先用下面的方法生成一张渐变色图片
具体的渐变方向改CGContextDrawLinearGradient参数，或者用其他样式的渐变，例如CGContextDrawRadialGradient
- (UIImage *)createImageWithSize:(CGSize)imageSize gradientColors:(NSArray *)colors percentage:(CGFloat)percents {
NSMutableArray *ar = [NSMutableArray array];
for(UIColor *c in colors) {
[ar addObject:(id)c.CGColor];
}
UIGraphicsBeginImageContextWithOptions(imageSize, YES, 1);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSaveGState(context);
CGColorSpaceRef colorSpace = CGColorGetColorSpace([[colors lastObject] CGColor]);
CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (CFArrayRef)ar, &percents);
CGPoint start = CGPointMake(0.0, 0.0);
CGPoint end = CGPointMake(imageSize.width, imageSize.height);
CGContextDrawLinearGradient(context, gradient, start, end, kCGGradientDrawsBeforeStartLocation | kCGGradientDrawsAfterEndLocation);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
CGGradientRelease(gradient);
CGContextRestoreGState(context);
CGColorSpaceRelease(colorSpace);
UIGraphicsEndImageContext();
return image;
}
用UIColor的类方法把图片转为颜色
- (UIColor *)colorWithPatternImage:(UIImage *)image;
