Android R file can't generate

I engaged a wired problem that the R file can't be generated by eclipse even I clean the project a few time. What happened was I broke the project and also the git file so I clone the project from my bitbucket. When I added the git repos and imported the projects, I found the tricky problem.

After googling a while, I hadn't found right solution. After all, I tried my luck by

switching the android SDK version for the project - because for unknown reason the current sdk version is not working for the project.

and it works. I switched it from 4.0.3 to 4.0.0 and right after the eclipse started building the R file. And then I switched it back to 4.0.3 and it seemed back to normal but once I cleaned the project it failed to generate R file again. So I had to stick with 4.0.0. Strange!

Git+Dropbox always dirty

Solve this issue by just simply set the
filemode = false
for the config of git.

If you are using eclipse+EGit

Go
->GitRepositoryView->Find your Git project->Working Directory->.git->config
You won't miss it.