SwiftyJSON 性能问题答案

【问题标题】：SwiftyJSON Performance IssuesSwiftyJSON 性能问题
【发布时间】：2015-05-28 22:00:14
【问题描述】：

我在使用 SwiftyJson 从我们的 API 解析 JSON 并填充核心数据时遇到严重的性能问题。

使用 Alamofire 下载数据，效果很好，但使用 SwiftyJson 解析 JSON 速度非常慢。为了查看库是否真的是问题所在，我在解析数据的众多地方之一重写了 json 解析。在下面的代码中，我正在解析大约 400 个旅游景点之一的开放时间。

查看这些屏幕截图中的差异，从 7.7 秒到 185 毫秒：

快捷方式：

    let openDescription:String = json["OpeningHours"]["OpeningHoursGenericExceptions"].string!
    let monOpen:[String]    = json["OpeningHours"]["Monday"]["From"].string!.componentsSeparatedByString(":")
    let monClose:[String]   = json["OpeningHours"]["Monday"]["To"].string!.componentsSeparatedByString(":")
    let tueOpen:[String]    = json["OpeningHours"]["Tuesday"]["From"].string!.componentsSeparatedByString(":")
    let tueClose:[String]   = json["OpeningHours"]["Tuesday"]["To"].string!.componentsSeparatedByString(":")
    let wedOpen:[String]    = json["OpeningHours"]["Wednesday"]["From"].string!.componentsSeparatedByString(":")
    let wedClose:[String]   = json["OpeningHours"]["Wednesday"]["To"].string!.componentsSeparatedByString(":")
    let thuOpen:[String]    = json["OpeningHours"]["Thursday"]["From"].string!.componentsSeparatedByString(":")
    let thuClose:[String]   = json["OpeningHours"]["Thursday"]["To"].string!.componentsSeparatedByString(":")
    let friOpen:[String]    = json["OpeningHours"]["Friday"]["From"].string!.componentsSeparatedByString(":")
    let friClose:[String]   = json["OpeningHours"]["Friday"]["To"].string!.componentsSeparatedByString(":")
    let satOpen:[String]    = json["OpeningHours"]["Saturday"]["From"].string!.componentsSeparatedByString(":")
    let satClose:[String]   = json["OpeningHours"]["Saturday"]["To"].string!.componentsSeparatedByString(":")
    let sunOpen:[String]    = json["OpeningHours"]["Sunday"]["From"].string!.componentsSeparatedByString(":")
    let sunClose:[String]   = json["OpeningHours"]["Sunday"]["To"].string!.componentsSeparatedByString(":")

原生方式：

    var monOpen:[String] = []
    var monClose:[String] = []
    var tueOpen:[String] = []
    var tueClose:[String] = []
    var wedOpen:[String] = []
    var wedClose:[String] = []
    var thuOpen:[String] = []
    var thuClose:[String] = []
    var friOpen:[String] = []
    var friClose:[String] = []
    var satOpen:[String] = []
    var satClose:[String] = []
    var sunOpen:[String] = []
    var sunClose:[String] = []
    var openDescription:String = ""
    
    if let attractionsArray = orgJson as? NSArray{
        if let attraction = attractionsArray[0] as? NSDictionary{
            if let openHours = attraction["OpeningHours"] as? NSDictionary{
                if let day = openHours["Monday"] as? NSDictionary{
                    if let open = day["From"] as? String{
                        monOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"] as? String{
                        monClose = close.componentsSeparatedByString(":")
                    }
                }
                if let day = openHours["Tuesday"] as? NSDictionary{
                    if let open = day["From"] as? String{
                        tueOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"] as? String{
                        tueClose = close.componentsSeparatedByString(":")
                    }
                }
                if let day = openHours["Wednesday"] as? NSDictionary{
                    if let open = day["From"] as? String{
                        wedOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"] as? String{
                        wedClose = close.componentsSeparatedByString(":")
                    }
                }
                if let day = openHours["Thursday"] as? NSDictionary{
                    if let open = day["From"] as? String{
                        thuOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"] as? String{
                        thuClose = close.componentsSeparatedByString(":")
                    }
                }
                if let day = openHours["Friday"] as? NSDictionary{
                    if let open = day["From"] as? String{
                        friOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"] as? String{
                        friClose = close.componentsSeparatedByString(":")
                    }
                }
                if let day = openHours["Saturday"] as? NSDictionary{
                    if let open = day["From"] as? String{
                        satOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"] as? String{
                        satClose = close.componentsSeparatedByString(":")
                    }
                }
                if let day = openHours["Sunday"] as? NSDictionary{
                    if let open = day["From"] as? String{
                        sunOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"] as? String{
                        sunClose = close.componentsSeparatedByString(":")
                    }
                }
                if let desc = openHours["OpeningHoursGenericExceptions"] as? String{
                    openDescription = desc
                }
            }
        }
    }

这只是正在解析的数据的一部分，因此在应用程序中性能非常明显。

我想问题是，我是否错误地使用了 SwiftyJSON 或者这是意料之中的？

【问题讨论】：

标签： ios json swift swifty-json

【解决方案1】：

首先，你的“native way”不等同于“Swifty way”。

SwiftyJSON 版本有 45 个 subscript 访问，而原生方式只有 23 个 subscript 访问。

要使“native way”等效，它应该是这样的：

let openDescription = attraction["OpeningHours"]!["OpeningHoursGenericExceptions"] as String
let monOpen  = (attraction["OpeningHours"]!["Monday"]!!["From"] as String).componentsSeparatedByString(":")
let monClose = (attraction["OpeningHours"]!["Monday"]!!["To"] as String).componentsSeparatedByString(":")
let tueOpen  = (attraction["OpeningHours"]!["Tuesday"]!!["From"] as String).componentsSeparatedByString(":")
let tueClose = (attraction["OpeningHours"]!["Tuesday"]!!["To"]! as String).componentsSeparatedByString(":")
// ...

或“Swifty way”应该是这样的：

let openHours = json[0]["OpeningHours"]
var day:JSON

day = openHours["Monday"]
if let open = day["From"].string {
    monOpen = open.componentsSeparatedByString(":")
}
if let close = day["To"].string {
    monClose = close.componentsSeparatedByString(":")
}
day = openHours["Tuesday"]
if let open = day["From"].string {
    tueOpen = open.componentsSeparatedByString(":")
}
if let close = day["To"].string {
    tueClose = close.componentsSeparatedByString(":")
}
// ...

无论如何，是的，SwiftyJSON 很慢。让我们测量一下：

import Foundation
import XCTest

let orgJson:AnyObject = [
    [
        "OpeningHours": [
            "OpeningHoursGenericExceptions": "test",
            "Monday":    ["From":"1:2:3","To":"1:2:3"],
            "Tuesday":   ["From":"1:2:3","To":"1:2:3"],
            "Wednesday": ["From":"1:2:3","To":"1:2:3"],
            "Thursday":  ["From":"1:2:3","To":"1:2:3"],
            "Friday":    ["From":"1:2:3","To":"1:2:3"],
            "Saturday":  ["From":"1:2:3","To":"1:2:3"],
            "Sunday":    ["From":"1:2:3","To":"1:2:3"],
        ]
    ]
]
let json = JSON(orgJson)

class JSONTestTests: XCTestCase {

    func testNativeSubscript() {
        measureBlock { () -> Void in

            for _ in 0 ..< 400 {
                autoreleasepool {
                    if let attraction = orgJson[0] as? NSDictionary {
                        let openDescription = attraction["OpeningHours"]!["OpeningHoursGenericExceptions"] as String
                        let monOpen  = (attraction["OpeningHours"]!["Monday"]!!["From"] as String).componentsSeparatedByString(":")
                        let monClose = (attraction["OpeningHours"]!["Monday"]!!["To"] as String).componentsSeparatedByString(":")
                        let tueOpen  = (attraction["OpeningHours"]!["Tuesday"]!!["From"] as String).componentsSeparatedByString(":")
                        let tueClose = (attraction["OpeningHours"]!["Tuesday"]!!["To"] as String).componentsSeparatedByString(":")
                        let wedOpen  = (attraction["OpeningHours"]!["Wednesday"]!!["From"] as String).componentsSeparatedByString(":")
                        let wedClose = (attraction["OpeningHours"]!["Wednesday"]!!["To"] as String).componentsSeparatedByString(":")
                        let thuOpen  = (attraction["OpeningHours"]!["Thursday"]!!["From"] as String).componentsSeparatedByString(":")
                        let thuClose = (attraction["OpeningHours"]!["Thursday"]!!["To"] as String).componentsSeparatedByString(":")
                        let friOpen  = (attraction["OpeningHours"]!["Friday"]!!["From"] as String).componentsSeparatedByString(":")
                        let friClose = (attraction["OpeningHours"]!["Friday"]!!["To"] as String).componentsSeparatedByString(":")
                        let satOpen  = (attraction["OpeningHours"]!["Saturday"]!!["From"] as String).componentsSeparatedByString(":")
                        let satClose = (attraction["OpeningHours"]!["Saturday"]!!["To"] as String).componentsSeparatedByString(":")
                        let sunOpen  = (attraction["OpeningHours"]!["Sunday"]!!["From"] as String).componentsSeparatedByString(":")
                        let sunClose = (attraction["OpeningHours"]!["Sunday"]!!["To"] as String).componentsSeparatedByString(":")
                        XCTAssertEqual(monOpen, ["1","2","3"], "")
                        XCTAssertEqual(openDescription, "test")
                    }
                }
            }
        }
    }

    func testJSONSubscript() {
        measureBlock { () -> Void in
            for _ in 0 ..< 400 {
                autoreleasepool {
                    let attraction = json[0]
                    let openDescription:String = attraction["OpeningHours"]["OpeningHoursGenericExceptions"].string!
                    let monOpen:[String]    = attraction["OpeningHours"]["Monday"]["From"].string!.componentsSeparatedByString(":")
                    let monClose:[String]   = attraction["OpeningHours"]["Monday"]["To"].string!.componentsSeparatedByString(":")
                    let tueOpen:[String]    = attraction["OpeningHours"]["Tuesday"]["From"].string!.componentsSeparatedByString(":")
                    let tueClose:[String]   = attraction["OpeningHours"]["Tuesday"]["To"].string!.componentsSeparatedByString(":")
                    let wedOpen:[String]    = attraction["OpeningHours"]["Wednesday"]["From"].string!.componentsSeparatedByString(":")
                    let wedClose:[String]   = attraction["OpeningHours"]["Wednesday"]["To"].string!.componentsSeparatedByString(":")
                    let thuOpen:[String]    = attraction["OpeningHours"]["Thursday"]["From"].string!.componentsSeparatedByString(":")
                    let thuClose:[String]   = attraction["OpeningHours"]["Thursday"]["To"].string!.componentsSeparatedByString(":")
                    let friOpen:[String]    = attraction["OpeningHours"]["Friday"]["From"].string!.componentsSeparatedByString(":")
                    let friClose:[String]   = attraction["OpeningHours"]["Friday"]["To"].string!.componentsSeparatedByString(":")
                    let satOpen:[String]    = attraction["OpeningHours"]["Saturday"]["From"].string!.componentsSeparatedByString(":")
                    let satClose:[String]   = attraction["OpeningHours"]["Saturday"]["To"].string!.componentsSeparatedByString(":")
                    let sunOpen:[String]    = attraction["OpeningHours"]["Sunday"]["From"].string!.componentsSeparatedByString(":")
                    let sunClose:[String]   = attraction["OpeningHours"]["Sunday"]["To"].string!.componentsSeparatedByString(":")
                    XCTAssertEqual(monOpen, ["1","2","3"], "")
                }
            }
        }
    }

    func testNativeBinding() {
        measureBlock { () -> Void in
            for _ in 0 ..< 400 {
                autoreleasepool {
                    var monOpen:[String] = []
                    var monClose:[String] = []
                    var tueOpen:[String] = []
                    var tueClose:[String] = []
                    var wedOpen:[String] = []
                    var wedClose:[String] = []
                    var thuOpen:[String] = []
                    var thuClose:[String] = []
                    var friOpen:[String] = []
                    var friClose:[String] = []
                    var satOpen:[String] = []
                    var satClose:[String] = []
                    var sunOpen:[String] = []
                    var sunClose:[String] = []
                    var openDescription:String = ""

                    if let attractionsArray = orgJson as? NSArray{
                        if let attraction = attractionsArray[0] as? NSDictionary{
                            if let openHours = attraction["OpeningHours"] as? NSDictionary{
                                if let day = openHours["Monday"] as? NSDictionary{
                                    if let open = day["From"] as? String{
                                        monOpen = open.componentsSeparatedByString(":")
                                    }
                                    if let close = day["To"] as? String{
                                        monClose = close.componentsSeparatedByString(":")
                                    }
                                }
                                if let day = openHours["Tuesday"] as? NSDictionary{
                                    if let open = day["From"] as? String{
                                        tueOpen = open.componentsSeparatedByString(":")
                                    }
                                    if let close = day["To"] as? String{
                                        tueClose = close.componentsSeparatedByString(":")
                                    }
                                }
                                if let day = openHours["Wednesday"] as? NSDictionary{
                                    if let open = day["From"] as? String{
                                        wedOpen = open.componentsSeparatedByString(":")
                                    }
                                    if let close = day["To"] as? String{
                                        wedClose = close.componentsSeparatedByString(":")
                                    }
                                }
                                if let day = openHours["Thursday"] as? NSDictionary{
                                    if let open = day["From"] as? String{
                                        thuOpen = open.componentsSeparatedByString(":")
                                    }
                                    if let close = day["To"] as? String{
                                        thuClose = close.componentsSeparatedByString(":")
                                    }
                                }
                                if let day = openHours["Friday"] as? NSDictionary{
                                    if let open = day["From"] as? String{
                                        friOpen = open.componentsSeparatedByString(":")
                                    }
                                    if let close = day["To"] as? String{
                                        friClose = close.componentsSeparatedByString(":")
                                    }
                                }
                                if let day = openHours["Saturday"] as? NSDictionary{
                                    if let open = day["From"] as? String{
                                        satOpen = open.componentsSeparatedByString(":")
                                    }
                                    if let close = day["To"] as? String{
                                        satClose = close.componentsSeparatedByString(":")
                                    }
                                }
                                if let day = openHours["Sunday"] as? NSDictionary{
                                    if let open = day["From"] as? String{
                                        sunOpen = open.componentsSeparatedByString(":")
                                    }
                                    if let close = day["To"] as? String{
                                        sunClose = close.componentsSeparatedByString(":")
                                    }
                                }
                                if let desc = openHours["OpeningHoursGenericExceptions"] as? String{
                                    openDescription = desc
                                }
                            }
                        }
                    }
                    XCTAssertEqual(monOpen, ["1","2","3"], "")
                }
            }
        }
    }
    func testJSONBinding() {
        measureBlock { () -> Void in
            for _ in 0 ..< 400 {
                autoreleasepool {
                    var monOpen:[String] = []
                    var monClose:[String] = []
                    var tueOpen:[String] = []
                    var tueClose:[String] = []
                    var wedOpen:[String] = []
                    var wedClose:[String] = []
                    var thuOpen:[String] = []
                    var thuClose:[String] = []
                    var friOpen:[String] = []
                    var friClose:[String] = []
                    var satOpen:[String] = []
                    var satClose:[String] = []
                    var sunOpen:[String] = []
                    var sunClose:[String] = []
                    var openDescription:String = ""

                    let openHours = json[0]["OpeningHours"]
                    var day:JSON

                    day = openHours["Monday"]
                    if let open = day["From"].string {
                        monOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"].string {
                        monClose
                            = close.componentsSeparatedByString(":")
                    }
                    day = openHours["Tuesday"]
                    if let open = day["From"].string {
                        tueOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"].string {
                        tueClose = close.componentsSeparatedByString(":")
                    }
                    day = openHours["WednesDay"]
                    if let open = day["From"].string {
                        wedOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"].string {
                        wedClose = close.componentsSeparatedByString(":")
                    }
                    day = openHours["Thursday"]
                    if let open = day["From"].string {
                        thuOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"].string {
                        thuClose = close.componentsSeparatedByString(":")
                    }
                    day = openHours["Friday"]
                    if let open = day["From"].string {
                        friOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"].string {
                        friClose = close.componentsSeparatedByString(":")
                    }
                    day = openHours["Saturday"]
                    if let open = day["From"].string {
                        satOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"].string {
                        satClose = close.componentsSeparatedByString(":")
                    }
                    day = openHours["Sunday"]
                    if let open = day["From"].string {
                        sunOpen = open.componentsSeparatedByString(":")
                    }
                    if let close = day["To"].string {
                        sunClose = close.componentsSeparatedByString(":")
                    }
                    XCTAssertEqual(monOpen, ["1","2","3"], "")
                }
            }
        }
    }

}

输出：

<unknown>:0: Test Case '-[JSONTestTests.JSONTestTests testJSONBinding]' measured [Time, seconds] average: 0.804, relative standard deviation: 5.592%, values: [0.835687, 0.814827, 0.819685, 0.841900, 0.764961, 0.845202, 0.691442, 0.779255, 0.818213, 0.830698], performanceMetricID:com.apple.XCTPerformanceMetric_WallClockTime, baselineName: "", baselineAverage: , maxPercentRegression: 10.000%, maxPercentRelativeStandardDeviation: 10.000%, maxRegression: 0.100, maxStandardDeviation: 0.100
<unknown>:0: Test Case '-[JSONTestTests.JSONTestTests testJSONSubscript]' measured [Time, seconds] average: 4.247, relative standard deviation: 3.496%, values: [4.019640, 4.004123, 4.146146, 4.194535, 4.487171, 4.300971, 4.310613, 4.408405, 4.318354, 4.279362], performanceMetricID:com.apple.XCTPerformanceMetric_WallClockTime, baselineName: "", baselineAverage: , maxPercentRegression: 10.000%, maxPercentRelativeStandardDeviation: 10.000%, maxRegression: 0.100, maxStandardDeviation: 0.100
<unknown>:0: Test Case '-[JSONTestTests.JSONTestTests testNativeBinding]' measured [Time, seconds] average: 0.223, relative standard deviation: 2.773%, values: [0.221099, 0.227395, 0.218860, 0.225989, 0.227128, 0.222370, 0.229956, 0.214535, 0.210818, 0.229868], performanceMetricID:com.apple.XCTPerformanceMetric_WallClockTime, baselineName: "", baselineAverage: , maxPercentRegression: 10.000%, maxPercentRelativeStandardDeviation: 10.000%, maxRegression: 0.100, maxStandardDeviation: 0.100
<unknown>:0: Test Case '-[JSONTestTests.JSONTestTests testNativeSubscript]' measured [Time, seconds] average: 0.362, relative standard deviation: 17.528%, values: [0.346285, 0.316185, 0.333650, 0.339416, 0.330243, 0.354034, 0.378730, 0.269519, 0.486904, 0.467607], performanceMetricID:com.apple.XCTPerformanceMetric_WallClockTime, baselineName: "", baselineAverage: , maxPercentRegression: 10.000%, maxPercentRelativeStandardDeviation: 10.000%, maxRegression: 0.100, maxStandardDeviation: 0.100

你的 SwiftyJSON：4.247
你的母语：0.223
我的 SwiftyJSON：0.804
我的母语：0.362

顺便说一句，如果我是你，我会这样做：

if let hours = orgJson[0]?["OpeningHours"] as? NSDictionary {
    let openDescription = hours["OpeningHoursGenericExceptions"] as? String ?? ""
    let monOpen  = hours["Monday"]?["From"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let monClose = hours["Monday"]?["To"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let tueOpen  = hours["Tuesday"]?["From"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let tueClose = hours["Tuesday"]?["To"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let wedOpen  = hours["Wednesday"]?["From"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let wedClose = hours["Wednesday"]?["To"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let thuOpen  = hours["Thursday"]?["From"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let thuClose = hours["Thursday"]?["To"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let friOpen  = hours["Friday"]?["From"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let friClose = hours["Friday"]?["To"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let satOpen  = hours["Saturday"]?["From"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let satClose = hours["Saturday"]?["To"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let sunOpen  = hours["Sunday"]?["From"]??.componentsSeparatedByString?(":") as? [String] ?? []
    let sunClose = hours["Sunday"]?["To"]??.componentsSeparatedByString?(":") as? [String] ?? []

    // ...
}

它相当快，安全，没那么复杂。

为什么 SwiftyJSON 很慢？

在subscript 访问时，SwiftyJSON 会：

检查密钥是String
再次下标self[key:sub]
检查底层对象是NSDictionary
用提供的键为NSDictionary 下标
用结果构造JSON对象
return

也许编译器优化了一些步骤，但“比原生慢”有些不可避免:)

【讨论】：

感谢您非常详尽的回答！并带有基准！因为我是 Swift 的新手（我想很多人都是 :) 很多编码都是第一次尝试和错误，我按照 SwiftyJSON README 文件中的建议进行了 JSON 解析。看看解析方法的不同示例，我并不后悔从我的项目中退出 swifty，“本机”解析的复杂性并不是真正的问题，并且添加了我不认为 swifty 作为选项的性能差异。
我无意冒犯 Swifty 的创建者，我认为它对很多开发人员都有很大的用处。但是谷歌搜索'swift parse json'几乎只给出使用swifty的结果给我的印象是要走的路。但也许它不适合所有人？ :)
@Simpa 在 Swift 世界中，Google 中的很多热门歌曲都不可信。给人的印象是 Objective-C 已经死了，Cocoapods 被接受为标准等等……事实上，我认为很多这些表象都是有问题的。但是，SwiftyJSON 使用起来太慢了吗？这是另一个问题，但如果你最初得到这些结果，你可能不会注意到。
@DanRosenstark 现在使用 Android，情况更糟。 APIs 改变，但搜索引擎结果没有。根据我的口味，一些简单的任务需要反复试验。我确实注意到我的应用程序中是否存在性能错误，因为我总是在发布之前对它们进行分析，以查看是否写得不好：而且很多时候还有改进的余地。