NetNewsWire/iOS/Article/WebViewProvider.swift

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//
// WebViewProvider.swift
// NetNewsWire-iOS
//
// Created by Maurice Parker on 9/21/19.
// Copyright © 2019 Ranchero Software. All rights reserved.
//
import Foundation
import WebKit
/// WKWebView has an awful behavior of a flash to white on first load when in dark mode.
/// Keep a queue of WebViews where we've already done a trivial load so that by the time we need them in the UI, they're past the flash-to-shite part of their lifecycle.
class WebViewProvider: NSObject, WKNavigationDelegate {
static let shared = WebViewProvider()
let articleIconSchemeHandler = ArticleIconSchemeHandler()
private let minimumQueueDepth = 3
private let maximumQueueDepth = 6
private var queue: [WKWebView] = []
private var waitingForFirstLoad = true
private var waitingCompletionHandler: ((WKWebView) -> ())?
func dequeueWebView(completion: @escaping (WKWebView) -> ()) {
if waitingForFirstLoad {
waitingCompletionHandler = completion
} else {
completeRequest(completion: completion)
}
}
func enqueueWebView(_ webView: WKWebView) {
guard queue.count < maximumQueueDepth else {
return
}
webView.navigationDelegate = self
queue.insert(webView, at: 0)
webView.loadHTMLString(ArticleRenderer.page.html, baseURL: ArticleRenderer.page.baseURL)
}
// MARK: WKNavigationDelegate
func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
if waitingForFirstLoad {
waitingForFirstLoad = false
if let completion = waitingCompletionHandler {
completeRequest(completion: completion)
waitingCompletionHandler = nil
}
}
}
// MARK: Private
private override init() {
super.init()
replenishQueueIfNeeded()
}
private func replenishQueueIfNeeded() {
while queue.count < minimumQueueDepth {
let preferences = WKPreferences()
preferences.javaScriptCanOpenWindowsAutomatically = false
preferences.javaScriptEnabled = true
let configuration = WKWebViewConfiguration()
configuration.preferences = preferences
configuration.setValue(true, forKey: "allowUniversalAccessFromFileURLs")
configuration.allowsInlineMediaPlayback = true
configuration.mediaTypesRequiringUserActionForPlayback = .video
configuration.setURLSchemeHandler(articleIconSchemeHandler, forURLScheme: ArticleRenderer.imageIconScheme)
let webView = WKWebView(frame: .zero, configuration: configuration)
enqueueWebView(webView)
}
}
private func completeRequest(completion: @escaping (WKWebView) -> ()) {
if let webView = queue.popLast() {
webView.navigationDelegate = nil
replenishQueueIfNeeded()
completion(webView)
return
}
assertionFailure("Creating WKWebView in \(#function); queue has run dry.")
let webView = WKWebView(frame: .zero)
completion(webView)
}
}