Question

I’m using a double for loop to add UIButtons to a UIScrollView in a grid format. These UIButtons take time to load as they have subviews that are UIImageViews which get their UIImages by downloading data off the internet.

Right now, the subviews don’t show until AFTER the method completely finishes executing. Correct me if I’m wrong, but I’m guessing xcode doesn’t show added subviews until a method is done executing.

However, I do want to show each subview getting added one at a time, as a cool loading effect. How would I implement this?

Thanks!

Answer 1

You should use multiple threads to load your pictures so that your main thread does not become sluggish. I recently wrote something similar…Take a look at my code from my viewWillAppear method:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    self.myImages = [self.myModel retrieveAttachments]; //Suppose this takes a long time
    for (UIImage *image in self.myImages) 
    {
        dispatch_async(dispatch_get_main_queue(), ^{
            [self addImageToScrollView:image animated:YES]; });
    }
}
});

The addImageToScrollView method would be like so:

-(void) addImageToScrollView: (UIImage *) image animated: (BOOL) animated
{
    //Create image view
    UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
    imageView.image = image;

    if(animated)
    {
        imageView.alpha = 0;
        [self.myScrollView addSubview:imageView];
        [UIView animateWithDuration:ADD_IMAGE_APPEARING_ANIMATION_SPEED animations:^{
            imageView.alpha = 1;
        }];
    }
    else
    {
        [self.myScrollView addSubview:imageView];
    }
}