ios 如何向 UIView 添加径向渐变？

How do I add a radial gradient to a UIView?

提问by Andrew

I have a UIViewwhich I want to have a radial gradient, and I'm wondering how to go about doing this?

我有一个UIView我想要一个径向渐变，我想知道如何去做这个？

采纳答案by John Gallagher

To do this you need to drop down to Core Graphics and use CGContextDrawRadialGradient.

为此，您需要下拉到 Core Graphics 并使用CGContextDrawRadialGradient。

Similar Stack Overflow Questions

类似的堆栈溢出问题

How can I draw a sector with radial gradient (iphone)

如何绘制具有径向渐变的扇区（iphone）

How to draw a gradient line (fading in/out) with Core Graphics/iPhone?

如何使用 Core Graphics/iPhone 绘制渐变线（淡入/淡出）？

Other Resources

其他资源

There's a tutorial showing how to draw icons with gradients on iOS here:

有一个教程展示了如何在 iOS 上绘制带有渐变的图标：

http://redartisan.com/2011/05/13/porting-iconapp-core-graphics

http://redartisan.com/2011/05/13/porting-iconapp-core-graphics

He's put the code on Github, complete with a UIView subclass that shows the (rather longwinded) way of making gradients using Core Graphics:

他将代码放在 Github 上，并附带一个 UIView 子类，该子类显示了使用 Core Graphics 制作渐变的（相当冗长的）方式：

https://github.com/crafterm/IconApp/blob/master/IconApp/IconView.m

https://github.com/crafterm/IconApp/blob/master/IconApp/IconView.m

回答by Karlis

First subclass a UIView:

第一个子类化 UIView：

@implementation UIRadialView

- (void)drawRect:(CGRect)rect
{
    // Setup view
    CGFloat colorComponents[] = {0.0, 0.0, 0.0, 1.0,   // First color:  R, G, B, ALPHA (currently opaque black)
                                 0.0, 0.0, 0.0, 0.0};  // Second color: R, G, B, ALPHA (currently transparent black)
    CGFloat locations[] = {0, 1}; // {0, 1) -> from center to outer edges, {1, 0} -> from outer edges to center
    CGFloat radius = MIN((self.bounds.size.height / 2), (self.bounds.size.width / 2));
    CGPoint center = CGPointMake(self.bounds.size.width / 2, self.bounds.size.height / 2);

    // Prepare a context and create a color space
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSaveGState(context);
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    // Create gradient object from our color space, color components and locations
    CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace, colorComponents, locations, 2);

    // Draw a gradient
    CGContextDrawRadialGradient(context, gradient, center, 0.0, center, radius, 0);
    CGContextRestoreGState(context);

    // Release objects
    CGColorSpaceRelease(colorSpace);
    CGGradientRelease(gradient);
}

@end

And then add it to your view:

然后将其添加到您的视图中：

UIRadialView *radialView = [[UIRadialView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
radialView.backgroundColor = [UIColor redColor];
[self.view addSubview:radialView];

Result:

结果：

回答by Mark Moeykens

Swift 3 - @IBDesignable

Swift 3 - @IBDesignable

I worked off Karlis and Alexander's answers. I aimed to simplify as much as possible. Such as removing color space and locations (nil) so the gradient uses the defaults.

我解决了卡利斯和亚历山大的答案。我的目标是尽可能地简化。例如删除颜色空间和位置 ( nil) 以便渐变使用默认值。

How to Use

如何使用

Step 1

第1步

Create file and add this code: import UIKit

创建文件并添加以下代码：import UIKit

@IBDesignable
class RadialGradientView: UIView {

    @IBInspectable var InsideColor: UIColor = UIColor.clear
    @IBInspectable var OutsideColor: UIColor = UIColor.clear

    override func draw(_ rect: CGRect) {
        let colors = [InsideColor.cgColor, OutsideColor.cgColor] as CFArray
        let endRadius = min(frame.width, frame.height) / 2
        let center = CGPoint(x: bounds.size.width / 2, y: bounds.size.height / 2)
        let gradient = CGGradient(colorsSpace: nil, colors: colors, locations: nil)
        UIGraphicsGetCurrentContext()!.drawRadialGradient(gradient!, startCenter: center, startRadius: 0.0, endCenter: center, endRadius: endRadius, options: CGGradientDrawingOptions.drawsBeforeStartLocation)
    }
}

Step 2

第2步

On Storyboard, set the UIView to the above RadialGradientViewin Identity Inspector:

在 Storyboard 上，RadialGradientView在 Identity Inspector中将 UIView 设置为上述内容：

Step 3

第 3 步

Set the Inside Color and Outside Color for your gradient in Attributes Inspector and see the change on your Storyboard:

在属性检查器中为您的渐变设置内部颜色和外部颜色，然后查看故事板上的更改：

(Note: I made the UIView on the Storyboard big enough to so it fills the entire

（注意：我在 Storyboard 上制作了足够大的 UIView，因此它填满了整个

回答by Alexander

Here's Karlis' answer in Swift 3:

这是卡利斯在 Swift 3 中的回答：

override func draw(_ rect: CGRect) {

    // Setup view
    let colors = [UIColor.white.cgColor, UIColor.black.cgColor] as CFArray
    let locations = [ 0.0, 1.0 ] as [CGFloat]
    let radius = min((self.bounds.size.height / 2), (self.bounds.size.width / 2))
    let center = CGPoint.init(x: self.bounds.size.width / 2, y: self.bounds.size.height / 2)

    // Prepare a context and create a color space
    let context = UIGraphicsGetCurrentContext()
    context!.saveGState()
    let colorSpace = CGColorSpaceCreateDeviceRGB()

    // Create gradient object from our color space, color components and locations
    let gradient = CGGradient.init(colorsSpace: colorSpace, colors: colors, locations: locations)

    // Draw a gradient
    context!.drawRadialGradient(gradient!, startCenter: center, startRadius: 0.0, endCenter: center, endRadius: radius, options: CGGradientDrawingOptions(rawValue: 0))
    context?.restoreGState()
}

回答by c.lamont.dev

Here's Karlis answer in c# for Xamarin.iOS. Here I am specifying the colors directly but you can of course implement it the same way Karlis did.

这是 Xamarin.iOS 在 c# 中的 Karlis 答案。在这里，我直接指定颜色，但您当然可以像 Karlis 那样实现它。

public class RadialView : UIView
{
    public RadialView(CGRect rect) : base (rect)
    {
        this.BackgroundColor = UIColor.DarkGray;
    }

    public override void Draw(CGRect rect)
    {
        CGColor[] colorComponents = { UIColor.DarkGray.CGColor, UIColor.LightGray.CGColor };
        var locations = new nfloat[]{ 1, 0 }; 
        var radius = this.Bounds.Size.Height / 2;
        CGPoint center = new CGPoint(this.Bounds.Size.Width / 2, this.Bounds.Size.Height / 2);

        var context = UIGraphics.GetCurrentContext();
        context.SaveState();
        var colorSpace = CGColorSpace.CreateDeviceRGB();

        CGGradient gradient = new CGGradient(colorSpace, colorComponents, locations);
        context.DrawRadialGradient(gradient, center, 0, center, radius, CGGradientDrawingOptions.None);

        context.RestoreState();
        colorSpace.Dispose();
        gradient.Dispose();
    }
}