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Sub folder yields "Package R does not exist"

Using Android Studio. I have one single app Project. com.myapp.app. In this project, I have a sub folder sub - implying a new namespace: com.myapp.app.sub
In this sub folder, all references to R.string.some_string produce the following error:
package R does not exist
How can I make my sub folders aware of the auto-generated R.java file?

This does the trick: Accessing R.java from different packages
Not sure if this is the best solution though.

R.java file gone all of a sudden

I was working on my project and it was fine until recently all of a sudden it went missing when I tried to run the project.This file is auto generated so why did this happen.
In my error log I am getting this error.
"Warning: Ignoring name conflict in resource file for name menu_settings"
Please help me out here.Thanks in advance.

R.java is autogenerated at compile time. If any error in the res folder occurs it can not be genarated. So check inside it for issue. You can use also the problems eclipse perspective

This happens if you have error in the xml files under res files, like layouts, string.xml etc.

Check your res folder, check with drawable and .xml files, if u have any error in xml Compiler will not generate R.java file and do this... Project -> Clean

check your resource file there seems some error.thats why your R.java not generating.

Checkout the Res folder specially images name and XML files follow naming convention for draw able.

My R.java file has disappeared, nothing works

After change some resources (Images) manually my R.java file has disappeared. I've tried all, I've read this, this, and a lot of entries, but nothing works for me.
I have revised all my Layouts and resources, but apparently any layout hasn't problems.
Is possible to export all my project and build another? Or without the R.java class I've nothing to do? thanks a lot!
I've solved it! I deleted the last files added and I restarted eclipsed, right now all is working correctly

Have you checked your problems tab for errors within the /res/ folder?
If there is something wrong with any of your resource files then the R file will not be generated.

Look in your Console output. You probably have an illegally named file and have a message similar to --
Invalid file name: must contain only [a-z0-9_.]

How to resolve the issue of android resources

i'm new to android, i'm getting this error. please help me in providing the solution
Thanks in advance.

R cannot be resolved to a variable When we will get this error.
R.java is an automatically generated file to hold all your resources used in project. It will be created under gen folder when you build your project. While building your project it will assign IDs to each resource you used in project and keeps them in their individual classes (drawable, id, layout, etc.) and creates a file R.java, place it in your package.
If anything wrong in your resource files (drawables or xml layouts) it won't generate R.java file.
So please check it once. I too faced same problem previously.

All the resources in Android are referenced by an 'id'. This 'id' is generated automatically in the file 'R.java', which itself is generated in automatically in 'gen' folder, once you build the project.
So, what you have to do is just 'Build your Project'

Build you project and you will get you.package.name.R.java file - and just import it.

I think I saw the problem. You are having 2 folders named 'res'.
Just delete the res folder which is empty and Clean, build the project

if your gen folder is still missing then check whether you have done installation properly and then check if you have any error on any of the xml files in your project
refer following links
R cannot be resolved - Android error
No generated R.java file in my project
No generated R.java file in my project
http://www.joshuakerr.com/2009/10/23/android-and-the-missing-gen-folder/

Cannot create R.java b/c project has errors...errors result from lack of R.java

edit: This is an Android project. My problem arose when I added a new .wav file to my 'raw' folder.
I seem to have gotten into an endless loop in Eclipse. I deleted my R.java file from my project. Choosing to "Clean" or "Build Project" has no effect (i.e. doesn't generate an R.java file, or put anything into the 'gen' folder, or create any .class files in the 'assets' folder).
I don't have the wrong package name in any of my classes or in my manifest.
I don't have any errors in any of my .xml files.
Every reference to 'R' in my classes are marked as errors, because the R.java file does not exist.
What can I do??

Try deleting the wav file first. If it doesn't fix your problem, look under problems tab and it will give you a direction on what to do. A wav file under res/ shouldn't produce any problems, just make sure its name is valid in Java (don't use -, for example).

I solved this problem creating a blank project and copying the folder "gen" from this project to others projects. After that I rebuilt all projects and Eclipse automatically replaced the R.java file.

if you rebuild it is there any error message on the console? or are you using capital letters or other special characters in your wav file?

Another issue I noticed, it seems that after closing and re-opening eclipse with a slightly invalid XML file, the XML was no longer recognised as having an error, but R.java refused to be generated correctly.
The offending XML attribute was:
<RelativeLayout ...
android:layout_alignRight="+id/">
In hindsight, I had been intending to complete this with a valid id but I exited the program before I had finished. Eclipse did not pick up the error when I restarted later, except to generate an invalid R.java with a missing VariableDeclaratorId (and no indication as to what caused it).