89 lines
2.3 KiB
Swift
89 lines
2.3 KiB
Swift
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//
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// DetailViewControllerWebViewProvider.swift
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// NetNewsWire-iOS
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//
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// Created by Maurice Parker on 9/21/19.
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// Copyright © 2019 Ranchero Software. All rights reserved.
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//
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import Foundation
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import WebKit
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/// WKWebView has an awful behavior of a flash to white on first load when in dark mode.
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/// 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.
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class DetailViewControllerWebViewProvider: NSObject, WKNavigationDelegate {
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static let shared = DetailViewControllerWebViewProvider()
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private let minimumQueueDepth = 3
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private let maximumQueueDepth = 6
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private var queue: [WKWebView] = []
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private var waitingForFirstLoad = true
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private var waitingCompletionHandler: ((WKWebView) -> ())?
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func dequeueWebView(completion: @escaping (WKWebView) -> ()) {
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if waitingForFirstLoad {
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waitingCompletionHandler = completion
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} else {
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completeRequest(completion: completion)
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}
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}
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func enqueueWebView(_ webView: WKWebView) {
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guard queue.count < maximumQueueDepth else {
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return
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}
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webView.navigationDelegate = self
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queue.insert(webView, at: 0)
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let pageURL = Bundle.main.url(forResource: "page", withExtension: "html")!
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let page = try! String(contentsOf: pageURL)
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let baseURL = pageURL.deletingLastPathComponent()
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webView.loadHTMLString(page, baseURL: baseURL)
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}
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// MARK: WKNavigationDelegate
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func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
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if waitingForFirstLoad {
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waitingForFirstLoad = false
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if let completion = waitingCompletionHandler {
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completeRequest(completion: completion)
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waitingCompletionHandler = nil
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}
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}
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}
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// MARK: Private
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private override init() {
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super.init()
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replenishQueueIfNeeded()
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}
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private func replenishQueueIfNeeded() {
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while queue.count < minimumQueueDepth {
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let webView = WKWebView(frame: .zero)
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enqueueWebView(webView)
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}
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}
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private func completeRequest(completion: @escaping (WKWebView) -> ()) {
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if let webView = queue.popLast() {
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webView.navigationDelegate = nil
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replenishQueueIfNeeded()
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completion(webView)
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return
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}
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assertionFailure("Creating WKWebView in \(#function); queue has run dry.")
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let webView = WKWebView(frame: .zero)
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completion(webView)
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}
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}
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