Using a UIScrollView to change the alpha of an image

Question

My aim is to effectively use a UIScrollView as a UISlider.

I've managed to code a UISlider to change the alpha of an image however I want to code a scrollview to change the alpha of an image when it is scrolled.

I think I'm on the right lines by using the scroll views content offset to adjust alpha balances in the scroll view delegate but I just can't seem to get the code to work!

Any suggestions on how I can get do this?

Thanks

Please show some code, what you have tried, and where your code seems to fail. — n00bProgrammer

TonyMkenu TonyMkenu · Accepted Answer · 2014-10-28T12:48:02

Yes, you have right... use the scroll view offset to modify the alpha:

For example:

- (void)scrollViewDidScroll:(UIScrollView *)scrollView { 

    if(scrollView.contentOffset.y >= 0 && scrollView.contentOffset.y <= 150.0) {
        float percent = (scrollView.contentOffset.y / 150.0);
               self.imageView.alpha = percent;

    } else if (scrollView.contentOffset.y > 150.0){
        self.imageView.alpha = 1;

    } else if (scrollView.contentOffset.y < 0) {
       // do other ... ;
    }
}

here you have an example: https://dl.dropboxusercontent.com/u/19438780/ScrollView_alpha.zip

So... happy coding!

Using a UIScrollView to change the alpha of an image

1 Answers