转自:https://blog.csdn.net/suncherrydream/article/details/17757529 as是用来类型转换的比如:两个类:A和BB b = new B();//使用as,类型不匹配,不会引发异常,会返回一个null,此时 a = nullA a = b as A;//不用as,进行强制转换,如果类型不匹配,会引发转换异常A a = (A) b;