Try-with-resources desugaring support in Android's build tools

During one of the code reviews with my colleague I've noticed he used try-with-resources Java 7's feature. To my then latest knowledge, try-with-resources required minSdkVersion 19 (while our app's minSdkVersion is 16) - which is based on the following statement (see under SDK Tools, Revision 22.6 (March 2014)):

Added support for Java 7 language features like multi-catch, try-with-resources, and the diamond operator. These features require version 19 or higher of the Build Tools. Try-with-resources requires minSdkVersion 19; the rest of the new language features require minSdkVersion 8 or higher.

My colleague told me that neither Lint nor compiler haven't warned about that, which was strange - since I vividly remember they both did in the past. Bug in Lint could explain that, but how did it compile? We decided to review our assumptions.

Verifying 64-bit libraries are being loaded

If you're bundling native libraries inside your Android application, then you've probably already know that starting August 1, 2019, your apps published on Google Play will need to support 64-bit architectures. In this post I'll show how we can explicitly choose the 64-bit ABIs to run, and verify that the 64-bit library was indeed loaded at runtime.

The support 64-bit architectures guide provides a command for selecting which ABI libraries to use during the APK installation process:

# A successful install:
$ adb install --abi armeabi-v7a APK_FILE.apk
Success

This command can be handy when your APK includes several ABI libraries, your CPU able to run multiple ABIs and you want to explicitly specify which ABI to use.

How to manually create Android emulator's internal storage disk image

Built-in AVD Manager incorrectly generates (internal storage) disk images when you're creating new virtual device targeting API 19 or greater.

On API 19 - no matter what size you specify during the virtual device configuration, the maximum that you're going to get is 200mb. On API 21 and 22, the maximum size increased to 550mb. This issue already has appropriate question on StackOverflow and AOSP bug report.

For average application this will be sufficient, but for large application (or when you need to install several application that talk to each other) it can be problematic.

Commons Codec on Android

If your application depends on Commons Codec library (version 1.4 and above), and you are not aware that Android framework already includes this library, then there's a chance that your application will crash with a runtime exception.


Why does the Android framework includes the Commons Codec library?

Android framework shipped with HttpClient (version 4.0 pre-BETA, an ancient 2008 release). HttpClient depends on Commons Codec. Therefore, AOSP had to include Commons Codec as well.


OK, so can I use framework's Commons Codec library in my application?

Unfortunately no. This API is hidden and not exposed in Android SDK for application developers. You can invoke the library's classes using reflection of course, but by doing so you take the risk of relying on undocumented APIs, which is not recommended at all.

Too many methods in main-dex?

Notes:
1. The content of this post is relevant only if your minSdk < 21. On Lollipop, no ClassLoader patching required.
2. This solution worked for me well, but it might not work for you in the same way. So please use it on your own risk. Nevertheless, I would be happy to know of your problems - so please post in comments!


Right after the release of multidex support we removed our custom solutions (for 64k methods problem) in favor of multidex support library. Gradle for Android plugin v0.14.0+ simplified the process even more - it implemented all the manual tasks (I wrote about some of them in my previous post) that we had to do previously.

Lately we encountered another issue: we have reached the 64k methods limit in main dex as well. It comes in form of the following error when we're building our project:

UNEXPECTED TOP-LEVEL EXCEPTION:
com.android.dex.DexException: Too many classes in --main-dex-list, main dex capacity exceeded
  at com.android.dx.command.dexer.Main.processAllFiles(Main.java:494)
  at com.android.dx.command.dexer.Main.runMultiDex(Main.java:332)
  at com.android.dx.command.dexer.Main.run(Main.java:243)
  at com.android.dx.command.dexer.Main.main(Main.java:214)
  at com.android.dx.command.Main.main(Main.java:106)

You can say: man, something is wrong with your design if you're having such a problem!
Well, you are quite right, and we're thinking hard on how to split various features of our application into separate apps. But for short-term, we had to find a solution for this specific issue.

Generating main-dex-list file

[Update - 10/31/2014] Gradle plugin v0.14.0 for Android adds support for Multi-Dex. Everything that is written below is now done automatically. All you need to do is to add this line in your build.gradle file:
android {
   defaultConfig {
      ...
      multiDexEnabled = true
}

In my previous post I described the 65536 methods issue and how to solve it using multi-dex technique. In overall, this solution is pretty straightforward - you tell dx to operate in multi-dex mode, and add the multi-dex support library to patch the ClassLoader on application start-up.

The only tricky part is the main-dex-list file that specifies all the classes that you want to be included in the main dex file. dx takes this file as a parameter and generates appropriate dex files.

Failing to keep required classes in the main dex file will produce the following runtime exception:

java.lang.RuntimeException: Unable to instantiate application info.osom.multidex2.Application: java.lang.ClassNotFoundException: Didn't find class "info.osom.multidex2.Application" on path: DexPathList[[zip file "/data/app/info.osom.multidex2-1.apk"],nativeLibraryDirectories=[/data/app-lib/info.osom.multidex2-1, /vendor/lib, /system/lib]]
            ..
     Caused by: java.lang.ClassNotFoundException: Didn't find class "info.osom.multidex2.Application" on path: DexPathList[[zip file "/data/app/info.osom.multidex2-1.apk"],nativeLibraryDirectories=[/data/app-lib/info.osom.multidex2-1, /vendor/lib, /system/lib]]
            at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
            at java.lang.ClassLoader.loadClass(ClassLoader.java:497)
            at java.lang.ClassLoader.loadClass(ClassLoader.java:457)

Now, you may ask, which exact classes should be included in main dex file? And if I have many classes, do I need to write all those class names by hand?

Multi-dex to rescue from the infamous 65536 methods limit

You landed on this page because you've probably received the following stack trace when you tried to build your Android project:

UNEXPECTED TOP-LEVEL EXCEPTION:
java.lang.IllegalArgumentException: method ID not in [0, 0xffff]: 65536
at com.android.dx.merge.DexMerger$6.updateIndex(DexMerger.java:501)
at com.android.dx.merge.DexMerger$IdMerger.mergeSorted(DexMerger.java:282)
at com.android.dx.merge.DexMerger.mergeMethodIds(DexMerger.java:490)
at com.android.dx.merge.DexMerger.mergeDexes(DexMerger.java:167)
at com.android.dx.merge.DexMerger.merge(DexMerger.java:188)
at com.android.dx.command.dexer.Main.mergeLibraryDexBuffers(Main.java:439)
at com.android.dx.command.dexer.Main.runMonoDex(Main.java:287)
at com.android.dx.command.dexer.Main.run(Main.java:230)
at com.android.dx.command.dexer.Main.main(Main.java:199)
at com.android.dx.command.Main.main(Main.java:103)

or this stack trace if you're using dx version 1.8 (shipped with SDK build tools 19.0 and above):

trouble writing output: Too many method references: [num of methods]; max is 65536.
You may try using --multi-dex option.

If this is the first time you see this message, then you'll be surprised to know that Dalvik bytecode has a fundamental limitation which allows to invoke a maximum of 2^16 (65536) methods (per dex file). One glance on a list of StackOverflow questions on this topic is enough to realize how painful this limitation for us.