在Eclipse ADT来开发Android App时会遇到以下问题：
"myproject/gen already exists but is not a source folder. Convert to a source folder or rename it"

解决办法是：

1.Right click on the project and go to "Properties"

2.Select "Java Build Path" on the left

3.Open "Source" tab

4.Click "Add Folder..." and check "gen" and "src"

Reference

1.

http://stackoverflow.com/questions/9532045/gen-already-exists-but-is-not-a-source-folder

Eclipse.Error.gen already exists but is not a source folder.