What is the meaning of such lines like xmlns:app="http://schemas.android.com/apk/res-auto" in android xml file?

Question

xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"

Answer 1

When you want to import attributes in AndroidManifest.xml you have to kind of import their libraries. which you can then access by their prefixs {android:,tools:,app:} Example of of usage are

android:name="yourpackege.App"

tools:overrideLibrary="yourpackege.App"

app:showAsAction="never"

In the above examples attributes being

android:name, tools:overrideLibrary, app:showAsAction

Of course every single prefix has many more attributes for example

android:name,android:theme,android:value

Kindly note though that

The app namespace is not specific to a library, but it is used for all attributes defined in your app readhere

Just to test the explanation above if you remove lets say xmlns:android="http://schemas.android.com/apk/res/android" and rebuild your android application, you will get and error that looks something like