ios – UIScrollview动画取决于内容偏移量

我正在使用水平UIScrollView,我想要一个背景颜色转换,具体取决于内容偏移的x值.

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.当内容偏移量为320像素时,背景必须为黄色.但最重要的是,当UIScrollview介于0px和320px之间时,背景颜色必须介于红色和黄色之间.

提示：当您从搜索向左滑动时,iOS的Twitter应用程序具有相同的动画.导航上的标签稍微消失.

解决方法

您需要根据偏移百分比创建颜色.

在这样的颜色之间创建切换的最简单方法是使用HSB颜色空间.

此外,这不是动画. “动画”效果由scrollview提供给您.您只需在每次滚动视图更改时设置颜色.

在委托方法中,你可以做这样的事情.

编辑以使更灵活

// 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 = 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方法将如何对中间值执行.它可能在中间变成棕色……但你可以玩.

这应该让您了解如何使用滚动视图来动画ANYTHING作为控制它的方法.

使用此方法,您可以控制不透明度,大小,旋转,字体大小等…您甚至可以组合多个内容(就像我使用RGB一样).