渐变

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#import "MyView.h"

#define RGBCOLOR(r,g,b,a) [UIColor colorWithRed:(r)/0.0f green:(g)/0.0f blue:(b)/0.0f alpha:a]

@implementation MyView

// Only override drawRect: if you perform custom drawing.

// An empty implementation adversely affects performance during animation.

- (void)drawRect:(CGRect)rect {

CGContextRef context = UIGraphicsGetCurrentContext();

CGContextSetRGBFillColor(context, 255, 255, 255, 1);

CGContextFillRect(context, CGRectMake(0, 0, self.frame.size.width, self.frame.size.height));

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

CGFloat alphaGradientLocations[] = {0, 1.0};

NSArray* alphaGridentColors = @[(id)RGBCOLOR(0, 0, 0, 0).CGColor,

(id)RGBCOLOR(0, 0, 0, 1).CGColor];

CGGradientRef alphaGradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef)alphaGridentColors, alphaGradientLocations);

CGContextDrawLinearGradient(context, alphaGradient, CGPointZero, CGPointMake(0, self.frame.size.height), 0);

CGGradientRelease(alphaGradient);

CGColorSpaceRelease(colorSpace);

}

@end

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