iOS - 以編程方式添加/刪除子視圖

Question

好吧我想添加一個UIImageView作爲子視圖，然後在啓動屏幕的方式幾秒鐘後將其刪除。我發現了三種不同的方法，但根據Objective-C和Apple的說法，我不明白哪一種方法是最好的。

以下是在三種不同的方法：

1） 在第二種方法中我MyAppDelegate.h

@interface MyAppDelegate : NSObject <UIApplicationDelegate> { 

    MyViewController *myViewController; 
    UIImageView *myImageView; 
} 


@property (nonatomic, retain) IBOutlet MyViewController *myViewController; 
@property (nonatomic, retain) IBOutlet UIWindow *window; 

@end 

和MyAppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{ 
    myImageView =[[UIImageView alloc] initWithFrame:CGRectMake(0.0,0.0,self.window.frame.size.width,self.window.frame.size.height)]; 

     myImageView.image=[UIImage imageNamed:@"Yoga.png"]; 


    [self.window addSubview:myImageView ]; 
    [self.window bringSubviewToFront:myImageView]; 

    [self performSelector:@selector(removeImage) withObject:nil afterDelay:2.5]; 

    return YES; 
} 

-(void) removeImage 
{ 
    [myImageView removeFromSuperview]; 

    [myImageView release]; 

    [self.window addSubview:myViewController.view]; 
    [self.window makeKeyAndVisible]; 
} 

2）：

In my MyAppDelegate.h 


@interface MyAppDelegate : NSObject <UIApplicationDelegate> { 

    MyViewController *myViewController; 
    UIImageView *myImageView; 
} 

@property (nonatomic, retain) IBOutlet UIImageView *myImageView; 

@property (nonatomic, retain) IBOutlet MyViewController *myViewController; 
@property (nonatomic, retain) IBOutlet UIWindow *window; 

@end 

和MyAppDelegate.m

@synthesize myImageView;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{ 
    myImageView =[[UIImageView alloc] initWithFrame:CGRectMake(0.0,0.0,self.window.frame.size.width,self.window.frame.size.height)]; 

     myImageView.image=[UIImage imageNamed:@"Yoga.png"]; 


    [self.window addSubview:myImageView ]; 
    [self.window bringSubviewToFront:myImageView]; 

    [self performSelector:@selector(removeImage) withObject:nil afterDelay:2.5]; 

    return YES; 
} 

-(void) removeImage 
{ 
    [myImageView removeFromSuperview]; 

    [myImageView release]; 

    [self.window addSubview:myViewController.view]; 
    [self.window makeKeyAndVisible]; 
} 

- (void)dealloc 
{ 
    [myViewController release]; 
    [myImageView release]; 
} 

3）第三種方法：

In my MyAppDelegate.h 


@interface MyAppDelegate : NSObject <UIApplicationDelegate> { 

    MyViewController *myViewController; 

} 

@property (nonatomic, retain) IBOutlet MyViewController *myViewController; 
@property (nonatomic, retain) IBOutlet UIWindow *window; 

@end 

和MyAppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{ 
    UIImageView *myImageView =[[UIImageView alloc] initWithFrame:CGRectMake(0.0,0.0,self.window.frame.size.width,self.window.frame.size.height)]; 

    myImageView.image=[UIImage imageNamed:@"Yoga.png"]; 
    myImageView.tag=22;  

    [self.window addSubview:myImageView ]; 

    [myImageView release]; 

    [self.window bringSubviewToFront:myImageView]; 

    [self performSelector:@selector(removeImage) withObject:nil afterDelay:2.5]; 

    return YES; 
} 

-(void) removeImage 
{ 

    for (UIView *subview in [self.view subviews]) { 

    if (subview.tag == 22){ 

     [subview removeFromSuperview]; 

    } 

} 
    [self.window addSubview:myViewController.view]; 
    [self.window makeKeyAndVisible]; 
} 

- (void)dealloc 
{ 
    [myViewController release]; 

} 

所以總結起來..第一種方法不使用屬性爲的UIImage只有一個變量，第二個使用屬性，第三個只創建UIImage並將其添加爲子視圖，然後根據其標記刪除它。

哪一種是正確的方法。我相信所有三個選項聽起來都是正確的..但有沒有我應該遵循的某種方式。這些選項在內存和性能方面是否更好？

由於提前，

安德烈亞斯

Answer 1

如果你不打算再次使用的圖像，也沒有必要的指針保持它。此外，如果您使用IBOutlet，則還需要在IB中添加視圖。在這個特定的例子中，我會說選項3最有意思，特別是考慮到這個選擇，你可以從標準的「視圖爲基礎的應用程序」模板開始，只需添加關於圖像視圖的位並將其餘的單獨留下。最後一個選擇3的觀察; 2條消息到窗口;

[self.window addSubview:myViewController.view]; 

[self.window makeKeyAndVisible]; 

似乎超出了任何方法的範圍。這可能只是複製和粘貼錯誤，但請注意它們應位於「didFinishLaunchingWithOptions：」

Answer 2

您可以使用附加到視圖圖層的動畫。下面的代碼淡化了視圖 - 但還有很多其他方法可以將其刪除。 （您需要連接QuartzCore框架）

myImageView.layer.opacity = 0.0; 
// this is the state the view will be in after the animation (e.g. invisible) 

CABasicAnimation *theFade; 

theFade = [CABasicAnimation animationwithKeyPath:@"opacity"]; 
theFade.duration = 10.0; 
theFade.fromValue = [NSNumber numberWithFloat:1.0]; // i.e. visible 
theFade.toValue = [NSNumber numberWithFloat:0.0]; // i.e. invisible 
[myImageView.layer addAnimation:theFade forKey:@"animateOpacity"];