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I'm writing an Universal App that will run natively on both iPad and iPhone. I also need it to be targeted to older devices (those that cannot run 4.0) so 3.1 is a must.

I have already set up the Base SDK to the latest available version (4.2), and the Deployment Target to 3.1. I am making lots of runtime checks in order to call the corresponding methods only on the right device/version.

One of the things I am making use of in the iPad is an UISplitViewController. When assigning the splitViewController delegate, the compiler throws a warning because the class interface isn't explicitly adopting the UISplitViewControllerDelegate protocol and I'm afraid that if I declare it to make it so, the App will crash on older devices where there is no UISplitViewController/UISplitViewControllerDelegate.

What is the best way to supress the compiler warning? Should I declare an 'empty' UISplitViewControllerDelegate? If so, can I make it conditionally at runtime? Or should I just make the corresponding class interface conform to the protocol and not worry about older devices?

Best,

boliva
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3 Answers3

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You can suppress the warning with a simple C cast:

foo.delegate = (id<UISplitViewControllerDelegate>)self;
Darren
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1

I haven't tried this, but I'm pretty sure you can just go ahead and adopt the protocol unconditionally, even if the class may be used on an older runtime that does not have the protocol. And here's why:

All the information for defining a protocol is contained in the .h file that declares the @protocol. When you adopt a protocol, that protocol declaration is imported at some point in your .h file (presumably by #import <UIKit/UIKit.h>).

When the runtime needs to know something about a protocol, it references a "Protocol Object", which you would normally reference in source code by doing @protocol(MyProtocolName). And the compiler creates this protocol object (at compile time) when such a protocol reference is encountered, according to the section titled Protocol Objects in The Objective-C Programming Language documentation.

So knowing all that, if you adopt a protocol and you write any code that references the protocol object, that protocol object will be created by the compiler. Even if you're running on an older device, the compiler should've created that protocol object for you, so I don't think it'll cause a crash.

Hope that makes sense. If I have some time I can try this out to see if it holds in practice because I have devices running a range of iOS versions from 3.1 to 4.2.

Daniel Dickison
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Same problem if you want to use printing and stil have the app runnig before 4.2. Basically it works with this

#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 40200
// code for iOS 4.2++
@interface PersonDetailViewController : UITableViewController <EditViewControllerDelegate, EditPickerViewControllerDelegate, UITextFieldDelegate, UIActionSheetDelegate, UINavigationControllerDelegate, UIImagePickerControllerDelegate, UIPrintInteractionControllerDelegate>{
#else
// code for iOS til 4.1
@interface PersonDetailViewController : UITableViewController <EditViewControllerDelegate, EditPickerViewControllerDelegate, UITextFieldDelegate, UIActionSheetDelegate, UINavigationControllerDelegate, UIImagePickerControllerDelegate>{
#endif

But... It looks like the InterfaceBuilder can't handle this. All outlets defines after this conditional definition ar gone in IB.

So any better solution?

Regards Gerd

Gerd
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