語義問題：不兼容的指針警告

Question

我已經啓用ARC，在我didFinishLaunchingWithOptions方法，我寫了下面的代碼：

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; 
} 

但聲明：self.viewController = nav;得到編譯警告，警告信息是：

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

如何刪除警告？

謝謝。

Answer 1

我認爲視圖控制器是UIViewController中的自定義子類，或者是完全不同的或的UINavigationController本身的子類。這就是爲什麼它是錯誤的：超類不能完全作爲其子類（例如，它可能沒有某些屬性/方法等），因此是警告。

Answer 2

編譯器告訴你：「nav，一個UINavigationController的實例，不是'ViewController'或'ViewController'的子類」。如果你真的想留住這兩個導航控制器和您的視圖控制器，你可以添加第二個屬性：

@property (nonatomic, strong) UINavigationController *navController; 

然後將其設置在application:didFinishLaunchingWithOptions:

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

另一個這裏的解決方案將只需抓住導航控制器並使用'topViewController'屬性來訪問您的VC。

編輯：或更好的是，不關心導航控制器。簡單地做：

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

Answer 3

，你可以做這樣的

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

話，就不會顯示出像

Answer 4

嘗試「過客‘的UINavigationController * __強’到類型的參數「視圖控制器*不兼容的指針類型」的警示以下代碼： -

- (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; 
}