Android Resources

Your Android project is now a basic "Hello World" app that contains some default files. Take a moment to review the most important of these:

app/src/main/res/layout/activity_my.xml

This XML layout file is for the activity you added when you created the project with Android Studio. Following the New Project workflow, Android Studio presents this file with both a text view and a preview of the screen UI. The file contains some default interface elements from the material design library, including the app bar and a floating action button. It also includes a separate layout file with the main content.

app/src/main/res/layout/content_my.xml

This XML layout file resides in activity_my.xml, and contains some settings and a TextView element that displays the message, "Hello world!".

app/src/main/java/com.mycompany.myfirstapp/MyActivity.java

A tab for this file appears in Android Studio when the New Project workflow finishes. When you select the file you see the class definition for the activity you created. When you build and run the app, the Activity class starts the activity and loads the layout file that says "Hello World!"

app/src/main/AndroidManifest.xml

The manifest file describes the fundamental characteristics of the app and defines each of its components. You'll revisit this file as you follow these lessons and add more components to your app.

app/build.gradle

Android Studio uses Gradle to compile and build your app. There is a build.gradle file for each module of your project, as well as abuild.gradle file for the entire project. Usually, you're only interested in the build.gradle file for the module, in this case the app or application module. This is where your app's build dependencies are set, including the defaultConfig settings:

·         compiledSdkVersion is the platform version against which you will compile your app. By default, this is set to the latest version of Android available in your SDK. (It should be Android 4.1 or greater; if you don't have such a version available, you must install one using the SDK Manager.) You can still build your app to support older versions, but setting this to the latest version allows you to enable new features and optimize your app for a great user experience on the latest devices.

·         applicationId is the fully qualified package name for your application that you specified during the New Project workflow.

·         minSdkVersion is the Minimum SDK version you specified during the New Project workflow. This is the earliest version of the Android SDK that your app supports.

·         targetSdkVersion indicates the highest version of Android with which you have tested your application. As new versions of Android become available, you should test your app on the new version and update this value to match the latest API level and thereby take advantage of new platform features. For more information, read Supporting Different Platform Versions.

See Building Your Project with Gradle for more information about Gradle.

Note also the /res subdirectories that contain the resources for your application:

drawable-<density>/

Directories for drawable resources, other than launcher icons, designed for various densities.

layout/

Directory for files that define your app's user interface like activity_my.xml, discussed above, which describes a basic layout for the MyActivityclass.

menu/

Directory for files that define your app's menu items.

mipmap/

Launcher icons reside in the mipmap/ folder rather than the drawable/ folders. This folder contains the ic_launcher.png image that appears when you run the default app.

values/

Directory for other XML files that contain a collection of resources, such as string and color definitions.