Backward compatibility of UIWindow rootViewController

Question

When creating a new Xcode 4 view based project, it creates that line on the applicationDelegate didFinishLaunching method :

self.window.rootViewController = self.viewController;

But the attribute rootViewController only appears with iOS 4.0.

What may I write here to be compatible with iOS prior to 4.0?

P.S. : Because of some problems, I won't be able to test the solution, so please it should be ok.

Answer 1

Use introspection to detect if UIWindow class has that property at runtime and if it doesn't, just add view controller's view as subview to the window.

if ([UIWindow instancesRespondToSelector:@selector(rootViewController)]) {
    self.window.rootViewController = self.viewController;
} else {
    [self.window addSubview:self.viewController.view];
}