Visual Effects - iOS Core Animation - page 50

Layer Borders
Another useful pair of CALayer properties are borderWidth and borderColor .
Together these define a line that is drawn around the edge of the layer. This line (known as
a stroke ) follows the bounds of the layer, including the corner curvature.
The borderWidth is a floating-point number that defines the stroke thickness in points.
This defaults to zero (no border). The borderColor defines the color of the stroke and
defaults to black.
The type of borderColor is CGColorRef , not UIColor , so it's not a Cocoa object
per-se. However, you should be aware that the layer retains the borderColor , even
though there's no indication of this from the property declaration. CGColorRef behaves
like an NSObject in terms of retain/release, but the Objective-C syntax does not provide a
way to indicate this, so even strongly retained CGColorRef properties must be declared
using assign .
The border is drawn inside the layer bounds, and in front of any other layer contents,
including sublayers. If we modify the example to include a layer border (see Listing 4.2),
you can see how this works (see Figure 4.3).
Listing 4.2 Applying a Border
@implementation ViewController
- ( void )viewDidLoad
{
[ super viewDidLoad ];
//set the corner radius on our layers
self . layerView1 . layer . cornerRadius = 20.0f ;
self . layerView2 . layer . cornerRadius = 20.0f ;
//add a border to our layers
self . layerView1 . layer . borderWidth = 5.0f ;
self . layerView2 . layer . borderWidth = 5.0f ;
//enable clipping on the second layer
self . layerView2 . layer . masksToBounds = YES ;
}
@end