Hmm, before committing my project to Mercurial source control I like to run a clean so that nothing that’s part of a build shows up as a change that I don’t want to commit (although I’ve added lines to .hgignore to ignore any generated class files and the gen directory where the ADT auto generates some files  so this probably wasn’t even necessary).

When I came back to my project at a later date there were errors in all of my activity classes, turns out that the auto generated R.java file had been deleted and was stubbornly refusing to be re-generated and so anything that depended on this (lots of stuff!) had errors, really f**king annoying.

I never found a satisfactory solution to this problem and eventually restarted the project from scratch as I’d only really just started it anyway, Google gave me few suggestions from other people but none of them worked, it seems a lot of people have had this issue. Here are some of the popular suggestions that have worked for other people.

  • Clean/rebuild – These options are under the ‘project’ menu in the main Eclipse menu, usually the project is set to build automatically whenever changes are saved so after a clean a build is usually performed, if it’s not the clean dialogue gives you the option to build immediately after a clean.
  • Deleting gen – This should cause gen and everything under it to be re-generated, the directory itself and BuildConfig.java were re-generated for me but not R.java.
  • Setting derived to false on gen – You can check this by right clicking on the file in Eclipse and selecting properties, apparently if you put gen under source control when it’s pulled out it can have the derived property set, as I didn’t have gen under source control this was never the case for me.
  • Restart Eclipse.

So far everything has been fine since, perhaps I’d missed out a file that should have been under source control which then got deleted on a Mercurial ‘update’ command? I guess the takeaway lesson for me is to be extremely careful to make sure any changes that should be committed are before updating or pulling code.

Came across this again today and found a fairly comprehensive list of things to try on Stack Overflow here http://stackoverflow.com/questions/2757107/developing-for-android-in-eclipse-r-java-not-generating.

Second answer is most useful I think.

This is an annoying problem that I would come across from time to time.

When debugging a Java application on Linux (Mint 11) using Eclipse, on hitting a breakpoint the whole system would appear to freeze.

I found I could drop down to a shell with CTRL+ALT+F1, login then use list the running processes and grep for any java processes and kill the relevant process.

simon@simon-mint-vm ~ $ps -ely | grep java
S  1000  2374  2373  6  80   0 442072 297255 futex_ ?      00:01:57 java
S  1000  3216  2374  0  80   0 86264 1442616 futex_ ?      00:00:08 java
simon@simon-mint-vm ~ $ kill -9 3216

Then return to the X session with CTRL+ALT+F7 and the screen would be unfrozen.

After having to do this numerous times I managed to find a solution on the internet; when starting the jvm give it the option -Dsun.awt.disablegrab=true

In Eclipse you would enter this in the ‘VM arguments’ pane in the ‘Debug Configrations’ dialogue.

I believe this to be a JVM problem rather than anything to with Eclipse, I was using 1.6.0.26 JRE.