Questions about Universal application in Xcode 4 - iphone

Question

I am trying to build an universal application with Xcode 4. However, it seems a little different from past versions.
My project utilizes the View Based Application template. My issue is that I added a UIViewController subclass which has one nib file for iPad. How do I create another nib file with the same class targeted instead for iPhone? Also, how do I ensure that the proper nib file is loaded for the proper platform?
EDITED :
here is my code :
- (IBAction)BookView {
if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
BookViewController *viewController = [[BookViewController alloc] initWithNibName:#"BookViewController" bundle:nil];
[self presentModalViewController:viewController animated:YES];
} else {
BookViewController *viewController = [[BookViewController alloc] initWithNibName:#"BookViewController_iPad" bundle:nil];
[self presentModalViewController:viewController animated:YES];
}
}

Answer 1

Step 1: Create for iPhone:
New file / ios / cocoa touch / UIViewController subclass
uncheck Targeted for iPad
check with XIB
This step will create .m .h and .xib files with same name, for example: CustomView
Step 2: Create new XIB for iPad:
New file / ios / user interface / view
device family iPad
for convenience choose the same name with suffix _iPad (for example CustomView_iPad)
in this xib go to File's Owner, in the inspector tabs choose identity inspector, custom class and choose the same name of class created in step 1.
Connect IBOutlets.
In your code use something like this:
if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
CustomView *viewController = [[CustomView alloc] initWithNibName:#"CustomView" bundle:nil];
} else {
CustomView *viewController = [[CustomView alloc] initWithNibName:#"CustomView_iPad" bundle:nil];
}
Good luck!

Answer 2

Name your xib file for iPad BookViewController~ipad.xib and the iPhone one BookViewController~iphone.xib. Then load the nib file as usual:
BookViewController *viewController = [[BookViewController alloc] initWithNibName:#"BookViewController" bundle:nil];
[self presentModalViewController:viewController animated:YES];
When the app runs on an iPad device, the ~ipad xib will be automatically loaded. If the app runs on an iPhone, the ~iphone xib will be automatically loaded.
Note that ~ipad and ~iphone suffixes are case sensitive. If you name it ~iPad for instance, you'll get a runtime exception that the nib file is not found.