How do I run a universal app on the iPhone 3.1.3 simulator?

I'm working on a new app that I want to be universal for the iPhone and iPad. I started out with the "Create a Window-based app" wizard, and it created separate app delegates in "iPhone" and "iPad" groups. Since I already was quite familiar with iPhone dev, I did that part of my project, and now I'm ready to do some iPad stuff.

So... I started out by adding a UISplitViewController to my iPad delegate, switch the Active SDK to 3.2, and it works! But when I switch back to 3.1.3, and try to run it in the simulator, Build and Go fails. For starters, I see:

...path.../iPad/AppDelegate_Pad.h:13: error: expected specifier-qualifier-list before 'UISplitViewController'

I've got my Base SDK set to 3.2 and my Deployment Target set to 3.1.3. I thought that was enough. But I also have found in the documentation this method to conditionally compile:

#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 30200
   MyIPadViewController* vc;
// Create the iPad view controller
#else
   MyIPhoneViewController* vc;
// Create the iPhone view controller
#endif

So do I need to do this everywhere? It seems like an awful 开发者_如何学运维lot of code to add (that I'll be getting rid of in a short time for 4.0 anyway) so I feel like I must be doing something wrong. And, I don't even have any idea how this works for things like @property or @synthesize declarations.

tl;dr version of the question - did I miss a setting somewhere?

I use this C function to help keep the code concise:

BOOL isPad() {
    return (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad);
}

Another thing I do, when I have different xib files for iPhone vs iPad. I have a stripPadSuffixOnPhone() function that helps keep the code simpler:

// Load/create the Delete table cell with delete button
self.deleteCell = [Utilities loadNib:stripPadSuffixOnPhone(@"DeleteCell~ipad") 
                           ClassName:@"DeleteCell" 
                   Owner:self];

Things like that can make coding more straightforward and a lot less conditionals. Still have to test everything twice though.

Quite the opposite. A universal app runs the same binary on iPhone and iPad so you cannot use conditional compilation to differentiate between the two version. But you need to use the macro Apple cites in the documentation:

if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
    // iPad-specific code
} else {
    // iPhone-specific code
}

Here's what works for me:

1. Build your app using SDK 3.2.
2. Switch the active SDK to iPhone Simulator 3.1.3 (or whatever).
3. From the Run menu select Debug (not Build and Debug).

The binary built under 3.2 will be installed in the 3.x simulator without rebuilding. When you are finished don't forget to set your active SDK back to 3.2.