UITextView with multiple delegates?

I have a UITextView that p开发者_JAVA百科oints to the File's Owner as its delegate, and I have a number of the delegate functions implemented. However, I would also like to point to a second object (in this case a TextExpander object, http://www.freshblocks.com/tutorials/how-to-add-textexpander-touch-sdk-to-iphone-apps/) also as a delegate. How might this be possible? As far as I know there can only be one delegate in objective-c.

I don't know the specific of TextExpander but he delegate design pattern assumes one and only one delegate. You can't have two delegates for one object.

There are ways around this. You could designate one of the delegates as the primary delegate and implement all the methods in this class. That class could then simple call the secondary delegate for the required methods. This is the simplest approach but does result in the primary delegate becoming tightly coupled with the secondary delegate.

Another approach would be to resolve the messages dynamically and use message forwarding. You would still require the a primary/secondary delegate pattern, but instead of the primary delegate needing to implement all the methods it would simply pass all messages it doesn't respond to onto the secondary delegate. This approach means that the secondary delegate can change by adding/removing additional delegate methods without having to change the primary delegate. The key method is - (id)forwardingTargetForSelector:(SEL)sel. See Objective-C Message Forwarding for a good explanation.

It seems that they solve this in step 5, by setting [textExpander setNextDelegate:self]; before setting the textExpander object as the "primary" delegate of the view.

I don't have the code myself so I haven't tried it, though, and their documentation is... well not.

Just for information: Delegates are not an Objective-C feature, but a design pattern using though Cocoa/Cocoa-touch.

Delegate pattern allow only one object to be notified of the changes of another. The solution to have an intermediate delegate object could be an easy way of doing things.

If you want to keep your code clean and reduce the coupling you might use another pattern known as KVO (Key Value Observing). Apple provides a good guide on how to use it.

In KVO a single object, that needs to be KVC (Key Value Coding) compliant, can notify multiple objects without even knowing about it. It uses an intermediate notifier object (singleton for you application).

Check the Apple doc on KVC + KVO and you shall be able to do what you want.

I have a class with the protocol NSXMLParserDelegate implemented. I call this ParserHelper. I parse a lot of XML which happen to have some tags in all of them and i have about 20 parsers (one for each type of XML), and i didnt want to implement it over and over again.

So, I subclassed my ParserHelper class 20 times, adding in each subclass the required tags/behaviours like CaseAParser, CaseBParser and so on...

I just implement the delegate methods i needed and called it on the superclass once i'm done with the method.

I assume it works on every delegate.

This way, all you need is to make your class a subclass of SMTEDelegateController and implement the methods you need, remembering to call the [super whatEverMethod:andParameters] at the end of your functions and you should be good to go.