一场陟遐自迩的 SwiftUI + CoreData 性能优化之旅（上）

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概述

自从 SwiftUI 诞生那天起，我们秃头码农们就仿佛打开了一个全新的撸码世界，再辅以 CoreData 框架的鼎力相助，打造一款持久存储支持的 App 就像探囊取物般的 Easy。

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话虽如此，不过 CoreData 虽好，稍不留神也可能会让代码执行速度“蜗行牛步”，这该如何解决呢？

在本篇博文中，您将学到如下内容：

概述
1. 当前源代码执行的“小瓶颈”
总结

这是两篇偏向撸码的博文，里面有较多的源代码展示，我们会循序渐进地完成整个优化目标，希望大家能够喜欢。

那还等什么呢？让我们马上开始 CoreData 优化大冒险吧！
Let’s go！！！😉

1. 当前源代码执行的“小瓶颈”

要想小试拳脚，我们必须先有需要优化的代码。下面我就满足大家吧：

struct MonthCountsView: View {@Environment(\.managedObjectContext) var contextlet counter: ProjectCounterlet year: Intlet month: Int@State private var isShowMonthCountsChart = falsevar body: some View {// #1let daysCounts = try! counter.queryDaysCounts(year: year, month: month, context: context)// #2let days = daysCounts.keys.sorted(using: SortDescriptor(\.self, order: .reverse))VStack {Button(isShowMonthCountsChart ? "月计数" : "月计数图表") {withAnimation(.bouncy) {isShowMonthCountsChart.toggle()}}.frame(maxWidth: .infinity, alignment: .leading)if isShowMonthCountsChart {MonthCountsChart(counter: counter, daysCountsDict: daysCounts).frame(minHeight: 200)} else {LazyVGrid(columns: [GridItem](repeating: .init(.adaptive(minimum: 100, maximum: 120), spacing: 8), count: 4)) {ForEach(days, id: \.self) { day inlet dayCounts = daysCounts[day]!let totalCount = dayCounts.totalCountNavigationLink {List {LabeledContent("当日总计数") {Text("\(totalCount)\(counter.unit ?? "")").font(.title2).foregroundStyle(counter.nature.data.color)}Section("单次计数") {if let counts = dayCounts.counts {ForEach(counts, id: \.time) { trace inHStack {Text(Common.timeHHmmFt.string(from: trace.time)).monospacedDigit()Spacer()Text("\(trace.count)\(counter.unit ?? "")").font(.title3).foregroundStyle(counter.nature.data.color)}}}}}.listStyle(.plain).navigationTitle(Common.onlyDateFt.string(from: dayCounts.date))} label: {VStack {HStack {Text("\(Common.tinyDateFt.string(from: dayCounts.date))日").font(.headline).frame(maxWidth: .infinity, alignment: .leading)}.padding(.leading).frame(minHeight: 50)Text("\(totalCount)\(Text("\(counter.unit ?? "")").font(.subheadline))").font(.title).padding(.bottom)}.foregroundStyle(.white).monospacedDigit().background(counter.nature.data.color.gradient.opacity(0.88), in: RoundedRectangle(cornerRadius: 10))}}}}}}
}

上面的代码虽然有点冗长，但本质上却很简单。我们主要做了以下几件事：

使用 isShowMonthCountsChart 状态切换月计数图表和 Grid 显示；
在 #1 代码处，我们调用计数器的 queryDaysCounts 方法，来获取指定月的计数记录，返回的结果是一个 [Int: DayCountsData] 字典；
在 #2 代码处，我们将上述字典所有键反向排序并生成所有日的数组，这会将最近的日排在最前面；

为了进一步便于还未秃小码农们的理解，我们下面将缺失的、与计数相关的数据结构一并贴出来：

struct YearCountsData: Identifiable {var id: String {"\(year)"}let year: Intvar totalCount: Int = 0var monthlyAvg: Float = 0.0var monthsCounts: [Int: MonthCountsData]?var monthsCountSortedAry: [MonthCountsData]? {if let data = monthsCounts {let sortedKeys = data.keys.sorted(using: SortDescriptor(\.self, order: .reverse))return sortedKeys.map { data[$0]! }}return nil}}struct MonthCountsData: Identifiable {var id: String {"\(year).\(month)"}let year: Intlet month: Intvar totalCount: Int = 0var daylyAvg: Float = 0.0var daysCounts: [Int: DayCountsData]?var daysCountSortedAry: [DayCountsData]? {if let data = daysCounts {let sortedKeys = data.keys.sorted(using: SortDescriptor(\.self, order: .reverse))return sortedKeys.map { data[$0]! }}return nil}}struct DayCountsData: Identifiable {var id: Date {date}let date: Datevar totalCount: Int = 0var counts: [(time: Date, count: Int)]?}