Question

I have the following UIView custom class:

@implementation BackgroundView

- (void)drawRect:(CGRect)rect 
{

    CGContextRef currentContext = UIGraphicsGetCurrentContext();

    CGGradientRef glossGradient;
    CGColorSpaceRef rgbColorspace;
    size_t num_locations = 2;
    CGFloat locations[2] = { 0.0, 1.0 };

    float r = (255.0)/(255.0);
    float g = (165.0)/(255.0);
    float b = (0.0)/(255.0);

    float rr = (238.0)/(255.0);
    float gg = (118.0)/(255.0);
    float bb = (0.0)/(255.0);

    CGFloat components[8] = { r, g, b, 1.0,  // Start color
        rr, gg, bb, 1.0 }; // End color

    rgbColorspace = CGColorSpaceCreateDeviceRGB();
    glossGradient = CGGradientCreateWithColorComponents(rgbColorspace, components, locations, num_locations);

    CGRect currentBounds = self.bounds;
    CGPoint topCenter = CGPointMake(CGRectGetMidX(currentBounds), 0.0f);
    CGPoint midCenter = CGPointMake(CGRectGetMidX(currentBounds), CGRectGetMidY(currentBounds));
    CGContextDrawLinearGradient(currentContext, glossGradient, topCenter, midCenter, 0);

    CGGradientRelease(glossGradient);
    CGColorSpaceRelease(rgbColorspace); 
}


@end

Basically, it’s supposed to make an orange gradient. The values “r”, “g”, and “b” are for a light orange, and the values “rr”, “gg”, “bb” are for a dark orange. But it doesn’t work. Only the top of the frame is orange, and the bottom of the frame is black. I can’t seem to get rid of the black.

What values would I use for an orange nice gradient. Can someone please look for mistakes? I can’t find any. Thanks so much!

Answer 1

That’s because you specify that the end point for your gradient is in middle of the currentBounds – see this line:

CGPoint midCenter = CGPointMake(CGRectGetMidX(currentBounds), CGRectGetMidY(currentBounds));

To get rid of the black make sure the y coordinate is at the bottom of your view.

Alternatively, you could use this code to extend your gradient after the end point

 CGContextDrawLinearGradient(currentContext, glossGradient, topCenter, midCenter, kCGGradientDrawsAfterEndLocation);