Android library project uses declare-styleable -- how to compile?

Question

I have a custom preferences control that I have defined a few attributes for in values/attrs.xml. Just to focus the conversation, here is an example of attributes that could be found in values/attrs.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="MyCustomView">
        <attr name="android:text"/>
        <attr name="android:textColor"/>            
        <attr name="extraInformation" format="string" />
    </declare-styleable>
</resources>

To use the attributes, you use an xmlns tag where you want to use it, and it looks something like this:

xmlns:custom="http://schemas.android.com/apk/res/com.conundrum.app.lib"

Herein lies the problem: the xmlns definition refers to the LIBRARY's package name, and this resource compiles fine in the LIBRARY project. However, the Android project that includes the Library project has a different package name and Android tries to merge all the resources. When it gets to this xmlns definition, it balks because the package name is different in the including Android project.

Anybody got any ideas for using xmlns references in Library projects that are still valid in including Android projects?

Were declare-styleables just an oversight by the Android team when they considered libraries?

Answer 1

I actually played a lot with styleable and libraries and have the following observations:

Imagine that you have a project that has main project and included library:

main
   |--- library

• there is no problem with compiling an application with included library even when the library contains styleable. You can for example include one of my libraries ( http://code.google.com/p/tree-view-list-android/ ). You will find a number of styleable attributes there (like collapsible) and some XMLs using it inside the library.. All compiles and works well whether you compile library alone or as included library... So here it looks good.....
• now, you might experience strange problems with compilation of the main project when you have resources with the same name in both - library and main project. I initially did not understood it, but now I know how it works. For example if you have in your library main.xml which has android:id="@+id/some_id" and then in your main project you have another main.xml (without some_id id), then the R.id.some_id will be generated when you compile the library, but will NOT be generated in the main project - this might lead to compilation errors of the main project because included library .java files most likely will use R.id.some_id (which will be missing). I initially misunderstood the problem and tried to get id dynamically, but it was not needed at the end - it was enough to make sure your layout xmls in library use some kind of privateish namespace.
• and now the most interesting part - how to refer to the styleable parameters in layout.xmls of the project? As you noticed, the following won't work: xmlns:custom="http://schemas.android.com/apk/res/YOUR_LIBRARY_PACKAGE" Surprisingly what works instead is xmlns:custom="http://schemas.android.com/apk/res/YOUR_MAIN_APP_PACKAGE" (!) It indeed looks like an overlook from android team, but once you know it, it works flawlessly.

Answer 2

Use http://schemas.android.com/apk/res-auto

I found this solution given casually as a side-note in the AndroidSVG project:

Aside: Note the special schema URL in the namespace. If you were using a custom View from your own project you would use a URL based on your package name. For example http://schemas.android.com/apk/res/com.example.customview. But since the custom View is in an included library you should use the res-auto short-cut. The real schema URL will be automatically inserted when your app is built.

(I fixed a typo - missing /res/ subfolder - in the quoted text above)