iOS每次启动都提示：Application windows are expected to have a root view controller at the end of application launch，怎么解决？

运行一次iOS项目，每次启动虽然显示Successed，但控制台都提示：Application windows are expected to have a root view controller at the end of application launch，该怎么解决？

Xcode7.0 只需在AppDelegate.m的didFinishLaunchingWithOptions添加如下一行代码即可：

self.window.rootViewController = [[UIViewController alloc]init];

这个问题是我在学习《IOS编程》第4章创建Hypnosister项目时遇到的，该书在编写的时候基于Xcode5，作者就没有提到这个问题。

现在，我的具体代码及解决办法如下:

//
//  BNRAppDelegate.m
//  Hypnosister


#import "BNRAppDelegate.h"
#import "BNRHypnosisView.h"

@implementation BNRAppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.

    CGRect firstFrame = self.window.bounds;

    BNRHypnosisView *firstView = [[BNRHypnosisView alloc] initWithFrame:firstFrame];

    [self.window addSubview:firstView];
    
    self.window.rootViewController = [[UIViewController alloc]init];//加在这里！

    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application
{
    // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
    // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. 
    // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
}

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    // Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}

- (void)applicationWillTerminate:(UIApplication *)application
{
    // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
}

@end