将字符串切割成数组&将数组元素拼接成字符串

将string字符串转换为array数组
NSArray *array = [Str componentsSeparatedByString:@","];//@","是分隔符

将array数组转换为string字符串
NSString *tempString = [mutableArray componentsJoinedByString:@","];//@","是分隔符