-[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object' 解决方法

-[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object' 解决方法：
错误：NSMutableDictionaryd =[[[NSUserDefaults standardUserDefaults] objectForKey:@"xxxx"] mutableCopy];
修改：NSMutableDictionaryd =[NSMutableDictionary dictionaryWithDictionary:[[NSUserDefaults standardUserDefaults]ValueForKey:@"xxxx"]];