6

我正在使用水平 UIScrollView,并且我想要根据内容偏移的 x 值进行背景颜色转换。

示例: UIScrollView 的宽度为 640px。当内容偏移量等于 0px 时,背景颜色必须为红色。当内容偏移为 320 px 时,背景必须为黄色。但最重要的是,当 UIScrollview 在 0px 和 320px 之间时,背景颜色必须在红色和黄色之间。

提示:当您从搜索中向左滑动时,iOS 的 twitter 应用程序具有相同的动画。导航上的标签略微消失。

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3 回答 3

20

您需要根据偏移百分比创建颜色。

像这样在颜色之间创建转换的最简单方法是使用 HSB 颜色空间。

另外,这不是动画。“动画”效果由滚动视图提供给您。您只需要在每次滚动视图更改时设置颜色。

在委托方法中,您可以执行类似的操作。

编辑使其更灵活

// this just calculates the percentages now and passes it off to another method.
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    // vertical
    CGFloat maximumVerticalOffset = scrollView.contentSize.height - CGRectGetHeight(scrollView.frame);
    CGFloat currentVerticalOffset = scrollView.contentOffset.y;

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

    // percentages
    CGFloat percentageHorizontalOffset = currentHorizontalOffset / maximumHorizontalOffset;
    CGFloat percentageVerticalOffset = currentVerticalOffset / maximumVerticalOffset;

    [self scrollView:scrollView didScrollToPercentageOffset:CGPointMake(percentageHorizontalOffset, percentageVerticalOffset)];
}

// this just gets the percentage offset.
// 0,0 = no scroll
// 1,1 = maximum scroll
- (void)scrollView:(UIScrollView *)scrollView didScrollToPercentageOffset:(CGPoint)percentageOffset
{
    UIColor *HSBColor = [self HSBColorForOffsetPercentage:percentageOffset.x];

    UIColor *RGBColor = [self RGBColorForOffsetPercentage:percentageOffset.x];
}

// HSB color just using Hue
- (UIColor *)HSBColorForOffsetPercentage:(CGFloat)percentage
{
    CGFloat minColorHue = 0.0;
    CGFloat maxColorHue = 0.2; // this is a guess for the yellow hue.

    CGFloat actualHue = (maxColorHue - minColorHue) * percentage + minColorHue;

    // change these values to get the colours you want.
    // I find reducing the saturation to 0.8 ish gives nicer colours.
    return [UIColor colorWithHue:actualHue saturation:1.0 brightness:1.0 alpha:1.0];
}

// RGB color using all R, G, B values
- (UIColor *)RGBColorForOffsetPercentage:(CGFloat)percentage
{
    // RGB 1, 0, 0 = red
    CGFloat minColorRed = 1.0;
    CGFloat minColorGreen = 0.0;
    CGFloat minColorBlue = 0.0;

    // RGB 1, 1, 0 = yellow
    CGFloat maxColorRed = 1.0;
    CGFloat maxColorGreen = 1.0;
    CGFloat maxColorBlue = 0.0;

    // if you have specific beginning and end RGB values then set these to min and max respectively.
    // it should even work if the min value is greater than the max value.

    CGFloat actualRed = (maxColorRed - minColorRed) * percentage + minColorRed;
    CGFloat actualGreen = (maxColorGreen - minColorGreen) * percentage + minColorGreen;
    CGFloat actualBlue = (maxColorBlue - minColorBlue) * percentage + minColorBlue;

    return [UIColor colorWithRed:actualRed green:actualGreen blue:actualBlue alpha:1.0];
}

我不知道 RGB 方法将如何处理中间值。它可能会在中间变成棕色等......但你可以玩。

这应该让您了解如何使用滚动视图为任何东西设置动画作为控制它的一种方式。

使用这种方法,您可以控制不透明度、大小、旋转、字体大小等……您甚至可以组合多种事物(就像我对 RGB 所做的那样)。

于 2014-10-02T11:10:52.737 回答
1

受@Fogmeister 回答的启发,我迅速将这些部分拼凑在一起。

extension UIColor {
    static func color(between start: UIColor, and end: UIColor, percentage: CGFloat) -> UIColor {
        let startRGB = start.rgba
        let stopRGB = end.rgba

        let red: CGFloat = (stopRGB.red - startRGB.red) * percentage + startRGB.red
        let green: CGFloat = (stopRGB.green - startRGB.green) * percentage + startRGB.green
        let blue: CGFloat = (stopRGB.blue - startRGB.blue) * percentage + startRGB.blue
        let alpha: CGFloat = (stopRGB.alpha - startRGB.alpha) * percentage + startRGB.alpha

        return UIColor(red: red, green: green, blue: blue, alpha: alpha)
    }

    var rgba: (red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat) {
        var red: CGFloat = 0
        var green: CGFloat = 0
        var blue: CGFloat = 0
        var alpha: CGFloat = 0
        getRed(&red, green: &green, blue: &blue, alpha: &alpha)
        return (red, green, blue, alpha)
    }
}

现在您可以执行以下操作:

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    let offset = scrollView.contentOffset.y
    let scrolledDistance = offset + scrollView.contentInset.top
    let progress = max(0, min(1, scrolledDistance / scrollView.contentSize.height))

    someLabel.textColor = .color(between: .red, and: .green, percentage: progress)
}

警告:此实现将触发 swiftlints large_tuple规则。但是您可以禁用,只需将“- large_tuple”添加到disabled_rules部分。

于 2020-01-06T20:24:45.350 回答
-3

在你的 scrollView 委托中尝试这样的事情:

-(void)scrollViewDidScroll:(UIScrollView *)scrollView{
    CGPoint a = self.mainScrollView.contentOffset;
    if(a.x >= 320){
        [UIView animateWithDuration:0.5 animations:^{
            [self.view setBackgroundColor:[UIColor redColor]];
        }];
    }
    else{
        [UIView animateWithDuration:0.5 animations:^{
            [self.view setBackgroundColor:[UIColor yellowColor]];
        }];
    }
}
于 2014-10-02T10:59:28.323 回答