Warning while adding and using a new method in external library protocol

问题

I am using a external library and one of my view controller is registering as delegate for a class in that framework. Now, at one place I want to execute some code on this delegate class. I am writing a method for that and calling it on my delegate.

Now, all works fine but I am getting a warning that this newly added method is not part of the protocol.

This is my Class:

@protocol MyExtendedDelegate <LibraryDelegate>

@optional

- (void)actionTaken;

@end

@interface MyController : UITableController <MyExtendedDelegate> {  

}

@end

And inside my controller I am registering self as delegate for library controller

LibraryController *libController = [[LibraryController alloc] init];
    libController.delegate = self;

Finally, This is the code in a separate class where I am calling this method:

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
    if ([self.libraryController.delegate respondsToSelector:@selector(actionTaken)]) {
        [self.libraryController.delegate actionTaken];
    }

Here is the warning I am getting:

-- actionTaken not found in protocol
-- NSObject may not respond to actionTaken

I want to get rid of this warning. Any idea.

回答1:

The property libraryController.delegate is defined in the external library to conform to LibraryDelegate. Try to downcast to MyExtendedDelegate before you call the method from your extended protocol.

if ([self.libraryController.delegate conformsToProtocol:@protocol(MyExtendedDelegate)])
{
    id<MyExtendedDelegate> extendedDelegate = (id<MyExtendedDelegate>)self.libraryController.delegate;
    if ([extendedDelegate respondsToSelector:@selector(actionTaken)])
    {
        [extendedDelegate actionTaken];
    }
}

回答2:

Write a new protocol that extends the old one, and conform to that, something like:

@protocol MyNewProtocol <OtherProtocol>
   - (void) myCoolMethod;
@end

回答3:

(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex { if ([self.libraryController.delegate respondsToSelector:@selector(actionTaken)]) { [self.libraryController.delegate performSelector:@selector(actionTaken)]; }

Using performSelector instead of directly calling a method will remove warning for sure.

来源：https://stackoverflow.com/questions/5768725/extending-a-protocol-defined-in-external-lib

标签

iphone

objective-c

cocoa-touch

ios

delegates