引擎盖下的网络浏览器的工作历史

Question

我正在尝试在 iOS 上为 WKWebView 实现我自己的 Web 浏览器历史记录，但我无法完全实现此功能，并且每次遇到麻烦。 我可以创建用户所在的历史，然后在历史中前后移动。 但是我遇到了下一个麻烦，我认为这只是我遇到的许多问题之一。 当我有例如 10 个元素的历史记录，然后我回到第 5 个元素，然后不要前进但尝试打开新链接，我无法删除元素 6-10 并放置新链接。

我认为我的问题是我无法完全理解历史在所有浏览器中的工作原理，这不是一项艰巨的任务，但我对这个算法感到困惑。 我保存历史的主要数据结构 帮助我了解如何在浏览器中使用此算法，或者是否存在一个很好的理论？

Answer 1

我已经解决了这个问题并很好地实现了完整的算法，完成的项目在这里：https://github.com/IhorYachmenov/Custom-browser-history-for-WKWebView。

算法：

struct PlayerHistory {
    
    static var shared = PlayerHistory()
    
    var historyExist: Bool = false
    var historyCurrentPosition: Int = 0
    var historyLastPositionBeforeUpdatingHistory: Int!
    var userHistoryKey: String!
    
    var backPressed: Bool!
    var forwardPressed: Bool!
    
    var urlOfPlayer: String!
    
    // Function only for first loading inside <viewDidLoad or another method from app LifeCycle>.
    mutating func getUrlForFirstLoading(initURL: String, key: String) -> String {
        
        urlOfPlayer = initURL
        
        guard HistoryStorage.shared.getHistoryFromUserDefaults() != nil else {
            updateFirstElement(key: key, url: initURL)
            return initURL
        }
        
        guard HistoryStorage.shared.getHistoryFromUserDefaults()![key] != nil else {
            return initURL
        }
        
        let position = HistoryStorage.shared.getHistoryFromUserDefaults()![key]!.count - 1
        
        historyExist = true
        historyCurrentPosition = position
        userHistoryKey = key
        let initUrlFromHistoryStorage = HistoryStorage.shared.getHistoryFromUserDefaults()![key]!.last!.url
        
        return initUrlFromHistoryStorage
    }
    
    // Create new or update exist history, use this method indsede <decidePolicyForNavigation>.
    mutating func updatePlayerHistory(backlisk: [String], key: String) {
        
        var history = [WebViewHistory]()
        
        for i in backlisk {
            history.append(WebViewHistory(i))
        }
        
        if (historyExist == true) {
            // If old history exist need compound both and then to save.
            
            let oldHistory = HistoryStorage.shared.getHistoryFromUserDefaults()![key]

            let oldAndNewHostoryTogether = oldHistory! + history
            
            var keyValuePair = Dictionary<String, [WebViewHistory]>()
            keyValuePair.updateValue(oldAndNewHostoryTogether, forKey: key)
            
            HistoryStorage.shared.removeHistory()
            HistoryStorage.shared.saveHistory(keyValuePair)
            
            setCurrentPosition(url: backlisk.last!, key: key)
        } else {
            var keyValuePair = Dictionary<String, [WebViewHistory]>()
            keyValuePair.updateValue(history, forKey: key)
            
            historyExist = true
            
            HistoryStorage.shared.removeHistory()
            HistoryStorage.shared.saveHistory(keyValuePair)
            setCurrentPosition(url: backlisk.last!, key: key)
        }
    }
        
    
    // Before using this method check if result don't equals nil. Use this method for navigation beetween history
    func moveThroughHistory(key: String, direction: Bool) -> String? {
        
        guard  historyExist != false else {
            return nil
        }
        
        let history = HistoryStorage.shared.getHistoryFromUserDefaults()![key]!
        
        if (direction == true) {
            let index = historyCurrentPosition + 1
            guard index != history.count else { return nil }
            return history[index].url
        } else {
            let index = historyCurrentPosition - 1
            guard index > 0 else { return history[0].url }
            return history[index].url
        }
        
        
    }
    
    // Method <setCurrentPosition> each time set position at history
    mutating func setCurrentPosition(url: String, key: String) {
        
        guard HistoryStorage.shared.getHistoryFromUserDefaults() != nil else { return }
        guard HistoryStorage.shared.getHistoryFromUserDefaults()![key] != nil else { return }
        
        let history = HistoryStorage.shared.getHistoryFromUserDefaults()![key]
        let index = history?.firstIndex(of: WebViewHistory(url))
        
        guard index != nil else {
            historyCurrentPosition = 0
            return
        }
        historyCurrentPosition = index!
    }
    
    // <removeUnusedPeaceOfHistory> need use when user want open new page staying inside the middle of history
    mutating func removeUnusedPeaceOfHistory(key: String) {
        
        guard HistoryStorage.shared.getHistoryFromUserDefaults() != nil else {
            return
        }
        
        guard HistoryStorage.shared.getHistoryFromUserDefaults()![key] != nil else {
            return
        }
        
        var history = HistoryStorage.shared.getHistoryFromUserDefaults()![key]!
        let startIndex = historyCurrentPosition + 1
        let endIndex = history.endIndex - 1
        let countOfAllElements = history.count
        
        guard startIndex != countOfAllElements else { return }
        let range = startIndex...endIndex
        history.removeSubrange(range)
        
        var keyValuePair = Dictionary<String, [WebViewHistory]>()
        keyValuePair.updateValue(history, forKey: key)
        
        HistoryStorage.shared.removeHistory()
        HistoryStorage.shared.saveHistory(keyValuePair)
    }
        
    // Use <updateFirstElement> inside <getUrlForFirstLoading> if history doesn't exist
    private mutating func updateFirstElement(key: String, url: String) {
        var history = [WebViewHistory]()
        history.insert(WebViewHistory(url), at: 0)
        
        var keyValuePair = Dictionary<String, [WebViewHistory]>()
        keyValuePair.updateValue(history, forKey: key)
        
        HistoryStorage.shared.saveHistory(keyValuePair)
        historyExist = true
        historyCurrentPosition = 0
        
    }
    
    // Use <webViewWillBeClosedSaveHistory> when WKWebView should be closed, if the user moves through history new position will be saved.
    mutating func webViewWillBeClosedSaveHistory(key: String) {
        let history = HistoryStorage.shared.getHistoryFromUserDefaults()![key]!
        let currentPosition = historyCurrentPosition + 1
        guard currentPosition != history.count else { return }
        removeUnusedPeaceOfHistory(key: key)
    }
}