确定支持库的最低版本

Question

When I want to create an Android app that can use the recent supported features of Android, I use libraries like:

appcompat_v7
support_v4

What I haven't been able to determine is what is the earliest version of Android that an appcompat_xxx or support library can actually support. Where do I find this information?

Answer 1

It's all in the name - appcompat_v7 supports API 7 and later, support_v4 supports API 4 and later.

It's also clearly stated in the docs for each library, for example:

This library is designed to be used with Android 1.6 (API level 4) and higher.

http://developer.android.com/tools/support-library/features.html#v4

Also, although this isn't always required, you should try to match up your targetSdkVersion with the respective version of the library. For example, if your targetSdkVersion is 19, you should use com.android.support:appcompat-v7:19.+

To be clear: the support libraries, as dictated by their name, are designed to support a minimum API level. Meaning - they can be safely used on devices running that API level, as well as devices on any later API level. If you attempt to use appcompat_v7 on a donut device (API level 4), or the leanback-v17 library on a Jellybean 4.1 device (API level 16), your app will likely crash with something like a ClassNotFoundException .

The libraries were originally supposed to provide the functionality of newer API levels to the older API levels, such that you could write nearly the same code and leverage the latest platform paradigms in a single APK that would support old and new devices.

Fragments are a perfect example of this. The Fragment class was introduced with Honeycomb (API level 11). Google then released the support_v4 library which contained a back-ported version of the Fragment class and it's respective APIs. Again, as dictated by it's name , this library could be safely used in an app that supports all the way back to API 4. If you install an app using the v4 library on a API 3 device, it will crash. If you install it on, say, an API 8 device, it will work as intended.

Perhaps you're getting caught up on the seemingly delicate nature of relying on a file name to specify the min sdk version - now this is a bit of a guess, but when the v4 library was first introduced, it was just a .jar file. Meaning, you could add it to your app's classpath, no matter what minSdkVersion you use, and it would compile without complaining. MY guess is that Google wanted to explicitly name these libraries using their minimum SDK version to avoid developers trying to use them in apps that are meant to support early API versions. Aside from their docs, which again very explicitly answer your question, the filename was perhaps was a risk mitigating approach to help developers who don't read the docs.

Fast forward to 2014, many of these libraries either come in the form of .aar files (via Gradle), or you need to import them as projects. This is because these libraries now include resources such as images and themes, which cannot be packaged into a .jar file. An added benefit here is that this allows Google to include an AndroidManifest.xml with the library which specifies a minSdkVersion . At compile time, the build tools' manifest merger will complain if your minSdkVersion is lower than the minSdkVersion specified in any included library projects.