在滚动期间更改背景颜色

Make background color change during scroll(在滚动期间更改背景颜色)

问题描述

我的应用有一个入门部分，其中包含 4 个页面，用户可以水平滚动以了解如何使用该应用(标准).我希望当用户从一个页面滚动到另一个页面时背景颜色会发生变化.

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 transition as the user scrolls from page to page.

我想要使用 4 个 RGB 值:

I have the 4 RGB values I want to use:

241,170,170

241,170,170

170,201,241

170,201,241

188,170,241

188,170,241

241,199,170

241,199,170

我知道我必须使用滚动视图委托 + 内容偏移来更改 uicolor 值，但我不确定如何让它转到我选择的特定颜色.

I know I must use the scroll view delegate + content offset to change the uicolor values, but im not sure how I get it to go to the specific colors ive selected.

任何帮助将不胜感激.任何实现都可以，快速或客观-c

Any help would be greatly appreciated. Any implementation would do, swift or objective-c

谢谢

推荐答案

对于任何有兴趣的人.这就是解决方案.我结合了我在堆栈上找到的一些答案并将其调整为使用 4 种颜色

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];
}    

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