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28 février 2018

Improving Stability by Reducing Usage of non-SDK Interfaces

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Posted by David Brazdil, Software Engineer

In Android, we're always looking for ways to improve the user and developer experience by making those experiences as stable as possible. In this spirit, we've been working to ensure that apps don't use non-SDK interfaces, since doing so risks crashes for users and emergency rollouts for developers. In Android N, we restricted the set of symbols that C/C++ code could use. This change ensured that apps using C++ rely on stable NDK interfaces rather than incur the incremental crashes caused by reliance on unstable, non-NDK interfaces. Starting in the next release of Android, we will further increase stability by expanding these restrictions to cover the Java language interfaces of the SDK.

What behavior will I see?

Starting in the next release of Android, some non-SDK methods and fields will be restricted so that you cannot access them -- either directly, via reflection, or JNI. If you try, you can see errors such as NoSuchFieldException or NoSuchMethodException.

Initially, this restriction will impact interfaces with low or no usage. It is an explicit goal of our planning and design to respect our developer community and create the absolute minimum of change while addressing app stability issues flagged by our users and device manufacturers. In cases where a migration to SDK methods will be possible but is likely to be technically challenging, we'll allow continued usage until your app is updated to target the latest API level. We plan to broaden these restrictions in future platform versions, giving developers time to migrate with long advance warning, and also giving us time to gather feedback about any needed SDK interfaces. We have always said that using non-SDK interfaces is always risky -- they might change in any release as we refactor code to add features or fix bugs. So if your app currently relies on non-SDK interfaces, you should begin planning a migration to SDK alternatives.

Because the Java language has different features from C++, this restriction will take a slightly different form than the previous symbol restriction. You should not access classes that are not part of our SDK, but you also need to be sure that you are only using the officially documented parts of each class. In particular, this means that you should not plan to access methods or fields that are not listed in the SDK when you interact with a class via semantics such as reflection.

What if there isn't a SDK alternative?

We know that some apps may be using non-SDK interfaces in ways that do not have an SDK alternative. We value your feedback about where and how we need to expand and improve the public APIs for you. If you feel that you'll need the SDK API expanded before you can stop using non-SDK ones, please tell us via our bug tracker. We will be monitoring this list closely and using this valuable feedback to prioritize. It is critical for us to get this feedback in a timely manner so that we can continue to both tune the blacklist to minimize developer impact and also begin developing any needed alternatives for future platforms.

What's coming next?

In the next Android developer preview, you'll be able to run your existing apps and see warnings when you use a non-SDK interface that will be subject to blacklist or greylist in the final release. It's always a best practice to make sure your app runs on the developer preview, but you should pay specific attention to the interface compatibility warnings if you are concerned that you may be impacted.

In conjunction with the next developer preview and the new bug tracker category, we'll be monitoring usage of non-SDK interfaces. In cases where official SDK alternatives already exist, we'll publish official guidance on how to migrate away from commonly used non-SDK interfaces.