Understand the R Class in Android

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 R class in android

Your question is duplicate of Understand the R class in Android

When your application is compiled, aapt generates the R class, which
contains resource IDs for all the resources in your res/ directory.
For each type of resource, there is an R subclass (for example,
R.drawable for all drawable resources) and for each resource of that
type, there is a static integer (for example, R.drawable.icon). This
integer is the resource ID that you can use to retrieve your resource.

I got this detail from the below link ,check this once for more details :
http://developer.android.com/guide/topics/resources/accessing-resources.html

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.

Android studio hides R class

You can find R class by searching it with "shift + cmd + o" or "double shift".

I guess new android studio update directs to the xml source of the resource.

What does R.id.myView refer to?

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

public final class R 
extends Object 

.id - Find view using its id "defined by you"

public static final class R.id 
extends Object 

myView - It is the view that you defined using the android:id="@+id/your_view" attribute in your XML file.

So, finally we can find or identify any view using R.id.your_view.

Meaning of R.layout.activity_main in android development (JAVA language)

R.java is a class (with inner classes, like layout or string) generated during the build process with references to your app's resources. Every resource you create (or which is provided by Android) is referenced by an integer in R, called a resource id.

R.layout.* references any layout resource you have created, usually in /res/layout. So if you created an activity layout called activity_main.xml, you can then use the reference in R.layout.activity_main to access it. Many built-in functionality readily accepts such a resource id, for example setContentView(int layoutResid) which you use during the creation of your activity and where you probably encountered this particular example.

If you create a string resource (in strings.xml) like this:

<string name="app_name">Application name</string>

it will get a new reference in R.string.app_name. You can then use this everywhere where a string resource is accepted, for example the android:label for your application in AndroidManifest.xml, or on a TextView; either in the xml:

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/app_name"
    />

or in code: textview.setText(R.string.app_name).

You can access resources programmatically using the Resources class, to which you can get a reference by calling getResources on any context (like your activity). So for example you can get your app name described above in your activity by calling this.getResources().getString(R.string.app_name).

You can also supply different resources for different device properties/settings (like screen size or language), which you can access using the same references in R. The easiest example here, imho, is strings: if you add a new values folder in /res with a language specifier (so /res/values-nl for Dutch) and you add strings with the same identifier but a different translation and the resource management system cleverly figures out which one to provide for you based on your user's device.

I hope this helps a bit. For more information on resources see the documentation.

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

Why I do not need to import the android R class?

It is because your MainActivity.java are inside the package name which is the same as package name declared in AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="tld.mydomain.buttonclickcounter">

</manifest>

The R.java will be generated based on the package name in AndroidManifest.xml. So, if you're using other package name like tld.mydomain:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="tld.mydomain">

</manifest>

you then need to import the R.java with tld.mydomain.R.

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