I fixed the problem. I used the workspace which was given by a python professor. I guess some sets do not match. After changing workspace, it works. Thank all you guys answer.
When i create a new android project, i ask eclipse create the activity for me. the code need to be imported v7, but there is not v7 in the lib. The error message shows up and stop the creating process. Anyone know how to fix it?(And i want to fix it in one time. i dont want it show up every time i create new project)(also if i cant fix it, eclipse cannot finish creating process,it means there are some unknown file have not be created before the error.this is the biggest problem)
[2014-11-26 23:39:54 - s] C:\EclipseWorkspaces\personal\s\res\values\styles.xml:7: error: Error retrieving parent for item: No resource found that matches the given name 'Theme.AppCompat.Light'.
[2014-11-26 23:39:54 - s]
[2014-11-26 23:39:54 - s] C:\EclipseWorkspaces\personal\s\res\values-v11\styles.xml:7: error: Error retrieving parent for item: No resource found that matches the given name 'Theme.AppCompat.Light'.
[2014-11-26 23:39:54 - s]
[2014-11-26 23:39:54 - s] C:\EclipseWorkspaces\personal\s\res\values-v14\styles.xml:8: error: Error retrieving parent for item: No resource found that matches the given name 'Theme.AppCompat.Light.DarkActionBar'.
[2014-11-26 23:39:54 - s]
[2014-11-26 23:39:54 - s] C:\EclipseWorkspaces\personal\s\res\values\styles.xml:7: error: Error retrieving parent for item: No resource found that matches the given name 'Theme.AppCompat.Light'.
[2014-11-26 23:39:54 - s]
[2014-11-26 23:39:54 - s] C:\EclipseWorkspaces\personal\s\res\values-v11\styles.xml:7: error: Error retrieving parent for item: No resource found that matches the given name 'Theme.AppCompat.Light'.
[2014-11-26 23:39:54 - s]
[2014-11-26 23:39:54 - s] C:\EclipseWorkspaces\personal\s\res\values-v14\styles.xml:8: error: Error retrieving parent for item: No resource found that matches the given name 'Theme.AppCompat.Light.DarkActionBar'.
[2014-11-26 23:39:54 - s]