Frosted Glass Effect
An added flourish to the custom alert is a newly introduced visual effect found in iOS 7 and highlighted in the Control Center—the frosted glass appearance. Apple provides this effect by default in a number of UIKit elements: UITabBar, UINavigationBar, and UIToolbar.
Outside the embedded implementation in these bars, no mechanism is available to include this effect in your own views. Apple has provided sample code, a UIImage category, that simulates this effect. Unfortunately, it pales in comparison to the built-in implementation. The category is only a close approximation, and worse, is much slower than the embedded version, rendering it unusable as a live effect.
To work around this limitation, Recipe 3-4 subclasses a ...
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