在滚动过程中更改背景颜色 [英] Make background color change during scroll

问题描述

我的应用程序有一个入门部分，共有4页，用户可以水平滚动该页面以了解如何使用该应用程序(标准).我希望背景颜色随着用户在页面之间滚动而过渡.

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.

我有四个要使用的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，但是我不确定如何将其转到所选的特定颜色.

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. 任何实现都会迅速或客观地实现-c

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

谢谢

推荐答案

适用于任何有兴趣的人.这是解决方案.我结合了在堆栈上找到的一些答案，并将其修改为使用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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