如何基于现有用户或返回用户iOS加载不同的应用程序视图？

Question

如果我是第一次加载应用程序，它会进入正确的调查视图，但是当我通过双击主页按钮关闭应用程序并从iphone底部退出时，然后重新打开应用程序，应用程序崩溃而不是正确转到返回的用户视图控制器，这个视图控制器只是名为viewController，调查一个是surveyViewController ...

以下代码不起作用：

AppDelegate.h：

#import <UIKit/UIKit.h>

@class ViewController;
@class SurveyViewController;

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;
@property (strong, nonatomic) SurveyViewController *home;
@property (strong, nonatomic) ViewController *home2;

@property (nonatomic, retain) UINavigationController *navController;
@property (nonatomic, retain) UINavigationController *navController2;
@property (strong, nonatomic) ViewController *viewController2;
@property (strong, nonatomic) SurveyViewController *viewController;

@end

AppDelegate.m：

#import "AppDelegate.h"

#import "ViewController.h"
#import "SurveyViewController.h"

@implementation AppDelegate

@synthesize window = _window;
@synthesize viewController = _viewController;
@synthesize viewController2 = _viewController2;
@synthesize home, home2, navController, navController2;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    if ([[NSUserDefaults standardUserDefaults] boolForKey:@"HasFilledSurvey"] == NO) {

        home = [[SurveyViewController alloc] initWithNibName:@"SurveyViewController" bundle:nil];
        self.navController = [[UINavigationController alloc]initWithRootViewController:home];
        self.window.rootViewController = self.navController;

        [[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"HasFilledSurvey"];

    }
    else {

        home2 = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
        self.navController2 = [[UINavigationController alloc]initWithRootViewController:home2];
        self.window.rootViewController = self.navController2;

    }

    [self.window makeKeyAndVisible];
    return YES;
}

谢谢