You can use the as operator to perform certain types of conversions between compatible reference types or nullable types.
The as operator is like a cast operation. However, if the conversion isn‘t possible, as returns null instead of raising an exception. Consider the following example:
expression as type
The code is equivalent to the following expression except that the expression variable is evaluated only one time.
expression is type ? (type)expression : (type)nullNote that the as operator performs only reference conversions, nullable conversions, and boxing conversions. The as operator can‘t perform other conversions, such as user-defined conversions, which should instead be performed by using cast expressions.
原文地址：http://blog.csdn.net/troubleshooter/article/details/40543763
