I'm trying to download and analyze a few apps from F-Droid.com but when I grab all the java files and all the other files and copy them into my IDE (Motodev Studio for Android) errors pop up all over the place because the R.java file is missing. I can't seem to find the reason why the R.java file is absent and the app (obviously) won't run without it. can anyone help? Here is an example of an app I'm trying to download:
http://f-droid.org/repository/browse/?fdid=arity.calculator&fdpage=2