One of the things that's really helpful about themes, is that we can use them to 0:00 make our app look pretty consistent across many different versions of Android. 0:03 We used to have to do this using multiple styles that targeted 0:07 different versions of the SDK. 0:10 But we get a lot of help now by way of the Android support libraries. 0:12 Check out how this is described here, in the Android developer docs. 0:16 You may want a standard way to provide newer features on 0:19 earlier versions of Android, or gracefully fall back to equivalent functionality. 0:22 Rather than building code to handle earlier versions of the platform, 0:26 you can leverage these libraries to provide that compatibility layer. 0:30 So what that's telling us is that, we can plug in this support library to our 0:33 project, and there are some things available for us that make it easy for 0:37 our app to be backwards compatible on older versions of Android. 0:40 That's important because some of those older versions don't have 0:44 some of the newer features that we're using in our app. 0:46 So by default, we are taking advantage of a few compatibility features 0:49 provided by the app components package of the support library. 0:53 If we click on Features over here, 0:56 we can read about some of the common useful components available to us. 0:59 For example, 1:03 this dark gray bar here at the top of our screen is called the App Bar. 1:03 And it wasn't always a part of Android. 1:07 It was first introduced in an older version of Android, 1:09 and it was called the Action Bar. 1:11 And then it was updated and re-named to the App Bar. 1:12 So, some older versions of Android that people are still using, 1:15 don't have an App Bar, or an Action Bar. 1:18 But, it's really useful for 1:20 certain actions and app navigation, which we'll learn more about later. 1:21 But we can include the app bar on older versions of Android, 1:25 by using the appcompat support library. 1:28 Let's take a look at what was created automatically for us. 1:31 So first let's dig into our build.gradle file, 1:34 remember to click on the second one here, the Module app one. 1:36 And down here at the bottom we see a dependency for appcompat. 1:39 So this first part, com.android.support is how we include the support library. 1:45 Then different sections of the support library like appcompat 1:51 are specified after the colon and then the specific version is appended last. 1:54 So this was included automatically for us but if you ever need to add 1:59 a new support library package yourself you can look it up in the developer docs. 2:02 Let's go back and take a look. 2:06 Normally, I would just search for the support library or 2:08 the specific package up here at the top. 2:10 But, we're already at the right page. 2:12 So, if we click on Packages here on the left, 2:14 we now see all the available packages in here on the right. 2:17 If we click on one, like v7 appcompat library we can find the exact 2:20 value that we should use in our Gradle file, here it is down here. 2:25 Note that this will always be the latest version of the support library, 2:29 which you can update by using the STK manager that we briefly explored earlier. 2:33 To do so just come up here back to the STK manager. 2:37 Click on SDK Tools here and then make sure that Android Support Library is checked 2:40 and that it's completely installed and up to date. 2:45 Okay, so this includes the appcompact package and 2:48 that means that we can use its features in code. 2:51 Back in styles.xml, 2:54 we saw there were already extending an AppCompat theme right here. 2:55 Next if we open up mainactivy.java we see that it's extending 3:00 AppCompactActivity instead of a regular activity class. 3:04 Again this is used to make sure that the app bar works on older 3:08 versions of Android. 3:10 This AppCompactActivity provides an app bar and also some material design 3:12 aesthetic changes which makes things look more consistent across versions. 3:16 We'll explore some of the other support library features in future projects 3:20 like a recycle view, but it's important to know what the support library is and 3:23 how to include different packages. 3:27 Remember that its main function is to make your app look and 3:29 work virtually the same on both old and new versions of Android 3:31