Useful Android system resources

Question

Android comes with lots of system resources (android.R) that can be used to save you time and make your application lighter.

For example, I recently discovered that Android provides localized strings for Yes (android.R.strings.yes), No (android.R.strings.no), Cancel (android.R.strings.cancel) and Ok (android.R.strings.ok), among other strings.

What other system resources do you recommend using? Or is there a reason to avoid using system resources?

Answer 1

You can find a full listing of all system resources in the android package.

Every time I want to do something on Android I check to see if there's a system resource that covers what I want to do. It is helpful to import the Android source code (in particular, their /res/ folder) when searching for already-implemented resources that you might want, so you can see their specific implementation.

Personally, I find myself most often using:

• Built-in Android layouts for standard tasks, such as spinner dropdowns.
• Android ids (android.R.id), because you are often required to use these if you want to use some of Android's widgets (for example, TabHost/TabWidget requires you to use "android:id/tabhost", "android:id/tabs" and "android:id/tabcontent" if you want to implement an XML layout).
• Built-in colors, especially android.R.color.transparent.
• Android's built-in fade-in and fade-out animations in android.R.anim.

Answer 2

As CommonsWare mentioned, you don't have to download the Android source repository to inspect the resources; just go to <android-sdk-dir>/platforms/android-X.X/data/res/. However, if you start using these you will quickly become disappointed to find that most of them are not available through the android.R class. Most of the time I have to import them into my Eclipse workspace anyway. :-(

My favorite resources are the drawables that show differently based on a control's focused/pressed/disabled states (like android.R.drawable.btn_default). I use those or tweak them to create custom buttons for my apps. As you can see if you look at /data/res/drawable/btn_default.xml, they are defined as a <selector> XML element, which gets inflated into a StateListDrawable at runtime. You could also create your own StateListDrawables and they're super useful, both as View backgrounds and as a button's "compound drawable" (see TextView.setCompoundDrawables()).