What does "android.R.id.content" mean?

Explanation: The android.R.id.content is a constant that has the value of a Integer, which is the address referenced to such content, which is declared in R.java which is a file that is generated every time you build in the project.

Explanation of content itself:

android.R.id.content - is an integer used to reference or identify the element used as the basis of your View .

Each element you create will have an address for it in R.java , this android.R.id.content is just an easier way to reference your element.

android.R.layout.nomedolayout is also used to reference XML Layouts in your application.

They are Resources of your application, so they are in the res folder of your project Just like there are others:

android.R.strings.nomedastring - for strings entered in res/values/strings.xml android.R.color.nomedacor - for colors registered in res/values/colors.xml android.R.attr.nomedoatributo - for attributes declared in res/values/attrs.xml android.R.style.nomedoestilo - for styles that are in res/values/styles.xml

Details:

Strings are used to reuse the same string for multiple places, or to change only one place when you want to change a pattern, such as a title that is used in all% s of your project, you you want to change it and not have to change at all Activity 's you use a string in Layout and then just change it in Layout

Color's has the same goal as the strings but would, in this case, color.

Attr's are attributes, but consist of the same goal.

Styles are used to create themes and modify standard Android styles for Android components.

These properties are used in the Visual of your Strings.xml , that is, Activity .

Note: Layouts are in Layout .

This is the root view value. "android." is not used to reference resources of the app itself. For your own resources , use only R. , not android.R .

The android.R.id.content is a generic identifier for the root element of the view.