

–

Cannot have second screen driven by service,
with primary screen running something
independent

–

Samsung, multi-window apps, and secondary
screens?

Limitations and Annoyances
●

Activity-Based
–

Must dismiss() Presentation as part of
switching to a new activity → flicker
●

Briefly shows mirroring before new Presentation
appears

–

Similar flicker if you try switching from one
Presentation to another

–

General rule: one activity and one
Presentation, just updating content

Secondary Screen Support Using DisplayManager

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