Question

I have developed a generic controller for sliding UIView and I manage UIViewController (and obviously subclass ) and must call a specific method (freeze) only if a subclass of UIViewController respond to this method:

-(void)freezeRootViewController
{
    if([_rootViewController respondsToSelector:@selector(freeze)])
        [ ((id) _rootViewController) freeze];
}

I don’t know the class of _rootViewController but I know it is a subclass of UIViewController, for this reason I have tried to cast my _rootViewController to ID, but I can’t compile:

Environment: XCode 4.5.1, iOs 4.3+ with ARC

Error: “No know instance method for selector ‘freeze'”

Note: I CAN’T force the developer to use a specific UIViewController subclass for the _rootViewController.

Answer 1

This seems to be a warning rather than an error – you should be able to compile your code and just ignore this diagnostic message. However, if you want to get rid of it completely, you can declare a protocol and do the cast as follows:

@protocol MyProtocol <NSObject>

- (void)freeze;

@end

[(id <MyProtocol>)_rootViewController freeze];