什么是sender.selected =！sender.isSelected实际上是为了让我的按钮切换？

Currently learning objetive-c. Gone through various books and also some tutorials on the lynda website and have now found the Stanford course which I think suits my style of learning. I've been watching the first 3 lectures over and over again basically doing it until I'm 100% with what has been taught and I'm not far.Currently learning objetive-c. Gone through var