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Cocoa uses delegates extensively to provide (among other things) callback methods for asynchronous operations. However, I personally hate the delegate model and how it pollutes the current class with handlers for very specific child operations. UIAlertView is a perfect example.
Therefore, I'm wondering if it's possible to simply create an anonymous delegate object that meets the requirements of a delegate protocol (such as UIAlertViewDelegate) via blocks and pass this anonymous object wherever a delegate reference is expected.
I imagine something like so:
id myDelegate = @{
alertView:alertView didDismissWithButtonIndex:index = ^ {
...
}
};
UIAlertView* alertView = [[UIAlertView alloc] initWithTitle:... message:... delegate:myDelegate cancelButtonTitle:... otherButtonTitles:...;
[alertView show];
I've heard Objective-C has some good dynamic language features but I don't know how to simply add a method/selector to an object. Can this be done in a relatively straightforward manner?
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To create one, you define a class that implements the delegate methods you're interested in, and mark that class as implementing the delegate protocol. Then you could create an instance of MyClass and assign it as the web view's delegate: MyClass *instanceOfMyClass = [[MyClass alloc] init]; myWebView.
A delegate is an object that acts on behalf of, or in coordination with, another object when that object encounters an event in a program. The delegating object is often a responder object—that is, an object inheriting from NSResponder in AppKit or UIResponder in UIKit—that is responding to a user event.
In Objective-C, you add the protocol name in angle brackets beside the class interface declaration. MyClass is declaring that it conforms to SampleProtocol below. MyClass will also have to provide an implementation for “someMethod” in the implementation file because it is a required protocol method.
Yes, the language features you mention are exposed via the objective-c runtime, although there's no built-in facility to dynamically create delegate classes and the runtime api is not the friendliest of things.
There is a library called A2DynamicDelegate, which does exactly what you're talking about. I haven't used it, but it may be worth investigating.
EDIT: A problem with this approach is that delegates are not retained, so you'll need to either keep a strong reference somewhere else, or an add an associative reference to the UIAlertView. You may find that all this fuss isn't worth it and just adding an extra method to your view controller works better (you can conform to the delegate protocol in a class extension to avoid polluting your interface).
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