iOS - 以编程方式添加/删除子视图

Question

好吧，我想添加一个 UIImageView 作为子视图，然后以启动屏幕的工作方式在几秒钟后将其删除。我发现了三种不同的方法来做到这一点，但我不明白根据 Objective-C 和 Apple 的说法，哪一种是最好的方法。

以下是三种不同的方法：

1） 在我的 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) 中，第二种方法：

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

在 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）在第三种方法中：

In my MyAppDelegate.h


@interface MyAppDelegate : NSObject <UIApplicationDelegate> {

    MyViewController *myViewController;

}

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

@end

在MyAppDelegate.m中

   - (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];

 }

所以总结一下..第一种方法不使用UIImage的属性，只有一个变量，第二个方法使用属性，第三个方法只是创建UIImage并添加它作为子视图，然后根据其标签将其删除。

这是正确的方法。我相信所有三个选项听起来都是正确的。但是我应该遵循什么特定的方法。这些选项在内存和性能方面是否更好？

预先感谢，

安德烈亚斯

Answer 1

您可以使用附加到视图层的动画。下面的代码使视图淡出 - 但还有许多其他方法可以删除它。 （需要附加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"]; 

Answer 2

如果您不打算再次使用该图像，则无需保留指向它的指针。此外，如果您使用IBOutlet，您还需要在IB中添加视图。在这个具体示例中，我想说选项 3 最有意义，特别是考虑到通过此选择，您可以从标准的“基于视图的应用程序”模板开始，只需添加有关图像视图的位即可剩下的就独自一人吧。不过，最后一个观察结果是选择 3；发送到窗口的 2 条消息；

 [self.window addSubview:myViewController.view];

 [self.window makeKeyAndVisible];

似乎超出了任何方法的范围。这可能只是复制和粘贴错误，但请注意它们应位于“didFinishLaunchingWithOptions:”内