Question

I’ve made a program that generates an image at a random x-coordinate at the top of the screen. The image then falls down to the bottom. However, I want to keep generating new images (of the same image) every few seconds so that it’s as though these duplicates of the same image are continually “raining” from the top.

How can I make all of this code repeat every 0.5 seconds?

@implementation ViewController {

    UIImageView *_myImage;

}

- (void)viewDidLoad
{
    srand(time(NULL));e
    int random_x_coordinate = rand() % 286;
    CGRect myImageRect = CGRectMake(random_x_coordinate, 0.0f, 40.0f, 40.0f);
    UIImageView *myImage = [[UIImageView alloc] initWithFrame:myImageRect];
    [myImage setImage:[UIImage imageNamed:@"flake.png"]];
    myImage.opaque = YES;
    [self.view addSubview:myImage];
    _myImage = myImage;


    //FALLING BIRDS TIMER
    moveObjectTimer = [NSTimer scheduledTimerWithTimeInterval:0.001 target:self selector:@selector(moveObject) userInfo:nil repeats:YES];


}
    //FALLING BIRDS MOVER
-(void) moveObject {        // + means down and the number next to it is how many pixels y moves down per each tick of the TIMER above
        _myImage.center = CGPointMake(_myImage.center.x, _myImage.center.y +1);
    }

Answer 1

Just put animation cycle inside the method you call on timer, something like

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:0.5
                                                      target:self
                                                    selector:@selector(animate)
                                                    userInfo:nil repeats:YES];
    [timer fire];
}

- (void)animate
{
    CGFloat hue = ( arc4random() % 256 / 256.0 );  //  0.0 to 1.0
    CGFloat saturation = ( arc4random() % 128 / 256.0 ) + 0.5;  //  0.5 to 1.0, away from white
    CGFloat brightness = ( arc4random() % 128 / 256.0 ) + 0.5;  //  0.5 to 1.0, away from black
    UIColor *color = [UIColor colorWithHue:hue saturation:saturation brightness:brightness alpha:1];

    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
    view.backgroundColor = color;
    [self.view addSubview:view];

    [UIView animateWithDuration:1.0 animations:^{
        view.frame = CGRectMake(0, 200, 50, 50);
    }];
}

Will give you squares dropping down from top, continuously. Just remember to clean up unused views regularly to avoid memory issues.