The android package in eclipse cannot be introduced. (The SDK of other versions is newly developed)

This is a simple problem. Do not try it!

I did not touch my computer yesterday. I opened eclipse tonight and found that all android projects were wrong. I checked that it was a problem with the introduction of all android packages. This was a hard nut to crack. I just got started with Android, Baidu, I haven't found any forums for a long time. Switch off eclipse and think about it for a while. Let yourself calm down and open eclipse again. Think about the SDK problem, because sdk2.2 was downloaded the day before (I used 4.2, next is the latest, cainiao, Do not spray), resulting in the SDK not introduced, a check, it is indeed like this, and then re-launch an ADT plug-in, okay! Although it's a trivial matter, I'm still very happy!