As you build your app’s GUI and add resources (such as string
s in the strings.xml
file or views in the activity_main.xml
file) to your app, the IDE generates a class named R that contains nested classes representing each type of resource in your project’s res
folder. You can find this class in your project’s gen folder, which contains generated source-code files. The nested classes are declared static
, so that you can access them in your code with R.
ClassName. Within class R
’s nested classes, the IDE creates static final int
constants that enable you to refer to your app’s resources programmatically from your code (as we’ll discuss momentarily). Some of the nested classes in class R
include:
• class drawable—contains constants for any drawable
items, such as images, that you put in the various drawable
folders in your app’s res
folder
• class id—contains constants for the views in your XML layout files
• class layout—contains constants that represent each layout file in your project (such as, activity_main.xml
)
• class string—contains constants for each String
in the strings.xml
file.