Q:

Why AndroidStudio shows warning "Namespace declaration is never used"?

This is my layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal" >
</LinearLayout>

Taked from the android official training
In the second line, AndroidStudio shows this warning:
Namespace declaration is never used

Why this happens?
Thank you.

A:

This is because you don't have anything with tools namespace actually declared in your xml.
Look at the android namespace, you have 3 elements with that namespace, but none for tools.
The namespace tools (http://schemas.android.com/tools) is used for the GUI designer and is not used for running apps on Android devices so you can safely remove it.

