iOS重新设置window的rootViewController

有xib文件时的写法

• (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
[_window release];
// Override point for customization after application launch.
RootViewController *rootVC = [[RootViewController alloc] initWithNibName:@"RootViewController" bundle:nil];
//默认从包里边来找,所以是nil
self.window.rootViewController = rootVC;
[rootVC release];
self.window.backgroundColor = [UIColor redColor];
[self.window makeKeyAndVisible];
return YES;
}