Question

正如标题所说，我试图给一些UIImageViews一个淡出效果，因为它们越来越接近我的UIScrollView的四个边缘中的任何一个。由于用户可以拖动UIImages，如果他将它们拖向边缘，它们会开始淡出，而不是像UIScrollView的边框那样给出剪切效果。我试过这个教程：

http://www.cocoanetics.com/2011/08/adding-fading-gradients-to-uitableview/

建议在另一个堆栈溢出问题，但它只能应用于UITableViews。我希望图像在离边界一厘米处时开始褪色。

Answer 1

与您链接到的Cocoanetics帖子中的内容类似，您可以创建CAGradientLayer来覆盖滚动视图。使用滚动视图的背景颜色（在我的示例中为白色）使其淡出到左，右，上和下边缘：

   CGColorRef innerColor = [UIColor colorWithWhite:1.0 alpha:0.0].CGColor;
   CGColorRef outerColor = [UIColor colorWithWhite:1.0 alpha:1.0].CGColor;

   // first, define a horizontal gradient (left/right edges)
   CAGradientLayer* hMaskLayer = [CAGradientLayer layer];
   hMaskLayer.opacity = .7;
   hMaskLayer.colors = [NSArray arrayWithObjects:(id)outerColor,
                        (id)innerColor, (id)innerColor, (id)outerColor, nil];
   hMaskLayer.locations = [NSArray arrayWithObjects:[NSNumber numberWithFloat:0.0],
                           [NSNumber numberWithFloat:0.15],
                           [NSNumber numberWithFloat:0.85],
                           [NSNumber numberWithFloat:1.0], nil];
   hMaskLayer.startPoint = CGPointMake(0, 0.5);
   hMaskLayer.endPoint = CGPointMake(1.0, 0.5);
   hMaskLayer.bounds = self.scrollView.bounds;
   hMaskLayer.anchorPoint = CGPointZero;

   CAGradientLayer* vMaskLayer = [CAGradientLayer layer];
   // without specifying startPoint and endPoint, we get a vertical gradient
   vMaskLayer.opacity = hMaskLayer.opacity;
   vMaskLayer.colors = hMaskLayer.colors;
   vMaskLayer.locations = hMaskLayer.locations;
   vMaskLayer.bounds = self.scrollView.bounds;
   vMaskLayer.anchorPoint = CGPointZero;

   // you must add the masks to the root view, not the scrollView, otherwise
   //  the masks will move as the user scrolls!
   [self.view.layer addSublayer: hMaskLayer];
   [self.view.layer addSublayer: vMaskLayer];

免责声明：这会使四角处的渐变/渐变倍增。您可以查看结果并确定它们是否足够好。如果没有，您还可以尝试在Photoshop之类的地方绘制透明图像，并使用您绘制的图像在顶部添加UIImageView子视图作为蒙版。

enter image description here

Youtube screen capture

Answer 2

Nate答案的Swift版本，但仅限于顶部和底部：

        let innerColor = UIColor(white: 1.0, alpha: 0.0).CGColor
        let outerColor = UIColor(white: 1.0, alpha: 1.0).CGColor;

        // define a vertical gradient (up/bottom edges)
        let colors = [outerColor, innerColor,innerColor,outerColor]
        let locations = [0.0, 0.15,0.85,1.0]

        var vMaskLayer : CAGradientLayer = CAGradientLayer()// layer];
        // without specifying startPoint and endPoint, we get a vertical gradient
        vMaskLayer.opacity = 0.7
        vMaskLayer.colors = colors;
        vMaskLayer.locations = locations;
        vMaskLayer.bounds = self.scrollView.bounds;
        vMaskLayer.anchorPoint = CGPointZero;

        // you must add the mask to the root view, not the scrollView, otherwise
        //  the masks will move as the user scrolls!
        self.view.layer.addSublayer(vMaskLayer)

Answer 3

这里有关于这个问题的几个帖子：

Changing the alpha inside UIScrollView

setting Alpha for UIView that is a subview of UIScrollVIew very slow

以及一些示例代码：

https://gist.github.com/MaximKeegan/2478842

如果你想按自己的方式去，那么首先得到UIScrollView的可见部分：

Getting the visible rect of an UIScrollView's content

然后淡化UIView：

UIView border with fade or blur effect

淡出任何接近UIScrollView边缘的内容

3 个答案: