Make background color change during scroll

Question

I have an onboarding section of my app with 4 pages the users scrolls through horizontally to get an idea of how to use the app (standard). I want the background color to tr

Answer 1

For anyone interested. This is the solution. I combined some answers I found on stack and adapted it to use 4 colors

- (void)scrollViewDidScroll:(UIScrollView *)scrollView  {
CGFloat pageWidth = self.scrollView.frame.size.width;
float fractionalPage = self.scrollView.contentOffset.x / pageWidth;
NSInteger page = lround(fractionalPage);
self.pageControl.currentPage = page;

// horizontal
CGFloat maximumHorizontalOffset = scrollView.contentSize.width - CGRectGetWidth(scrollView.frame);
CGFloat currentHorizontalOffset = scrollView.contentOffset.x;

// percentages
CGFloat percentageHorizontalOffset = currentHorizontalOffset / maximumHorizontalOffset;

NSLog(@"content offfset: %f", percentageHorizontalOffset);

if (percentageHorizontalOffset < 0.333333) {
    self.view.backgroundColor = [self fadeFromColor:self.colorArray[0] toColor:self.colorArray[1] withPercentage:percentageHorizontalOffset*3];
} else if (percentageHorizontalOffset >= 0.333333 && percentageHorizontalOffset < 0.666667) {
    self.view.backgroundColor = [self fadeFromColor:self.colorArray[1] toColor:self.colorArray[2] withPercentage:(percentageHorizontalOffset-0.333333)*3];
} else if (percentageHorizontalOffset >= 0.666667) {
    self.view.backgroundColor = [self fadeFromColor:self.colorArray[2] toColor:self.colorArray[3] withPercentage:(percentageHorizontalOffset-0.666667)*3];
}
}

- (UIColor *)fadeFromColor:(UIColor *)fromColor toColor:(UIColor *)toColor withPercentage:(CGFloat)percentage
{
    // get the RGBA values from the colours
CGFloat fromRed, fromGreen, fromBlue, fromAlpha;
[fromColor getRed:&fromRed green:&fromGreen blue:&fromBlue alpha:&fromAlpha];

CGFloat toRed, toGreen, toBlue, toAlpha;
[toColor getRed:&toRed green:&toGreen blue:&toBlue alpha:&toAlpha];

//calculate the actual RGBA values of the fade colour
CGFloat red = (toRed - fromRed) * percentage + fromRed;
CGFloat green = (toGreen - fromGreen) * percentage + fromGreen;
CGFloat blue = (toBlue - fromBlue) * percentage + fromBlue;
CGFloat alpha = (toAlpha - fromAlpha) * percentage + fromAlpha;

// return the fade colour
return [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
}