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Hi all,

If I have a touch event that is caught in my (UIView *) view (as this is the only place touch events can be caught, I believe) does anyone know how I can handle that event in my AppDelegate? I've been looking into the Responder Chain documentation but can't get it to work in practice. I've got as far as the viewController handling the message but can't get it to go any further up the chain.

Thanks for any help anyone can provide

Paz

HarryWang said:

I don't think your AppDelegate will be able to handle a response.  AppDelegates usually inherit from the NSObject class and implement the UIApplicationDelegate protocol.  A responder inherits from the UIResponder base class (which of course inherits from the NSObject).

Maybe when declaring your AppDelegate, instead of inheriting from NSObject, inherit from NSResponder instead?  Don't know if it will need to “register” itself somewhere to receive the event notifications.

From the Apple docs:

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A responder object is an object that can respond to events and handle them. UIResponder is the base class for all responder objects. It defines the programmatic interface not only for event handling but for common responder behavior. UIApplication, UIView, and all UIKit classes that descend from UIView (including UIWindow) inherit directly or indirectly from UIResponder.

The first responder is the responder object in the application (usually a UIView object) that is the current recipient of touches. A UIWindow objects sends the first responder an event in a message, giving it the first shot at handling the event. If the first responder doesn’t handle the event, it passes the event (via message) to the next responder in the responder chain to see if it can handle it.

The responder chain is a linked series of responder objects. It allows responder objects to delegate responsibility for handling an event to other, higher-level objects. An event proceeds up the responder chain as the application looks for an object capable of handling the event. The responder chain consists of a series of “next responders” in the following sequence:

1. The first responder passes the event to its view controller (if it has one) and then on to its superview.

2. Each subsequent view in the hierarchy similarly passes to its view controller first (if it has one) and then to its superview.

3. The topmost enclosing view passes the event to the UIWindow object.

4. The UIWindow object passes the event to the singleton UIApplication object.

If the application finds no responder object to handle the event, it discards the event.

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Good luck.

Harry “doesn't know if that will introduce more overhead though” Wang

Hi Harry,

Thanks for your help. In fact your suggestion and some further reading led me to insert a main controller between my appDelegate and my viewControllers to handle these type of events and it seemed to work.

The docs I've been reading regarding the Responder chain to them have a distinct MAC OS feel to them rather than anything specific for the iPhone. May I ask where you found the information you sent to me?

Thanks again.

Paz