URLWithString拼接NSURL为nil的问题

出现原因：

This method expects URLString to contain any necessary percent escape codes, which are ‘:’, ‘/’, ‘%’, ‘#’, ‘;’, and ‘@’. Note that ‘%’ escapes are translated via UTF-8.

解决方法

NSString * string = @"xxxx;
NSString * urlStr = [string stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSURL * url = [NSURL URLWithString:urlStr];