Cannot override library's xml resource with png resource in application?

Question

I have an Android library MyLib containing everything I need for my app (targeting Android 2.2). This library has an XML resource:

drawable/main_background.xml

In my Application MyApp project I reference MyLib. Here I want to override specific resources (i.e. branding). So I added a background image in MyApp:

drawable/main_background.png

Eclipse keeps giving me this error:

[com.mycom.mylib.myapp] res\drawable\main_background.xml:0: error: Resource entry main_background is already defined.
[com.mycom.mylib.myapp] res\drawable\main_background.png:0: Originally defined here.

How can I override the resource in the library project?

Answer 1

You cannot simply override resource ID (it's the resource ID you are overriding, not the actual file) with a file with different extension in Android SDK. However, you can do the trick by putting in your project xml file with the same name (main_background.xml) and fill it in a proper way to display your new file (main_background.png), which you need to rename earlier. All syntax you need is descibed here:

http://developer.android.com/guide/topics/resources/drawable-resource.html

, in your case it could be simply (assuming you put this in your non-library project as main_background.xml, and you have your new png as main_background_new.png):

<?xml version="1.0" encoding="utf-8"?>
<bitmap
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:src="@drawable/main_background_new" />

With above solution, you could refer to @drawable/main_background from your project and it should use your file included with that project, instead of a library one.

Answer 2

[com.mycom.mylib.myapp] res\drawable\main_background.xml:0: error: Resource entry main_background is already defined.
[com.mycom.mylib.myapp] res\drawable\main_background.png:0: Originally defined here.

I don't believe you can have the same file name even with different extensions. Try naming the png something else.

Now, i've not used overriding, So this seems odd as you'd expect this to be how you override the asset. However i think you've either got the two assets in your lib named the same. And that in your project it might be ok to have an asset with the same name. I would however check that its ok to have different types. XML is different than png, and if you access the asset from code you could get type errors.

Let me clarify the above point. I understand that a library project can have an item with the same Resource ID as an item in your application.

However the error above suggests that both main_background.png and main_background.xml are in the same project ([com.mycom.mylib.myapp]) which i don't believe is correct.

Further reading

This page describes the various types of project including the library project http://developer.android.com/tools/projects/index.html

Now i don't know where i got the impression from but having looked again it simply doesn't state anywhere that you can override a resource by using the same resource name. God knows why i thought that was a feature.

So no, the same rule applies as far as i can tell, that resources have to be named uniquely even across library projects, otherwise the generated resource ids will conflict. (The error your getting)

What is explained is how resource conflicts are managed.

Resource conflicts Since the tools merge the resources of a library project with those of a dependent application project, a given resource ID might be defined in both projects. In this case, the tools select the resource from the application, or the library with highest priority, and discard the other resource. As you develop your applications, be aware that common resource IDs are likely to be defined in more than one project and will be merged, with the resource from the application or highest-priority library taking precedence.

The system will use the resource with the highest priority, discarding everything else. Whats odd, is that you would think that a compile error wouldn't occur as the compiler should be discarding the resource. This makes me believe that the original poster had the similarly named assets in the same project, and not across the lib and project.

I haven't read anywhere that this is actually an intended feature. Got any links to say otherwise? (comment them)