iOS为UIView的子类添加渐变颜色

+ (UIColor*) gradientFromColor:(UIColor*)c1 toColor:(UIColor*)c2 withWidth:(CGFloat)width andHeight:(CGFloat)height{
    CGSize size = CGSizeMake(width, height);
    UIGraphicsBeginImageContextWithOptions(size, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
    
    NSArray* colors = [NSArray arrayWithObjects:(id)c1.CGColor, (id)c2.CGColor, nil];
    CGGradientRef gradient = CGGradientCreateWithColors(colorspace, (CFArrayRef)colors, NULL);
    CGContextDrawLinearGradient(context, gradient, CGPointMake(0, 0), CGPointMake(size.width, size.height), 0);
    
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    
    CGGradientRelease(gradient);
    CGColorSpaceRelease(colorspace);
    UIGraphicsEndImageContext();
    
    return [UIColor colorWithPatternImage:image];
}