How to retrieve missing R packages (files) in Eclipse Project (project)

I think a lot of people will meet with me the same problem, but in a short period of time do not know how to be good, can only scratching "manic"!

Now CSDN is one of my notebooks and I will enumerate the meanings of the various issues I have encountered in my project:

But can not write their own items deleted, and then re-establish it! (If SVN is used, it may be easier to re-click) but I want a more convenient way:

Under normal circumstances:

Method One: Select the item "clean"

Method Two: Select the project "Android Tools" Fix

If not, there is another way:

First: Enter your Xxx.xml file, first find the error. Correct the wrong! < after you've changed, your project will be fine >

If it doesn't work,

Second: Change the xxx.xml files in your own project! Then save it and it's OK.