Using Xcode, create a new View-based Application project and name it Animation.

Drag and drop an image named tennisball.jpg to the Resources folder in Xcode. When the Add dialog appears, select the Copy Item into Destination Group's Folder (If Needed) check box so that a copy of the image is copied into the project.

Double-click the AnimationViewController.xib file to edit it in Interface Builder.

In the View window, drag and drop an ImageView onto it and set its Image property to tennisball.jpg (see Figure 15-1).

Figure 15.1. Figure 15-1

Select the View (outside the ImageView) and change the background color to black (see Figure 15-2).

Figure 15.2. Figure 15-2

Add a Label and a Slider view from the Library onto the View window (see Figure 15-3). Set the Initial property of the Slider view to 0.01.

Figure 15.3. Figure 15-3

In the AnimationViewController.h file, declare the following outlets, actions, and fields:

#import <UIKit/UIKit.h>

@interface AnimationViewController : UIViewController {
    IBOutlet UIImageView *imageView;
    IBOutlet UISlider *slider;

    CGPoint position;
    NSTimer *timer;

    float ballRadius;
}

@property (nonatomic, retain) UIImageView *imageView;
@property (nonatomic, retain) UISlider *slider;

-(IBAction) sliderMoved:(id) sender;

@end

Back in Interface Builder, connect the outlets and actions as shown in Figure 15-4.

Figure 15.4. Figure 15-4

In the AnimationViewController.m file, add the following statements that appear in bold:

#import "AnimationViewController.h"

@implementation AnimationViewController

@synthesize imageView;
@synthesize slider;

-(void) onTimer {
    imageView.center = CGPointMake(
                       imageView.center.x + position.x,
                       imageView.center.y + position.y);

    if (imageView.center.x > 320 - ballRadius || imageView.center.x < ballRadius)
        position.x = -position.x;
    if (imageView.center.y > 460 - ballRadius || imageView.center.y < ballRadius)
        position.y = -position.y;
}

- (void)viewDidLoad {
    ballRadius = imageView.frame.size.width/2;
    [slider setShowValue:YES];

    position = CGPointMake(12.0,4.0);
    timer = [NSTimer scheduledTimerWithTimeInterval:slider.value
            target:self
            selector:@selector(onTimer)
            userInfo:nil
            repeats:YES];

    [super viewDidLoad];
}

-(IBAction) sliderMoved:(id) sender {
    [timer invalidate];
    timer = [NSTimer scheduledTimerWithTimeInterval:slider.value
            target:self
            selector:@selector(onTimer)
            userInfo:nil
            repeats:YES];
}

- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
}

- (void)dealloc {
    [timer invalidate];

[imageView release];
    [slider release];
    [super dealloc];
}

@end

Press Command-R to test the application on the iPhone Simulator. You should now see the tennis ball animating on the screen (see Figure 15-5). To vary the speed of the animation, move the slider. Moving the slider to the right slows down the animation; moving it to the left speeds it up.

Figure 15.5. Figure 15-5

Using Xcode, create a new View-based Application project and name it Animations2.

Add a series of images to the Resources folder by dragging and dropping them into the Resources folder in Xcode. When the Add dialog appears, select the Copy Item into Destination Group's Folder (If Needed) check box so that a copy of each of the images will be copied into the project. Figure 15-9 shows the images added.

Figure 15.9. Figure 15-9

In the Animations2ViewController.m file, add the following statements that appear in bold:

- (void)viewDidLoad {
    NSArray *images = [NSArray arrayWithObjects:
                          [UIImage imageNamed:@"MacSE.jpeg"],
                          [UIImage imageNamed:@"imac.jpeg"],
                          [UIImage imageNamed:@"MacPlus.jpg"],
                          [UIImage imageNamed:@"imac_old.jpeg"],
                          [UIImage imageNamed:@"Mac8100.jpeg"],
                          nil];

    CGRect frame = CGRectMake(0,0,320,460);
    UIImageView *imageView = [[UIImageView alloc] initWithFrame:frame];
    imageView.animationImages = images;
    imageView.contentMode = UIViewContentModeScaleAspectFit;
    imageView.animationDuration = 3;    //---seconds to complete one set
                                        // of animation---
    imageView.animationRepeatCount = 0; //---continuous---

    [imageView startAnimating];

    [self.view addSubview:imageView];
    [imageView release];
    [super viewDidLoad];
}

Press Command-R to test the series of images on the iPhone Simulator. The images are displayed in the ImageView view (see Figure 15-10), one at a time.

Figure 15.10. Figure 15-10