This code snippet shows how to easily generate images at runtime for use in a button. This concept can be use in a variety of ways to reduce the amount of image assets need in an app.

SKCoreImage

// -- Create the button

testButton_ = [UIButton buttonWithType:UIButtonTypeCustom];
[testButton_ setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
testButton_.contentEdgeInsets = UIEdgeInsetsMake(10.0, 10.0, 10.0, 10.0);
[testButton_ setBackgroundImage:[self buttonImageExample] forState:UIControlStateNormal];
[testButton_ setTitle:@"Test Button" forState:UIControlStateNormal];
testButton_.translatesAutoresizingMaskIntoConstraints = NO;
[view addSubview:testButton_];

- (UIImage *)buttonImageExample
{
    // -- Setup a few sizes needed to generate the stretchable image
    CGSize imageSize = CGSizeMake(20.0, 20.0);
    CGFloat halfSize = ceilf(imageSize.width/2.0);
    
    // -- Start an image context, all drawing after this call will go to that context
    [UIImage beginImageContextWithSize:imageSize];
    
    // -- Start Custom Drawing Code
    
    CGRect drawRect = CGRectMake(0.0, 0.0, imageSize.width, imageSize.height);
    [UIView drawRect:drawRect withFillColor:[UIColor colorWithHex:0xff66CCFF]];
    
    CGRect insetRect = CGRectMake(1.0, 1.0, drawRect.size.width - 2.0, drawRect.size.height - 2.0);
    [UIView drawRect:insetRect withFillColor:[UIColor whiteColor]];
    
    CGPathRef clipPath = [UIView newPathWithRect:insetRect];
    [UIView startClipToPath:clipPath];
    
    CGRect gradientRect = CGRectMake(insetRect.origin.x, insetRect.origin.y, insetRect.size.width, 4.0);
    [UIView drawVerticalGradientWithStartColor:[UIColor colorWithHex:0x4466CCFF] endColor:[UIColor colorWithHex:0x0066CCFF] inRect:gradientRect];
    
    [UIView endClipToPath:clipPath];
    
    // -- End Custom Drawing Code
    
    // -- Setup insets to make the image stretchable.
    UIEdgeInsets stretchInsets = UIEdgeInsetsMake(imageSize.height - 5.0,
                                                  halfSize - 1.0,
                                                  imageSize.height - 3.0,
                                                  halfSize - 1.0);
    
    // -- End the image context and return the resulting image.
    // -- This image can be stored so as to only create the asset once.
    return [[UIImage endImageContext]
            resizableImageWithCapInsets:stretchInsets
            resizingMode:UIImageResizingModeStretch];
}