NSData to NSString and NSString to NSData
2011-07-19
哎，经常忘记。 年纪大了记忆力越来越差了！
NSDate to NSString:
NSString * str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
NSString to NSData:
NSData * data
data = [str dataUsingEncoding:NSUTF8StringEncoding];