我可以使用UIBezierPath在UITableView部分周围绘制阴影图像吗？

Question

I have a shadow image that I would like to draw around the outer edge of a grouped UITableView section. This is the image:

I can get the UIBezierPath that represents the rect I want to draw around, but I can't figure out how to repeat the image along the route of the rect. So far it just fills the rect with the image:

UIImage *patternImg = [UIImage imageNamed:@"cellShadow"];
UIColor *fill = [UIColor colorWithPatternImage:patternImg];
[fill setFill];
CGRect aSectRect = [self rectForSection:0];
UIBezierPath *aSectPath = [self createRoundedPath:aSectRect];
[aSectPath fill];

Is this possible? What do I need to do?

Answer 1

Unfortunately, there's no way to have UIBezierPath use an image as a "brush" which is essentially what you'd want. But you can have CoreGraphics draw a shadow for you:

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetShadow(context, CGSizeZero, myShadowRadius);
// Draw your shape here

Now if you draw just one shape it will get a shadow. But if you draw more shapes, each will get its own shadow which might not be what you want. The solution is called a transparency layer, which is not related to CALayers or something but is just some kind of "grouping" in CoreGraphics:

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetShadow(context, CGSizeZero, myShadowRadius);
CGContextBeginTransparencyLayer(context, NULL);
// Draw your shapes here.
CGContextEndTransparencyLayer(context);

Between the CGContextBeginTransparencyLayer and CGContextEndTransparencyLayer calls the shadow is disabled. After the CGContextEndTransparencyLayer call, the shadow is applied to everything that has been drawn between begin and end as if it were just one shape.