语义问题：不兼容的指针警告

Question

我已经启用ARC，在我didFinishLaunchingWithOptions方法，我写了下面的代码：

AppDelegate.h：

@interface AppDelegate : UIResponder <UIApplicationDelegate> 

@property (strong, nonatomic) UIWindow *window; 

@property (strong, nonatomic) ViewController *viewController; 

@end 

AppDelegate.m：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{ 
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; 
    // Override point for customization after application launch. 
    ViewController * vc = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil]; 
    UINavigationController * nav = [[UINavigationController alloc] initWithRootViewController:vc]; 
    self.viewController = nav; 
    self.window.rootViewController = self.viewController; 
    [self.window makeKeyAndVisible]; 
    return YES; 
} 

但声明：self.viewController = nav;得到编译警告，警告信息是：

file://.../AppDelegate.m: warning: Semantic Issue: Incompatible pointer types passing 'UINavigationController *__strong' to parameter of type 'ViewController *'

如何删除警告？

谢谢。

Answer 1

我认为视图控制器是UIViewController中的自定义子类，或者是完全不同的或的UINavigationController本身的子类。这就是为什么它是错误的：超类不能完全作为其子类（例如，它可能没有某些属性/方法等），因此是警告。

Answer 2

编译器告诉你：“nav，一个UINavigationController的实例，不是'ViewController'或'ViewController'的子类”。如果你真的想留住这两个导航控制器和您的视图控制器，你可以添加第二个属性：

@property (nonatomic, strong) UINavigationController *navController; 

然后将其设置在application:didFinishLaunchingWithOptions:

self.viewController = vc; 
self.navController = nav; 

另一个这里的解决方案将只需抓住导航控制器并使用'topViewController'属性来访问您的VC。

编辑：或更好的是，不关心导航控制器。简单地做：

self.viewController = vc; 
self.window.rootViewController = nav; 

Answer 3

，你可以做这样的

self.viewController =[nav.viewControllers objectAtIndex:0]; 

话，就不会显示出像

Answer 4

尝试“过客‘的UINavigationController * __强’到类型的参数“视图控制器*不兼容的指针类型”的警示以下代码： -

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{ 
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; 
    // Override point for customization after application launch. 
    self.viewController = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil]; 
    UINavigationController * nav = [[UINavigationController alloc] initWithRootViewController:self.viewController]; 

    self.window.rootViewController = nav; 
    [self.window makeKeyAndVisible]; 
    return YES; 
}