iPhone Programming - How do I programmatically make a view that requires two delegates?

Here is my dilemma. I would like to have a text box and a button. The user types in text and then presses the button. Once the button is pressed, a text message window (using MFMessageComposeViewController) comes up. I don't know how to set this up. The problem is that the TextBox will require a delegate (UITextFieldDelegate) and the MFMessageComposeViewController will require an MFMessageComposeViewControllerDelegate. How can I have a .h file that declares a view that is more than one delegate?

I'm new to iPhone programming so any help on how to have an interface view that handles more than one delegate (so that I can have multiple types of controls in my view) would be really helpful!


A delegate does not need to be a view. Indeed, in most cases it probably shouldn't be. Often you will make a controller object the delegate, although this depends a lot on what you're doing.

The delegate protocols you need (MFMessageComposeViewControllerDelegate and UITextFieldDelegate) are quite distinct, so a single object can readily implement the methods of both without any confusion. But even if you are the same delegate type for several objects, the methods will be passed a pointer to the calling object so you can decide what to do case-by-case if necessary.

If you just mean how do you declare your class as implementing both protocols, you would do this:

@interface MyDelegate : NSObject <MFMessageComposeViewControllerDelegate, UITextFieldDelegate>

...although this presupposes that the protocols are formally required, which I don't think is the case here. In which case such a protocol list is unnecessary.

Otherwise, I probably am not understanding your question...

EDIT: OK, it seems like what you're looking for is how to link up the delegates at runtime. This varies according to the particular class, but for MFMessageComposeViewController you do this:

MFMessageComposeViewController* composer = ...;
id<MFMessageComposeViewControllerDelegate>* delegate = ...;
composer.messageComposeDelegate = delegate;

Easy, no? In this case the protocol is required, so you'd have to include it in the interface as described previously.

In general, if an object uses a delegate for anything, it will have a property or a method to allow you to set it, which you'll find in the documentation. Eg, in this case: Properties for MFMessageComposeViewController.

Note that delegate properties are conventionally weak references, so the objects in question need to be retained somewhere in your application.

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