编译Xcode项目应用程序窗口需要有一个根视图控制器

Question

如何修复此错误?iphone模拟器工作，但当我使用ipad时，我在控制台得到这个…2013-05-25 20:59:17.556你的rss [2717:c07]应用程序窗口应该在应用程序启动结束时有一个根视图控制器

    //
//  AppDelegate.m
//  YourRSS
//
//  Created by Mohammad Komeili on 5/17/13.
//  Copyright (c) 2013 MOMEKS. All rights reserved.
//
#import "AppDelegate.h"
#import "ViewController.h"
#import "ViewController_iPad2.h"

@implementation AppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] ;
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        self.viewController = [[ViewController alloc] initWithNibName:@"ViewController_iPhone" bundle:nil];
        self.navigationController = [[UINavigationController alloc] initWithRootViewController:self.viewController];
    }
  /*  }else{
        self.viewController = [[ViewController alloc] initWithNibName:@"ViewController_iPad2" bundle:nil];
        self.navigationController = [[UINavigationController alloc] initWithRootViewController:self.viewController];
    }
    */
    self.navigationController.navigationBarHidden = YES;
    self.window.rootViewController = self.navigationController;
    [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

Answer 1

被注释掉的代码部分是如果你不是在iPhone上执行的代码(参见:UIUserInterfaceIdiomPhone)。因为你在iPad上跳过了导航控制器的创建，所以它仍然是nil…这给了你一个明显的错误