In Android Applications What Is The Role of "R.Java"

In Android applications what is the role of R.java?

Every application uses resources such as strings, drawbles, layouts, and styles. Instead of hard coding such resources into an application, one externalizes them and refers to them by ID. The R.java file contains all those resource IDs, whether assigned by the programmer or generated by the sdk.

What is the concept behind R.java?

android.R.java is not just where XML ids are stored. It also contains access to resources - such as drawables, layouts, strings, arrays, and basically anything you can declare in resources.

Personally I find that it is useful when using Eclipse. I can simply type findViewById(R.id. and Eclipse will show a tooltip with a list of options to choose from.

However at a platform level, I would say that the hardcoded id variables help prevent errors when using Strings to identify resources -- something that can be debuggable while programming (or during compilation, rather than runtime).

What is the class R in Android?

R is a class containing the definitions for all resources of a particular application package. It is in the namespace of the application package.

For example, if you say in your manifest your package name is com.foo.bar, an R class is generated with the symbols of all your resources in com.foo.bar.R.

There are generally two R classes you will deal with

1. The framework resources in android.R and
2. Your own, in your namespace

It is named R because that stands for Resources, and there is no point in making people type something longer, especially since it is common to end up with fairly long symbol names after it, that can cause a fair amount of line wrapper.

what R.java file actually does and how

"Acts as some pointer to other files" is actually absolutely correct, now the question is which files it points to how it is done.

What does it contain?

R file contains IDs for all the resources in the res folder of your project and also some additional IDs that you define on your own (in the layouts, for example). The IDs are needed for the Android resource management system to retrieve the files from the APK. Each ID is basically a number which corresponds to some resource in the resource management system.

The file itself is needed so you can access or reference the resource from code by giving the ID of the resource to the resource manager. Say, if you want to set the view in the activity, you call

setContentView(R.layout.main);

main in the R file contains the number which is understood by the Android resource management system as the layout file which is called main.

Why is it better than just plain file names?

It's harder to make a mistake with the generated fields. If you write the field name incorrectly, your program won't compile and you will know that there's an error immediately. If you write an incorrect string, however, the application won't fail until it is launched.

If you want to read more on this topic, you should check the Android documentation, especially the Accessing Resources part.

Understand the R class in Android

R.java is the dynamically generated class, created during build process to dynamically identify all assets (from strings to android widgets to layouts), for usage in java classes in Android app. Note this R.java is Android specific (though you may be able to duplicate it for other platforms, its very convenient), so it doesn't have much to do with Java language constructs. Take a look here, for more details.

What is the difference between R. java and resources?

Android R.java is an auto-generated file by aapt (Android Asset Packaging Tool) that contains resource IDs for all the resources of res/ directory.

so if you add an image to your drawable file it will generate an ID in R.java file

the R.java file in android studio 3.4

Try this:

\app\build\generated\not_namespaced_r_class_sources\debug\processDebugResources\r\<package_name_tree>\R.java

package_name_tree means : If package is a.b.c
the goto: /a/b/c/R.java

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