Android Project R,java file cannot be updated automatically, after clean, R.java disappears

Today, an Android project, a new jump page, add the background map, found that there is a r.id can not find, so clean a bit, this problem, found everywhere the r.id can not find, error. It turns out R.java's gone.
Then various Baidu results:
There are said to be re-clean, there is said that Android Tools--fix project Propertities, but none of the work. Then continue to Baidu, see a common point of view is that as long as the XML file has a problem, the system will never automatically generate R.java for you.

See this error to realize, my background image name has a problem, the name can only be the number of letters and underscores, my picture is the middle crossbar, I changed the name of the picture, sure enough, R.java file automatically appeared, and automatically updated, the problem is resolved satisfactorily.

To summarize this type of problem resolution steps:

1.project-->clean;

Fix Project Propertities 2.Android Tools

3. Continue to Clean view background prompt error, generally because of problems in the XML file (such as: ID duplicate ah, or the name of the ID can not find, etc.), there is the file name is not correct, the file name only number + letter + underscore.

Android Project R,java file cannot be updated automatically, after clean, R.java disappears