-[NSNull countByEnumeratingWithState:objects:count:]:

当数组为空时遍历数组容易出这样的问题， -[NSNull countByEnumeratingWithState:objects:count:]: unrecognized selector sent to instance 0x3e4e85e0

 解决办法就是在遍历数组之前先要判断

if (![array isKindOfClass:[NSNull class]])

{

　　for循环

}