IOS，刪除警告？

Question

我想刪除這條線警告：

UIViewController * appController = [[[UIApplication sharedApplication] delegate]  viewController]; 

我得到這一行代碼的警告是： 「實例方法‘的viewController’未找到（返回類型默認爲‘身份證’ ）

有人能幫助解釋如何我可能會刪除這個虧

非常感謝，

Answer 1

您需要投下您的應用程序委託：

UIViewController * appController = [(MyAppDelegate *)[[UIApplication sharedApplication] delegate] viewController]; 

Answer 2

添加投放到您的委託：？

UIViewController * appController = [(MyAppDelegate *)[[UIApplication sharedApplication] delegate] viewController]; 

Answer 3

我不知道你的...AppDelegate是如何被調用的，所以我在這裏使用DemoAppDelegate。

UIViewController *appController = [(DemoAppDelegate *)[[UIApplication sharedApplication] delegate] viewController]; 

Answer 4

類型轉換是嘈雜，可能是危險的。爲了解決這個問題，我通常最終創建一個簡單的類方法。假設類是一直打算用作應用程序的委託，你可以寫這樣的事情：

// MONApplicationDelegate.h 
@interface MONApplicationDelegate : NSObject <UIApplicationDelegate> 

// ... 

+ (MONApplicationDelegate *)sharedApplicationDelegate; 
- (UIViewController *)viewController; 

@end 

// MONApplicationDelegate.m 
@implementation MONApplicationDelegate 

// ... 

+ (MONApplicationDelegate *)sharedApplicationDelegate 
{ 
    id ret = [[UIApplication sharedApplication] delegate]; 
    if (nil == ret) { 
     assert(0 && "oops - app delegate has not been created yet"); 
     return nil; 
    } 
    if (![ret isKindOfClass:[MONApplicationDelegate class]]) { 
     assert(0 && "invalid class type for shared application delegate"); 
     return nil; 
    } 
    else { 
     return ret; 
    } 
} 

@end 

// in action 
UIViewController * appController = 
    [[MONApplicationDelegate sharedApplicationDelegate] viewController]; 

// which is shorter and safer to use, when compared to: 
UIViewController * appController = 
    [(MONApplicationDelegate*)[[UIApplication sharedApplication] delegate] viewController];