Question

I’m reading the documentation about gradients and I’m a little bit lost.
I have a view, and inside that view, I just want to draw a simple black to gray linear gradient inside a rect (smaller than the view), from bottom to top.
How may I do that without subclassing anything (I’ve read many things that need to subclass the view)?

I’m searching a way to do this as simple as I’ve ever done on various platforms. Something like (language free 🙂 ) :

blackcolor = MakeBlack();
whiteColor = MakeWhite();

startPoint = MakeStartPoint();
endPoint = MakeEndPoint();

onthisgraphicport = SetGraphicPort(self.view);
clippingRect = MakeClipRect();

DrawGradient(from:whiteColor, to:blackcolor, from:startPoint, to:endPoint, onthisgraphicport, intoThisRect:clippingRect);

Thank you for your help.

Answer 1

This code snippet might help. I found the code some time ago on the web. Unfortunately, I forgot the site, so not sure whom to give credit.

The code as is draws a white to black gradient. Just change the rect and the colors to your needs.

@interface MyView : UIView {
    CGGradientRef _gradientRef;
}

@end

@implementation MyView

- (void) dealloc
{
    [super dealloc];
}

- (id) initWithFrame:(CGRect)frame {
    if ((self = [super initWithFrame:frame])) {
        CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB();
        CGFloat colors[] =
        {
            1.0f, 1.0f, 1.0f, 1.0f,
            0.0f, 0.0f, 0.0f, 1.0f,
        };
        _gradientRef = CGGradientCreateWithColorComponents(rgb, colors, NULL, sizeof(colors) / (sizeof(colors[0]) * 4));
        CGColorSpaceRelease(rgb);
    }

    return self;
}

- (void) drawRect:(CGRect)rect {
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGPoint start = rect.origin;
    start.y = 0;
    CGPoint end = CGPointMake(rect.origin.x, rect.size.height);
    CGContextDrawLinearGradient(context, _gradientRef, start, end, kCGGradientDrawsBeforeStartLocation | kCGGradientDrawsAfterEndLocation);

    [super drawRect:rect];
}

@end