为UIView添加褪色和透明度

Question

我知道如何制作和动画像一个在谈到与iOS新应用程序商店应用程序的共享子图的图6+(见附件截图),但我不知道如何添加漂亮的透明度着色效果在这个观点上.任何人都可以提供代码示例,使其UIView看起来与截图中的完全相同？

PS alphaUIView独有的属性不做这样的事情.

Answer 1

您可以将此方法添加到UIView类别,并根据需要重用.它将"theColor"中的线性黑色渐变应用于给定视图的透明度.

您应该在项目中使用QuartzCore.framework以使用CAGradientLayer对象.

+ (void)addLinearGradientToView:(UIView *)theView withColor:(UIColor *)theColor transparentToOpaque:(BOOL)transparentToOpaque
{
    CAGradientLayer *gradient = [CAGradientLayer layer];

    //the gradient layer must be positioned at the origin of the view
    CGRect gradientFrame = theView.frame;
    gradientFrame.origin.x = 0;
    gradientFrame.origin.y = 0;
    gradient.frame = gradientFrame;

    //build the colors array for the gradient
    NSArray *colors = [NSArray arrayWithObjects:
                       (id)[theColor CGColor],
                       (id)[[theColor colorWithAlphaComponent:0.9f] CGColor],
                       (id)[[theColor colorWithAlphaComponent:0.6f] CGColor],
                       (id)[[theColor colorWithAlphaComponent:0.4f] CGColor],
                       (id)[[theColor colorWithAlphaComponent:0.3f] CGColor],
                       (id)[[theColor colorWithAlphaComponent:0.1f] CGColor],
                       (id)[[UIColor clearColor] CGColor],
                       nil];

    //reverse the color array if needed
    if(transparentToOpaque)
    {
       colors = [[colors reverseObjectEnumerator] allObjects];
    }

    //apply the colors and the gradient to the view
    gradient.colors = colors;

    [theView.layer insertSublayer:gradient atIndex:0];
}

请注意,您应该将View的backgroundColor设置为clearColor,以便它不会干扰渐变.此外,对于屏幕截图中显示的结果,transparentToOpaque标志应为YES.

Answer 2

如果有人需要,PedroSilva的解决方案可以转换为Swift(也可以添加垂直选项)

class func addLinearGradientToView(view: UIView, colour: UIColor, transparntToOpaque: Bool, vertical: Bool)
{
    let gradient = CAGradientLayer()
    let gradientFrame = CGRectMake(0, 0, view.frame.size.width, view.frame.size.height)
    gradient.frame = gradientFrame

    var colours = [
        colour.CGColor,
        colour.colorWithAlphaComponent(0.9).CGColor,
        colour.colorWithAlphaComponent(0.8).CGColor,
        colour.colorWithAlphaComponent(0.7).CGColor,
        colour.colorWithAlphaComponent(0.6).CGColor,
        colour.colorWithAlphaComponent(0.5).CGColor,
        colour.colorWithAlphaComponent(0.4).CGColor,
        colour.colorWithAlphaComponent(0.3).CGColor,
        colour.colorWithAlphaComponent(0.2).CGColor,
        colour.colorWithAlphaComponent(0.1).CGColor,
        UIColor.clearColor().CGColor
    ]

    if transparntToOpaque == true
    {
        colours = colours.reverse()
    }

    if vertical == true
    {
        gradient.startPoint = CGPointMake(0, 0.5)
        gradient.endPoint = CGPointMake(1, 0.5)
    }
    gradient.colors = colours
    view.layer.insertSublayer(gradient, atIndex: 0)
}