App development today favors small apps rather than large ones. This supports popular trends, like entry-level devices and the “internet of things”. Furthermore, smaller apps download, install and run faster, which is important for your business. This chapter will help you keep your apps as small as possible.
In this chapter, you’ll learn how to prepare a build for release. You’ll learn about the optimizations that ProGuard performs and how to translate to a certain level of obfuscation. This adds a minimal layer of security to help prevent reverse engineering or tampering with your app.
In the process, you’ll learn:
How to use APK Analyzer.
How to leverage optimization rules.
How to fix compile and runtime errors.
Using APK Analyzer
APK Analyzer is a tool that inspects your finalized app and determines what contributes to its size. It presents a breakdown of your app’s files. You can see what takes up the most space, along with the total method and reference counts.
Launch the analyzer by selecting Build ▸ Analyze APK, which opens a dialog for your file system. If it isn’t already selected, navigate to your debug folder and select app-debug.apk. Click OK to open APK Analyzer.
Figure 20.1 — Using APK Analyzer
Note the file size of the current APK. You’ll use this tool again later in the chapter to see the result of your changes.
Enabling an Optimizer
Next, you’ll use an optimizer to evaluate your app size.
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ProGuard Versus R8
Android Studio comes with an optimizer by default: R8. ProGuard was the de facto tool for Android for a long time, while R8 is the newer Google alternative. They’re compatible with each other and perform similar operations to optimize Java bytecode. Both remove unused code, such as methods, fields and classes, and attempt to optimize code for performance.
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Fixing Compilation Errors
As optimizers do their work, they often mistakenly obfuscate and remove code that they think you’re not using — even when you are. Therefore, as you go along, you’ll need to test that everything still works with ProGuard enabled. The earlier you find problems in the build, the easier it will be to fix them. :]
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Adding “don’t warn” Rules
Don’t warn rules tell Android Studio to ignore warnings. This is dangerous, but if you know for sure that you’re not using part of the code, it can come in handy.
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Enabling More Optimizations
At this point, you’ve successfully applied optimizations for your app. However, there are a few more steps you can take for your release version.
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As long as you’ve set minifyEnabled in the optimizer, you can enable the resource shrinker, which removes unused resources after the code shrinker does its job. It will also remove resources in libraries that you include. To make sure it knows which resources your app uses, remove unused library code to make the resources in the library unreferenced.
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If you’ve been working with NDK, you’ll have an Android.mk file under the project’s jni directory. This file tells the compiler how it should optimize native code. Changing the option is as simple as appending a line in the file, as follows:
SOBIP_RQWUVQ := -E1
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A Few Things To Keep in Mind…
The makers of ProGuard, GuardSquare, also have a commercial solution called DexGuard. It minimizes code, but offers more protection regarding its side effect of obfuscation. DexGuard encrypts the classes and strings as well as assets and resource files. It also provides app and device integrity checking, which is important to keep spammers out of your app.
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Key Points
R8 is the default code shrinker and minification tool in Android.
Don’t warn rules ignore warnings and errors.
Keep rules allow you to keep the optimizer from touching specific code.
Instead of keeping entire classes or large parts of code, keep only the minimum code you need, giving you better optimizations.
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