Using a non-android namespace prefix in child elements in a layout

Question

I am trying to use custom attributes in some Android layouts, but I am getting an error (from Eclipse) when I try to use a namespace prefix other than android: in a child element. Note that it works ok when I use the custom: namespace prefix in the root/parent element in the file, just not the child element.

For example, here's a simple layout with the custom namespace specified:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:custom="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    custom:my_tag1="whatever">                            <!-- compiles fine -->

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:scaleType="fitCenter"
        custom:my_tag2="true"/>                           <!-- generates an error -->
</LinearLayout>

The error that Eclipse gives (only on the second attempt to use the custom: prefix) is:

Unexpected namespace prefix "custom" found for tag ImageView.

If I make my root element an ImageView instead of a LinearLayout, the prefix is accepted. So it seems to be just a problem using the namespace prefix in a child element.

Also, if I try to add another xmlns:custom="http://schemas.android.com/apk/res-auto" attribute to the ImageView, it complains as well.

If it helps, here is the attrs.xml file I'm using with the above:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <attr name="my_tag1" format="string"/>
    <attr name="my_tag2" format="boolean"/>
</resources>

I've seen some stuff online that leads me to believe what I want to do should be possible. For example, in the accepted answer here, Qberticus uses the prefix "whatever" in a child class. Similarly in the post here.

I don't get it. Is using a non-android namespace prefix just not allowed for child elements, or am I doing something wrong?

Answer 1

It can be ignored, I always did it and I didn't encounter any problems. To make it go away you need to set the following:

1. add xmlns:tools="http://schemas.android.com/tools" to your root view
2. add tools:ignore="MissingPrefix" to your text view

On a side note, however, I usually use custom attributes with custom views :-)