Question

I’d like to create random images falling from the top of the screen, down to the bottom where they disappear. So far, I’ve been able to make 1 image fall down, at a fixed spawn point (center), but I’m unsure how to generate many more that spawn at random places on the top (somewhat like a snowfall or rainfall effect).

This is what I have so far:

-(void) viewDidLoad {
    moveObjectTimer = [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:@selector(moveObject) userInfo:nil repeats:YES]; }


-(void) moveObject {        // + means down and 5 is SPEED
    bird.center = CGPointMake(bird.center.x, bird.center.y +5); }

Answer 1

Say suppose you have 10 images in an array, then to select any 10 images at random you would do;

int randomIndex rand()/RAND_MAX * 10 + 1;

Then in some method, you could animate it as;

-(void) moveObject{
   int randomIndex = rand()/RAND_MAX * 10 + 1;
   UIImage *image = [self.myImages objectAtIndex:randomIndex];
   UIImageView *imageView = [[UIImageView alloc] initWithImage: image];
  CGRect mainRect = CGRectMake(view.frame.size.width + image.size.width,view.frame.size.height - image.size.height,image.frame.size.width,image.size.height );
    imageView.frame mainRect;
    [UIView animateWithDuration:0.5 delay:0 options:UIViewAnimationOptionCurveEaseIn animations:^{
        mainRect.frame.size.origin.x = 0;
        mainRect.frame.origin.y = 0;
        imageView.frame =mainRect;
    } completion:nil];
}

Your NSTimer should trigger this method and then this would select the random image out of your images, here I suppose 10 images that you have in an array. Then this would animate the images from outside the top/right corner to the bottom left corner at the specified time interval as specified with NSTimer.