title: iOS: MaterialComponents shadow
body: <p>I want to use the <code>MaterialComponents</code> in my <code>Swift 4</code> to add shadow to my views but I can't understand how can I use the shadow elevator. I created a class named <code>ShadowedView</code> like the <a href="https://material.io/components/ios/catalog/shadows/shadow-elevations/" rel="nofollow noreferrer">documentation</a> with the same implementation, then in the xib I set the UIView subclass to <code>ShadowedView</code>. But the build failed with this error <code>Use of unresolved identifier 'MDCShadowLayer'</code>. The documentation is not clear for me. Can anyone please explain to me how can I use the <code>MaterialComponents</code>?</p>