背景信息：我有UIImageView。我通过以下方式在其图像上添加了叠加颜色：
UIGraphicsBeginImageContext(initialImage.size);
[initialImage drawInRect:CGRectMake(0, 0, initialImage.size.width, initialImage.size.height) blendMode:kCGBlendModeNormal alpha:alphaValue];
UIBezierPath * path = [UIBezierPath bezierPathWithRect:CGRectMake(0, 0, initialImage.size.width, initialImage.size.height)];
[overlayColor setFill];
[path fillWithBlendMode:kCGBlendModeMultiply alpha:1];
finalImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
[self setImage:finalImage];
我仍然希望将其添加为叠加颜色，但我希望它具有渐变效果。我一直试图找到一种方法来做到这一点，但并没有真正成功。我想，用渐变添加叠加颜色的方法是错误的？我不知道该怎么做。我尝试将CGGradientLayer作为sublayer添加到UIImageView，但它不起作用。
我考虑添加UIView并将backgroundColor设置为overlayColor，然后将CGGradientLayer添加为sublayer UIView它作为subview添加到UIImageView但是，我们不应该将subviews添加到UIImageViews。
有人可以帮我这个吗？也许我应该改变我的做法？
指出我正确的方向也会很棒！
如果这篇文章还不完全清楚的话，我期待你的回复和道歉！
提前感谢您的帮助！
修改：CGGradientLayer
CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = self.frame;
UIColor *colorOne = [UIColor colorFromHex:self.feedColor withAlpha:(alphaValue * 0.7)];
UIColor *colorTwo = [UIColor colorFromHex:self.feedColor withAlpha:(alphaValue * 1.0)];
gradient.colors = [NSArray arrayWithObjects:(id)colorOne.CGColor, (id)colorTwo.CGColor, nil];
[self.layer insertSublayer:gradient atIndex:0];
答案 0 :(得分：1)
我会使用Core Graphics来获取输入图像，对其应用渐变叠加，然后将其传递到UIImageView。这样的事情应该达到预期的效果：
- (UIImage *)imageWithGradientOverlay:(UIImage *)sourceImage color1:(UIColor *)color1 color2:(UIColor *)color2 gradPointA:(CGPoint)pointA gradPointB:(CGPoint)pointB {
CGSize size = sourceImage.size;
// Start context
UIGraphicsBeginImageContext(size);
CGContextRef c = UIGraphicsGetCurrentContext();
// Draw source image into context
CGContextDrawImage(c, (CGRect){CGPointZero, size}, sourceImage.CGImage);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGFloat gradLocs[] = {0, 1};
NSArray *colors = @[(id)color1.CGColor, (id)color2.CGColor];
// Create a simple linear gradient with the colors provided.
CGGradientRef grad = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef)colors, gradLocs);
CGColorSpaceRelease(colorSpace);
// Draw gradient with multiply blend mode over the source image
CGContextSetBlendMode(c, kCGBlendModeMultiply);
CGContextDrawLinearGradient(c, grad, pointA, pointB, 0);
CGGradientRelease(grad);
// Grab resulting image from context
UIImage *resultImg = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return resultImg;
}
这是sourceImage是输入图片的地方，color1和color2是您的渐变颜色，gradPointA和gradPointB是您的线性渐变终点（在Core Graphics坐标系中，左下角是（0,0））。
通过这种方式，您可以节省不得不使用图层。如果您经常使用不同的颜色重新绘制，那么您可能需要采用使用图层的方法。
答案 1 :(得分：1)
如果您正在寻找更具动态性的方法，那么我会继承CALayer而不是UIImageView。因此，你需要这样的东西：
@interface gradientImageLayer : CALayer
- (instancetype)initWithFrame:(CGRect)frame;
@end
@implementation gradientImageLayer
- (instancetype)initWithFrame:(CGRect)frame {
if (self = [super init]) {
self.opaque = YES; // Best for performance, but you if you want the layer to have transparency, then remove.
UIImage *i = [UIImage imageNamed:@"foo2.png"]; // Replace with your image
self.frame = frame;
self.contentsScale = [UIScreen mainScreen].nativeScale;
self.contents = (__bridge id _Nullable)(i.CGImage);
// Your code for the CAGradientLayer was indeed correct.
CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = frame;
// Add whatever colors you want here.
UIColor *colorOne = [UIColor colorWithRed:1 green:1 blue:0 alpha:0.1];
UIColor *colorTwo = [UIColor colorWithRed:0 green:1 blue:1 alpha:0.2];
gradient.colors = @[(id)colorOne.CGColor, (id)colorTwo.CGColor]; // Literals read far nicer than a clunky [NSArray arrayWith.... ]
[self addSublayer:gradient];
}
return self;
}
@end
此方法的缺点是您无法应用不同的混合模式。我在CALayer上应用混合模式的唯一解决方案是通过Core Graphics，但随后我的原始答案会更好。
答案 2 :(得分：0)
我将在此question
中发布协作解决方案此类别允许您使用任何混合模式（乘法，法线等）和CoreGraphics添加颜色叠加或渐变颜色叠加
快捷键4：
extension UIImage {
//creates a static image with a color of the requested size
static func fromColor(color: UIColor, size: CGSize) -> UIImage {
let rect = CGRect(x: 0, y: 0, width: size.width, height: size.height)
UIGraphicsBeginImageContext(rect.size)
let context = UIGraphicsGetCurrentContext()
context?.setFillColor(color.cgColor)
context?.fill(rect)
let img = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return img!
}
func blendWithColorAndRect(blendMode: CGBlendMode, color: UIColor, rect: CGRect) -> UIImage {
let imageColor = UIImage.fromColor(color: color, size:self.size)
let rectImage = CGRect(x: 0, y: 0, width: self.size.width, height: self.size.height)
UIGraphicsBeginImageContextWithOptions(self.size, true, 0)
let context = UIGraphicsGetCurrentContext()
// fill the background with white so that translucent colors get lighter
context!.setFillColor(UIColor.white.cgColor)
context!.fill(rectImage)
self.draw(in: rectImage, blendMode: .normal, alpha: 1)
imageColor.draw(in: rect, blendMode: blendMode, alpha: 0.8)
// grab the finished image and return it
let result = UIGraphicsGetImageFromCurrentImageContext()
//self.backgroundImageView.image = result
UIGraphicsEndImageContext()
return result!
}
//creates a static image with a gradient of colors of the requested size
static func fromGradient(colors: [UIColor], locations: [CGFloat], horizontal: Bool, size: CGSize) -> UIImage {
let rect = CGRect(x: 0, y: 0, width: size.width, height: size.height)
UIGraphicsBeginImageContext(rect.size)
let context = UIGraphicsGetCurrentContext()
let colorSpace = CGColorSpaceCreateDeviceRGB()
let cgColors = colors.map {$0.cgColor} as CFArray
let grad = CGGradient(colorsSpace: colorSpace, colors: cgColors , locations: locations)
let startPoint = CGPoint(x: 0, y: 0)
let endPoint = horizontal ? CGPoint(x: size.width, y: 0) : CGPoint(x: 0, y: size.height)
context?.drawLinearGradient(grad!, start: startPoint, end: endPoint, options: .drawsAfterEndLocation)
let img = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return img!
}
func blendWithGradientAndRect(blendMode: CGBlendMode, colors: [UIColor], locations: [CGFloat], horizontal: Bool = false, alpha: CGFloat = 1.0, rect: CGRect) -> UIImage {
let imageColor = UIImage.fromGradient(colors: colors, locations: locations, horizontal: horizontal, size: size)
let rectImage = CGRect(x: 0, y: 0, width: self.size.width, height: self.size.height)
UIGraphicsBeginImageContextWithOptions(self.size, true, 0)
let context = UIGraphicsGetCurrentContext()
// fill the background with white so that translucent colors get lighter
context!.setFillColor(UIColor.white.cgColor)
context!.fill(rectImage)
self.draw(in: rectImage, blendMode: .normal, alpha: 1)
imageColor.draw(in: rect, blendMode: blendMode, alpha: alpha)
// grab the finished image and return it
let result = UIGraphicsGetImageFromCurrentImageContext()
//self.backgroundImageView.image = result
UIGraphicsEndImageContext()
return result!
}
}
示例渐变：
let newImage = image.blendWithGradientAndRect(blendMode: .multiply,
colors: [.red, .white],
locations: [0, 1],
horizontal: true,
alpha: 0.8,
rect: imageRect)
单色示例：
let newImage = image.blendWithColorAndRect(blendMode: .multiply, color: .red, rect: imageRect)