wkwebview in production

WKWebView in Production 7 things you should know about

Jeremy WiebeSenior Engineer, Lead

In the beginning there was UIWebView

What is UIWebView?• Original web rendering component

introduced in iOS 2.0 • This is what was historically used to build out

hybrid apps or load any web content inside an iOS app

Remember this?

UIWebView !== Safari• Mobile Safari tends to load pages 2-3x faster

than a UIWebView • Changes and fixes applied to Safari often not

ported into UIWebView • UIWebview is clunky, crashy, leaks memory • Scrolling blocks images loading and animation • Different JavaScript engine than Safari (not Nitro)

Why does UIWebView not have Nitro?

Nitro is excluded because Apple wanted to make hybrid apps less performant and force everybody to use their native platform

Excluded due to security reasons. Running a Just-In-Time compiler requires marking pages in RAM as executable - iOS does not allow this out of security concerns (except in Safari)

Cynical Answer Real Answer

Introducing WKWebView

WKWebView

Introduced in iOS 8 to give developers a performant webview (“same” performance as Safari)

WKWebView's rendering is all done in a separate process owned by the WKWebView

WKWebView == WebKit

Benefits of WKWebView

Better HTML 5 Support

WKWebView also gives us…• Significant performance gains in WebGL

applications (though supported in UIWebview) • Less "crashy" behaviour when rendering bugs

are triggered from HTML/CSS/JavaScript

More benefits!• Faster JavaScript and page rendering (thanks Nitro!) • 60fps interactive scrolling • Better communication between Swift and JS

(we haven’t experimented with this yet) • Since we are sharing the JS engine with

Safari, WKWebView should be better maintained and more reliable

How do I implement WKWebView?

• Don’t worry, there’s a ton of great documentation!


• Don’t worry, there’s a ton of great documentation!

• What was formerly a single class (UIWebView) and protocol (UIWebViewDelegate) is now 14 classes and 3 protocols (WKNavigationDelegate, WKScriptMessageHandler, WKUIDelegate)

• Other than class docs (and StackOverflow), no official “How-To WKWebView” from Apple

WKWebView Related ClassesWKBackForwardList WKBackForwardListItem WKFrameInfo WKNavigation WKNavigationAction WKNavigationResponse WKPreferences WKProcessPool WKScriptMessage

WKSecurityOrigin WKUserContentController WKUserScript WKWebViewConfiguration WKWebsiteDataRecord WKWebsiteDataStore WKWindowFeatures WKWebView

More code required• Automatically handled by UIWebView

• App store links

• JS alerts, confirms, inputs

• Sharing cookies between web views

The 7 Wonders Disappointments of

WKWebView

(and what to do about them)

Cannot load bundled content in iOS 8

#1

Cannot load bundled content

• Critical to many apps • UIWebView:

• webView!.loadRequest(request)


• High-level: copy the files we need to load into a /tmp directory that we can load files from

• Alternative: serve files we need from a web server in the app

• Solution: Fixed in iOS 9

Cannot intercept POST requests

#2

Cannot intercept POST requests• POST bodies are missing in NSURLRequest

sent to delegate methods • Solution: for now leave it -- in line with

Android behaviour • Good news: WebKit forums indicate this is a

bug and there seems to be a bit of traction

Broken UI state preservation

#3

No state preservation participation

• WKWebView doesn’t conform to the state preservation API (no restorationIdentifier)

• In Astro its used to reduce memory footprint and prevent crashes

• Solution: build our own by saving the last known URL

WSOD: White Screen of Death

#4

• Seeing some webviews display about:blank for no reason upon navigating back

• Appears to be a memory issue

WSOD: White Screen of Death

WSOD - Our Solution

We poll each webview that we manage and not currently visible (in the view hierarchy)

Views Appear Halfway Down

#5

• Happens when the frame is not set before load completes http://www.openradar.me/22855188

• Had to get creative on this one. • Turns out, duplicate <head> tags are ignored… • … so we create a <head> tag at the beginning JUST

to scroll back up

Views Appear Halfway Down

http://www.openradar.me/22855188

Our Solution

View Doesn’t Render Until Visible

#6

View Doesn’t Render Until Visible

• Big problem for preloading tabs in a tab bar layout

• Bigger problem if you rely on Javascript to run in those webviews

• Solution is an off-screen “holding pen” for web views not currently visible

Our Solution

Broken or Self-Signed Certs in iOS 8

#7

WKWebView and Certs• Bug in WKWebView where the documented

way of doing custom analysis of SSL certificates is broken

• webView(_:didReceiveAuthenticationChallenge:completionHandler:) is never called

• Important for internal use • No workaround

Other Weird Bugs

Need to know about these:• When app is sent to background, JS stops executing in ~10sec

while native code (and JS in UIWebView) keeps running for ~3 min until completely suspended by OS.

• Unlike UIWebView, the webView.URL property is updated to the navigation target the first delegate method is called by WKWebView.

• App store links don’t work by default -- have to intercept requests (http://atmarkplant.com/ios-wkwebview-tips/#applink)

http://atmarkplant.com/ios-wkwebview-tips/#applink

Are others using it?

Who uses WKWebView?

WKWebView is enabled by default in our hybrid app SDK

astro.mobify.com

Jeremy Wiebe

wkwebview in production

Technology