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What's the difference between UIWebView and WKWebView?

Swift version: 5.0

Paul Hudson    @twostraws   

The UIWebView class has been around since iOS 2.0 as a way to show HTML content inside your app, but iOS 8.0 introduced WKWebView as an alternative - what's the difference?

Well, there are several differences, but two are particularly important. First, UIWebView is part of UIKit, and thus is available to your apps as standard. You don't need to import anything – it's just there. This also means it's available inside Interface Builder, so you can drag and drop web view into your designs.

Second, WKWebView is run in a separate process to your app so that it can draw on native Safari JavaScript optimizations. This means WKWebView loads web pages faster and more efficiently than UIWebView, and also doesn't have as much memory overhead for you.

In iOS 8.0 WKWebView was unable to load local files, but this got fixed in iOS 9.0. The main reason to use UIWebView nowadays is for access to older features such as "Scale pages to fit" - this is not available in WKWebView.

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Available from iOS 8.0 – see Hacking with Swift tutorial 4

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