Modern technique of adding gradient to UIView

 

I know of several ways of adding background gradients to UIView. I was wondering what is the most efficient and scalable way of doing so, and why? Here are the techniques I've used:

  • Create subview of UIView and overwrite the drawRect, where I draw the gradient in current context.

    a. When using the above gradient create it with the bounds of view I want to decorate and insert this background gradient as first subview, ie – insertSubview:atIndex:

    b. After I get the background gradient view from above, I render it in image context and use it as background image, ie 

    UIGraphicsBeginImageContext(gradView.bounds.size);
[gradView.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *gradientImg = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIColor *background = [UIColor colorWithPatternImage:gradientImg];
self.view.backgroundColor = background;

  • Create stretchable PNG and use that to decorate view background. Technique is very similar to the way you decorate UIButton. 

    -(UIColor *)backgroundColor:(CGRect)frame
{
    UIImage *bg = [UIImage imageNamed:@"background_23x36"];
    bg = [bg resizableImageWithCapInsets:UIEdgeInsetsMake(0.0, 11.0, 0.0, 11.0)];
    UIGraphicsBeginImageContextWithOptions(frame.size, YES, [[UIScreen mainScreen] scale]);
    [bg drawInRect:frame];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return [UIColor colorWithPatternImage:image];
}

  • Create subview of UIView but instead of overwriting the drawRect, use CAGradientLayer. Similar to http://nscookbook.com/2013/04/recipe-20-using-cagradient-layer-in-a-custom-view/

    • So what is most efficient and scalable way to add gradient as a background?

    正如Fogmeister上面所建议的，在你的UIView子类的drawRect:方法中执行它。 

    - (void)drawRect:(CGRect)rect
{
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = UIGraphicsGetCurrentContext();

    NSArray *gradientColors = [NSArray arrayWithObjects:(id) [UIColor redColor].CGColor, [UIColor yellowColor].CGColor, nil];

    CGFloat gradientLocations[] = {0, 0.50, 1};
    CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef) gradientColors, gradientLocations);

    CGPoint startPoint = CGPointMake(CGRectGetMidX(rect), CGRectGetMinY(rect));
    CGPoint endPoint = CGPointMake(CGRectGetMidX(rect), CGRectGetMaxY(rect));

    CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0);
    CGGradientRelease(gradient);
    CGColorSpaceRelease(colorSpace);
}

    DrawRect is the more efficient way i think. I'd like to extend jverrijt's nice answer. If you need alpha components (transparent to black gradient fe), then you can use this: 

    UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO, 0.0);
CGContextSaveGState(UIGraphicsGetCurrentContext());
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);
CGContextRestoreGState(UIGraphicsGetCurrentContext());

//Draw stuffs

UIGraphicsEndImageContext();
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