问题
I changed the dependent projects of one of my project and moved one of my files there as an experiment. I now moved it back but the project won't run. It tells me I have an error even though I can't see one and "Clean project" doesn't help. However, the project has an exclamation mark next to it. What does that mean?
回答1:
Check Errors window. My first idea would be that no build target is set. Right click the Project, select Android and make sure that a Build Target is checked. Sometimes you need to uncheck it, select a different API, apply settings, and then again select the API that was originally selected.
来源：https://stackoverflow.com/questions/5895860/android-eclipse-exclamation-mark-next-to-project-name