If you haven’t heard of the Android Support Annotations library yet, you’re missing out on a neat new package that will help you catch bugs in your apps. Included in the library is a number of Java annotations, that will help Android Studio check your code for possible errors and report them to you. There are quite a few of them, so I only plan to go over a few of them here, but you should definitely check out the docs for more info about the rest.

@NonNull / @Nullable

@NonNull and @Nullable are probably the most basic of the support annotations, but also some of the most helpful! Annotate a parameter or method with either of these to denote if the parameter or method’s return value can be null or not, and voila, now Android Studio can give us a nice warning that we’re doing something unsafe.

Turn this:

into this:

Bonus points: We can even take this example one step further with the @CheckResult annotation, to tell us know that the return type of this method is something that we are expected to use, rather than the method having a side effect.

@StringRes / @DrawableRes / etc.

Have you ever attempted to call setText on a TextView, and gotten a somewhat mysterious android.content.res.Resources$NotFoundException: String resource ID #0x3039 exception? If you pass an integer to setText, TextView assumes it’s a String resource id, and will look it up in order to set the text. If only there were a way to denote that integers are not valid ids for this method…@StringRes to the rescue!

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public void setText(@StringRes int id) {
  // Do something like getString(id), etc.
}

Now if you try to pass a non-String resource id to this method, you get something like this:

(There are resouce annotations for all resoruce types, @DrawableRes, @ColorRes, @InterpolatorRes, etc.)

@Keep

Today I discovered a new support annotation @Keep. According to the support annotation docs, this annotation hasn’t been hooked up to the Gradle plugin yet¹, but it will let you annotate methods and classes that should be retained when minimizing the app.

If you’ve ever messed around with the cryptic -keep class com.foo.bar { public static <methods> } incantations that you need to use to summon the Proguard Gods, you’ll know how painful it is to rip your hair out, while trying to exclude a particular method or class from being optimized away. This handy annotation will tell Proguard to leave the method or class alone – like so:

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public class Example {
  @Keep
  public void doSomething() {
      // hopefully this method does something
  }
  ...
}

The best part is – if you’re using appcompat-v7, you’re already including support-annotations, so just start using them already!