CWAC Presentation: Second Screen Support Simplified
Java

README.markdown

CWAC-Presentation: Second Screens Supported Succinctly

This project offers a series of classes that wrap around the Presentation and DisplayManager of Android 4.2:

  • PresentationHelper consolidates basic DisplayManager handling, with a listener to inform you when to show or remove your Presentation

  • PresentationFragment extends DialogFragment and adds a bit of extra logic to allow it to handle a Presentation rather than a simple Dialog

  • WebPresentationFragment simply extends PresentationFragment and displays a WebView in the Presentation

  • MirroringFragment, MirroringWebViewFragment, and MirrorPresentationFragment leverage the mirroring logic from the CWAC-Layouts project to help you display a Presentation based upon mirrored content from the main screen

  • PresentationService, for showing content on an external display from the background, even if your primary UI is destroyed or otherwise not in the foreground

Installation

This Android library project is available as a JAR. If you wish to use the JAR, you will need to also add the JAR from the CWAC-Layouts project to your project if you wish to use the Mirror* classes. If you are not using the Mirror* classes, then the CWAC-Presentation JAR is sufficient.

NOTE: The JAR name, as of v0.4.2, has a cwac- prefix, to help distinguish it from other JARs.

Also note that if you plan to use this as an Android library project in source form, you will also need to download the CWAC-Layouts project (and, if needed, modify this project's configuration to point to your copy of CWAC-Layouts' library project). Alternatively, download the CWAC-Layouts JAR into the libs/ directory of your clone of this project and remove the dependency on the CWAC-Layouts library project.

This project is also available as an artifact for use with Gradle. To use that, add the following blocks to your build.gradle file:

repositories {
    maven {
        url "https://s3.amazonaws.com/repo.commonsware.com"
    }
}

dependencies {
    compile 'com.commonsware.cwac:presentation:0.4.+'
}

Or, if you cannot use SSL, use http://repo.commonsware.com for the repository URL. This should automatically pull down the CWAC-Layouts dependency.

Usage: PresentationHelper

PresentationHelper is designed to be used by an Activity that wishes to display a Presentation when a suitable Display is attached, and stop displaying the Presentation when any prior such Display is detached.

To do this:

  • Create an instance of PresentationHelper, probably in onCreate() of the activity. You will need to supply a Context (probably this) and something that implements the PresentationHelper.Listener interface.

  • Forward the onPause() and onResume() events to the PresentationHelper by calling the same-named methods on the helper.

  • Implement the showPreso() method on your Listener. This receives a Display object, and you are now able to display a Presentation on that Display.

  • Implement the clearPreso() method on your Listener. At this point, you should stop displaying any prior Presentation, if there was one. You are passed a boolean value, true indicating that the activity is going away, false indicating that we merely lost our Display. You can use this value to perhaps optimize dealing with Display changes, without destroying all the data.

You can call disable() and enable() on the PresentationHelper. Calling disable() stops the custom content and reverts the device to normal screen mirroring mode. Calling enable() reverts a previous disable() call.

Usage: PresentationFragment

PresentationFragment is a thin veneer over DialogFragment to allow it to work with Presentation objects (which themselves inherit from Dialog). This allows you to define the content for a Presentation in the form of a fragment. And, like DialogFragment, you can elect to either use it for a Presentation (via a call to show()) or use it as an ordinary Fragment in the rest of your UI (via a FragmentTransaction). This can help you to work both in dual-screen and single-screen scenarios.

Your PresentationFragment subclass should override onCreateView() to define the contents of the Presentation (or what will be shown in the Fragment when used as a regular fragment). The only significant change over any other Fragment is that you should use getContext(), instead of getActivity(), for any resources you create, such as inflating a layout. This ensures that you get the right Context for the situation, such as the Context associated with a secondary screen when used for a Presentation.

However, when creating the PresentationFragment, you also need to call setDisplay(), to provide the Display object for use when the fragment is shown as a Presentation. If you are not using it for a Presentation in the current context, this call is not required. A typical approach for handling setDisplay() is to use a factory method:

public static YourFragment newInstance(Context ctxt, Display display) {
  YourFragment frag=new YourFragment();

  frag.setDisplay(ctxt, display);

  return(frag);
}

Beyond this, PresentationFragment is a fairly ordinary Fragment.

If you wish to display this fragment in a Presentation, call show() on the PresentationFragment, supplying your FragmentManager and a tag to use for the fragment itself. To get rid of the Presentation, call dismiss() on the PresentationFragment.

Usage: WebPresentationFragment

WebPresentationFragment is simply a mash-up of PresentationFragment and WebViewFragment, to allow a WebView to be displayed in a Presentation. You use it just like WebViewFragment, except for the need to call setDisplay() (per the PresentationFragment instructions above). So, for example, getWebView() returns the WebView hosted by the WebPresentationFragment.

Usage: Mirroring Presentation Classes

There are three classes that take advantage of the mirroring support included in the CWAC-Layouts project.

MirroringFragment works much like a regular Fragment. However, instead of overriding onCreateView(), you override onCreateMirroredContent(). onCreateMirroredContent() takes the same parameters as does onCreateView(), and your job is the same: create the content to be displayed by the fragment. The difference is that your returned View will be wrapped in a MirroringFrameLayout.

MirroringWebViewFragment is a mash-up of MirroringFragment and WebViewFragment, to allow a WebView to be mirrored. Use getWebView() to retrieve the WebView hosted by this fragment.

MirrorPresentationFragment is a PresentationFragment designed to mirror the contents of a MirroringFragment. To use this, create an instance using the newInstance() factory method, taking a Context and the desired Display as parameters. Then, call setMirror() on your MirroringFragment, supplying the MirrorPresentationFragment. From there, you can show() and dismiss() the MirrorPresentationFragment as you would any other PresentationFragment. By having the MirroringFragment on the main screen, and having the MirrorPresentationFragment on an external display, whatever the user manipulates on the screen is rendered to the external display, ideal for presentation settings (e.g., conferences).

Note that MirroringFragment suffers the same limitations as does MirroringFrameLayout, in that it will work with fairly ordinary Views, plus WebView, but not SurfaceView or things that use SurfaceView (e.g., VideoView, Maps V2 maps).

Usage: PresentationService

PresentationService is an abstract base class for you to extend, where PresentationService handles showing your content on an external display, and you simply manage that content.

In your PresentationService subclass, you will need to implement two methods:

  • getThemeId(), which returns the ID of the style resource that you want to use for content being shown on the external display.

  • buildPresoView(), which returns the View that represents the content to show on the external display. Note that since this is a Service, not an Activity, you cannot use fragments, only views. buildPresoView() is passed a Context and a LayoutInflater for your use to set up the content to be displayed.

You may optionally override the standard lifecycle methods (though please chain to the superclass!) and buildLayoutParams(), which returns a WindowManager.LayoutParams describing how your View should be applied to the external display. The default implementation of buildLayoutParams() is probably adequate for your needs.

You may also optionally override the showPreso() and clearPreso() methods defined by PresentationHelper.Listener, though, once again, please chain to the superclass implementations.

Then, all you need to do is to arrange to start and stop the service as needed. Once started, the service will automatically call buildPresoView() and show the content, once an external display is detected.

If things that the user does in your UI should affect the behavior of the service and its content, use a message bus implementation, such as:

  • LocalBroadcastManager
  • Square's Otto
  • greenrobot's EventBus

Your PresentationService can receive bus messages and update the View accordingly. Note that there is no present means to replace the View, so you may wish to have buildPresoView() return a FrameLayout or something else whose contents you can replace in toto if needed.

Note that it is safe to call startService() on the service multiple times, if you do not know whether the service is already running and need to ensure that it is running now.

Dependencies

This project depends on Android 4.2 and higher (API Level 17) to actually do its work. It should survive on older devices, simply doing nothing.

This project also depends upon the CWAC-Layouts project.

Version

This is version v0.4.5 of this module, meaning it is coming along nicely.

Demo

In the demo/ sub-project you will find a sample project demonstrating the use of the aforementioned classes, with the exception of PresentationService. There is a separate demoService/ sub-project with a sample implementation of PresentationService.

Additional Documentation

The Busy Coder's Guide to Android Development contains a chapter dedicated to the Presentation API. This chapter walks through a few sample apps that use classes from this library. Another chapter in the book examines a somewhat larger app that supports output on TVs, etc. by a variety of means (e.g., direct-to-TV devices like Android TV and Fire TV) including Presentation and this library's classes.

License

The code in this project is licensed under the Apache Software License 2.0, per the terms of the included LICENSE file.

Questions

If you have questions regarding the use of this code, please post a question on StackOverflow tagged with commonsware-cwac and android after searching to see if there already is an answer. Be sure to indicate what CWAC module you are having issues with, and be sure to include source code and stack traces if you are encountering crashes.

If you have encountered what is clearly a bug, or if you have a feature request, please post an issue. The contribution guidelines provide some suggestions for how to create a bug report that will get the problem fixed the fastest.

Do not ask for help via Twitter.

Also, if you plan on hacking on the code with an eye for contributing something back, please open an issue that we can use for discussing implementation details. Just lobbing a pull request over the fence may work, but it may not. Again, the contribution guidelines provide a bit of guidance here.

Release Notes

  • v0.4.5: got PresentationService working again on Android 5.1
  • v0.4.4: updated for Android Studio 1.0 and new AAR publishing system
  • v0.4.3: removed SYSTEM_ALERT_WINDOW permission requirement
  • v0.4.2: updated Gradle, fixed manifest for merging, added cwac- prefix to JAR
  • v0.4.1: tweak for v0.4.0 of CWAC-Layouts
  • v0.4.0: added PresentationService
  • v0.3.0: migrated to Gradle
  • v0.2.0: handle API level diffs, support enable/disable of PresentationHelper
  • v0.1.0: initial release

Who Made This?

CommonsWare