Android Bits

I'm Peter Tran, an Android developer based in San Diego. I'm using this blog to keep track of the bits of info I'm learning along the way.

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Peter Tran's profile on Hashnode. Software Developer at GoPro

Trying out Hashnode’s Devblog, check me out over there: https://hashnode.com/@petertran

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Byobu and Screen

As I dive back into Linux userspace development I rediscovered Byobu and GNU Screen. These are terminal multiplexer tools, giving me tabs to different terminals plus session management.

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Delivering results from Service to Activity

Activity creates Intent for Service and can insert ResultReceiver as Extra.

But what if Activity is stopped before result sent to RR?

Better to use LocalBroadcastManager

Here’s a good post on different ways to launch worker tasks: http://techtej.blogspot.com.es/2011/03/android-thread-constructspart-4.html?m=1

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Same service defined in multiple apps

I have multiple apps using a service that is defined in a common SDK. So adding the service in each app's manifest uses the same package name.

This is fine because by default the interface to the service is not exported:

http://developer.android.com/guide/topics/manifest/service-element.html#exported

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Cross-client Identity

After coding up some sample implementation I realize that the instructions for Cross-client Identity are actually two slightly different flows.

Both involve the Google auth server and your two clients, the Android app and the web app. The Android app is retrieving a piece of information from Google and forwarding it to the web app.

The two flows differ in what the piece of information is that is being forwarded to web app; it is either

a confirmed identity (email address); or

a one-time use auth code that web app exchanges for an OAuth access token.

Use flow (1) when the web app just needs an email address (signed by Google).

Use flow (2) when the web app will be accessing the user's Google account on behalf of the Android app (ie to retrieve more account info beyond email address).

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Removing ActionBar and Status bar

This will cause crash on orientation change on 4.2 and lower:

getWindow().requestFeature(Window.FEATURE_NO_TITLE);

instead use

getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN); getActionBar().hide();

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Programmatic Orientation Change

Great for semi-automated testing:

private int mOrientationChangeCount; private Runnable mOrientationChangeRunnable = new Runnable() { @Override public void run() { Context context = getContext(); if (context instanceof Activity) { Activity activity = ((Activity)context); if ((++mOrientationChangeCount % 2) > 0) { activity.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE); } else { activity.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT); } } postDelayed(mOrientationChangeRunnable, 5000); } };

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TestFlight Replacement

Publish to a shared Dropbox folder.

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Google Play Services Library

From http://developer.android.com/google/play-services/setup.html

Make a copy of the Google Play services library project.

Note: If you are using Android Studio, skip this step.

Copy the library project at /extras/google/google_play_services/libproject/google-play-services_lib/ to the location where you maintain your Android app projects.

If you are using Eclipse, import the library project into your workspace. Click File > Import, select Android > Existing Android Code into Workspace, and browse to the copy of the library project to import it.

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GoogleApiClient

When using GoogleApiClient for the first time you will probably see the following logcat error:

GLSActivity(1108): [apc] Status from wire: INVALID_CLIENT_ID status: null GLSUser(1108): GLS error: INVALID_CLIENT_ID [email protected] oauth2:https://www.googleapis.com/auth/plus.login

Solution

In the Developer Console you need to manually enter a Consent message; see this StackOverflow answer.

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Google+ Sign In

Getting started with Google+ integration:

https://developers.google.com/+/quickstart/android

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Retrofit - Java REST Adapter

http://square.github.io/retrofit/

Manages the HTTP client

Marshals POJOs back and forth from JSON

Easy setting of OAuth2 tokens as a HTTP Authorization header

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MediaCodec Stream Changes

Pre-4.4 KitKat there is a bug in MediaCodec ACodec.cpp that causes an native assertion when there is a stream change that causes internal port reconfiguration. One such change is a resolution change ie in H.264 SPS/PPS parameters.

This means the MediaCodec object needs to undergo teardown and re-setup, ie

mCodec.stop mCodec.release mCodec = MediaCodec.createDecoderBy... mCodec.configure mCodec.start

The trigger for this is to know when a resolution change is going to happen in the stream before the ES buffer is queued to the input. Therefore, the H.264 ES data needs to pre-parsed to examine SPS/PPS to detect the resolution change.

If the input is actually TS or PES then first parsing for start unit indicator will make this more efficient. Even better is if you know the beginning of the GOP.

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Troubleshooting MediaCodec Output Buffers

A client retrieves a decoded output frame by calling MediaCodec.html.dequeueOutputBuffer. However, the ByteBuffer referred to may be null, empty or in a chipset-specific output format (see Andy McFadden's answer here).

So what if you need to examine the bytes of the decompressed frame, i.e. for a unit test? The answer lies in Andy McFadden's EncodecDecodeTest.java.

The frame needs to be rendered to a Surface (via MediaCodec.releaseOutputBuffer).

Read pixel values using GLES20.glReadPixels

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Asserts in MediaExtractor

These asserts in production code are driving me crazy, had to write my own TS demuxer.

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Parallel build jobs with NDK

ndk-build -j

The -j parameter also takes a integer value for the number parallel jobs if you don't want to saturate all your cores at once.

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Low-latency with MediaCodec

Wrestling with MediaCodec to get good low-latency performance: http://stackoverflow.com/q/21440820/783051