Possible Duplicate:
R cannot be resolved - Android error
I am having a issue which I have had before and I don't understand the cause. My project and code is fine as it was running yesterday. I have open Eclipse today and the whole project looks like it contains errors.
I believe it is some sort of build path issue. I don't understand why it randomly occurs? But in the code where there is R.Layout.LayoutName there is an issue... can anyone help?
I have tried cleaning and building it, I have tried importing android.R but I didn't have this before, it then gives and error and says the layout file doesn't exist.
Are you targeting the android.R or the one in your own project?
Are you sure your own R.java file is generated? Mistakes in your xml views could cause the R.java not to be generated. Go through your view files and make sure all the xml is right!
I think I found another solution to this question.
Go to Project > Properties > Java Build Path > tab [Order and Export] > Tick Android Version Checkbox
Then if your workspace does not build automatically…
Properties again > Build Project
I've fixed the problem in my case very easy:
go to Build- Path->Configure Build Path->Order and Export and ensure that <project name>/gen folder is above <project name>/src
After fixing the order the error disappears.
check your R directory ...sometimes if a file name is not all lower case and has special characters you can get this error. Im using eclipse and it only accepts file names a-z0-9_.
You want Clean Project
Like this
click on
Projects>Clean>select your project
this will help to u
Agree it is probably due to a problem in resources that is preventing build of R.Java in gen. In my case a cut n paste had given a duplicate app name in string. Sort the fault, delete gen directory and clean.
Fought the same problem for about an hour. I finally realized that I was referencing some image files in an xml file that I did not yet have in my R.drawable folder. As soon as I copied the files into the folder, the problem went away. You need to make sure you have all the necessary files present.
Save all layouts, and replace them from the previous version. Start to copy one by one and clean the project everytime, sometimes one of the layouts has something, that eclipse doesn't like. It worked for me.
来源：https://stackoverflow.com/questions/4932282/android-r-cannot-be-resolved-to-a-variable