版本记录

版本号	时间
V1.0	2020.07.04 星期日

前言

前面写了那么多篇主要着眼于局部问题的解决，包括特定功能的实现、通用工具类的封装、视频和语音多媒体的底层和实现以及动画酷炫的实现方式等等。接下来这几篇我们就一起看一下关于iOS系统架构以及独立做一个APP的架构设计的相关问题。感兴趣的可以看上面几篇。
1. 架构之路（一） —— iOS原生系统架构（一）
2. 架构之路（二） —— APP架构分析（一）
3. 架构之路（三） —— APP架构之网络层分析（一）
4. 架构之路（四） —— APP架构之工程实践中网络层的搭建（二）
5. 架构之路（五） —— VIPER架构模式（一）
6. 架构之路（六） —— VIPER架构模式（二）
7. 架构之路（七） —— iOS App的SOLID原则（一）

源码

1. Swift

修改之前

首先看下工程组织结构

下面就是源码了

1. Date.swift

import Foundation

extension Date {
  var startOfDay: Date {
    return Calendar.current.startOfDay(for: self)
  }

  var startOfMonth: Date {
    let calendar = Calendar(identifier: .gregorian)
    let components = calendar.dateComponents([.year, .month], from: self)

    return calendar.date(from: components) ?? Date()
  }

  var startOfWeek: Date {
    let calendar = Calendar(identifier: .gregorian)
    let components = calendar.dateComponents([.yearForWeekOfYear, .weekOfYear], from: self)

    return calendar.date(from: components) ?? Date()
  }

  var endOfDay: Date {
    var components = DateComponents()
    components.day = 1
    components.second = -1
    return Calendar.current.date(byAdding: components, to: startOfDay) ?? Date()
  }

  var endOfMonth: Date {
    var components = DateComponents()
    components.month = 1
    components.second = -1
    return Calendar(identifier: .gregorian).date(byAdding: components, to: startOfMonth) ?? Date()
  }

  var endOfWeek: Date {
    var components = DateComponents()
    components.weekOfYear = 1
    components.second = -1
    return Calendar(identifier: .gregorian).date(byAdding: components, to: startOfWeek) ?? Date()
  }
}

2. ExpenseModel+CoreDataClass.swift

import Foundation
import CoreData

@objc(ExpenseModel)
public class ExpenseModel: NSManagedObject {
}

3. ExpenseModel+CoreDataProperties.swift

import Foundation
import CoreData


extension ExpenseModel {
  @nonobjc
  public class func fetchRequest() -> NSFetchRequest<ExpenseModel> {
    return NSFetchRequest<ExpenseModel>(entityName: "ExpenseModel")
  }

  @NSManaged public var title: String?
  @NSManaged public var price: Double
  @NSManaged public var comment: String?
  @NSManaged public var date: Date?
  @NSManaged public var id: UUID?
}

extension ExpenseModel: Identifiable {
}

4. DailyReportsDataSource.swift

import CoreData
import Combine

class DailyReportsDataSource: ObservableObject {
  var viewContext: NSManagedObjectContext

  @Published private(set) var currentEntries: [ExpenseModel] = []

  init(viewContext: NSManagedObjectContext = AppMain.container.viewContext) {
    self.viewContext = viewContext
    prepare()
  }

  func prepare() {
    currentEntries = getEntries()
  }

  private func getEntries() -> [ExpenseModel] {
    let fetchRequest: NSFetchRequest<ExpenseModel> = ExpenseModel.fetchRequest()
    fetchRequest.sortDescriptors = [NSSortDescriptor(keyPath: \ExpenseModel.date, ascending: false)]
    fetchRequest.predicate = NSPredicate(
      format: "%@ <= date AND date <= %@",
      Date().startOfDay as CVarArg,
      Date().endOfDay as CVarArg)
    do {
      let results = try viewContext.fetch(fetchRequest)
      return results
    } catch let error {
      print(error)
      return []
    }
  }

  func saveEntry(title: String, price: Double, date: Date, comment: String) {
    let newItem = ExpenseModel(context: viewContext)
    newItem.title = title
    newItem.date = date
    newItem.comment = comment
    newItem.price = price
    newItem.id = UUID()

    if let index = currentEntries.firstIndex(where: { $0.date ?? Date() < date }) {
      currentEntries.insert(newItem, at: index)
    } else {
      currentEntries.append(newItem)
    }

    try? viewContext.save()
  }

  func delete(entry: ExpenseModel) {
    viewContext.delete(entry)
    try? viewContext.save()
  }
}

5. MonthlyReportsDataSource.swift

import CoreData
import Combine

class MonthlyReportsDataSource: ObservableObject {
  var viewContext: NSManagedObjectContext

  @Published private(set) var currentEntries: [ExpenseModel] = []

  init(viewContext: NSManagedObjectContext = AppMain.container.viewContext) {
    self.viewContext = viewContext
    prepare()
  }

  func prepare() {
    currentEntries = getEntries()
  }

  private func getEntries() -> [ExpenseModel] {
    let fetchRequest: NSFetchRequest<ExpenseModel> = ExpenseModel.fetchRequest()
    fetchRequest.sortDescriptors = [NSSortDescriptor(keyPath: \ExpenseModel.date, ascending: false)]
    fetchRequest.predicate = NSPredicate(
      format: "%@ <= date AND date <= %@",
      Date().startOfMonth as CVarArg,
      Date().endOfMonth as CVarArg)
    do {
      let results = try viewContext.fetch(fetchRequest)
      return results
    } catch let error {
      print(error)
      return []
    }
  }

  func saveEntry(title: String, price: Double, date: Date, comment: String) {
    let newItem = ExpenseModel(context: viewContext)
    newItem.title = title
    newItem.date = date
    newItem.comment = comment
    newItem.price = price
    newItem.id = UUID()

    if let index = currentEntries.firstIndex(where: { $0.date ?? Date() < date }) {
      currentEntries.insert(newItem, at: index)
    } else {
      currentEntries.append(newItem)
    }

    try? viewContext.save()
  }

  func delete(entry: ExpenseModel) {
    viewContext.delete(entry)
    try? viewContext.save()
  }
}

6. ContentView.swift

import SwiftUI

struct ContentView: View {
  var body: some View {
    NavigationView {
      List {
        NavigationLink(
          "Today",
          destination: dailyReport
            .navigationTitle("Today"))
        NavigationLink(
          "This Month",
          destination: monthlyReport
            .navigationTitle("This Month"))
      }
      .navigationTitle("Reports")
    }
  }

  var dailyReport: DailyExpensesView {
    let dailyDataSource = DailyReportsDataSource()
    return DailyExpensesView(dataSource: dailyDataSource)
  }

  var monthlyReport: MonthlyExpensesView {
    let monthlyDataSource = MonthlyReportsDataSource()
    return MonthlyExpensesView(dataSource: monthlyDataSource)
  }
}

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}

7. DailyExpensesView.swift

import SwiftUI
import Combine

struct DailyExpensesView: View {
  @State private var isAddPresented = false
  @ObservedObject var dataSource: DailyReportsDataSource

  var body: some View {
    VStack {
      List {
        ForEach(dataSource.currentEntries, id: \.id) { item in
          ExpenseItemView(expenseItem: item)
        }
      }
      TotalView(totalExpense: dataSource.currentEntries.reduce(0) { $0 + $1.price })
    }
    .toolbar {
      Button(action: {
        isAddPresented.toggle()
      }, label: {
        Image(systemName: "plus")
      })
    }
    .fullScreenCover(
      isPresented: $isAddPresented) {
      AddExpenseView { title, price, time, comment in
        dataSource.saveEntry(title: title, price: price, date: time, comment: comment)
      }
    }
    .onAppear {
      dataSource.prepare()
    }
  }
}

struct DailyExpensesView_Previews: PreviewProvider {
  static var previews: some View {
    let reportsDataSource = DailyReportsDataSource(viewContext: AppMain.previewContainer.viewContext)
    DailyExpensesView(dataSource: reportsDataSource)
  }
}

8. MonthlyExpensesView.swift

import SwiftUI
import Combine

struct MonthlyExpensesView: View {
  @State private var isAddPresented = false
  @ObservedObject var dataSource: MonthlyReportsDataSource

  var body: some View {
    VStack {
      List {
        ForEach(dataSource.currentEntries, id: \.id) { item in
          ExpenseItemView(expenseItem: item)
        }
      }
      TotalView(totalExpense: dataSource.currentEntries.reduce(0) { $0 + $1.price })
    }
    .toolbar {
      Button(action: {
        isAddPresented.toggle()
      }, label: {
        Image(systemName: "plus")
      })
    }
    .fullScreenCover(
      isPresented: $isAddPresented) {
      AddExpenseView { title, price, time, comment in
        dataSource.saveEntry(title: title, price: price, date: time, comment: comment)
      }
    }
    .onAppear {
      dataSource.prepare()
    }
  }
}

struct MonthlyExpensesView_Previews: PreviewProvider {
  static var previews: some View {
    let reportsDataSource = MonthlyReportsDataSource(viewContext: AppMain.previewContainer.viewContext)
    MonthlyExpensesView(dataSource: reportsDataSource)
  }
}

9. AddExpenseView.swift

import SwiftUI

struct AddExpenseView: View {
  @Environment(\.presentationMode) var presentation
  var saveClosure: (String, Double, Date, String) -> Void

  @State var title: String = ""
  @State var time = Date()
  @State var comment: String = ""
  @State var price: String = ""
  @State var saveDisabled = true
  var body: some View {
    NavigationView {
      VStack(alignment: .leading) {
        Text("Title:")
        TextField("Entry Title", text: $title)
          .onChange(of: title) { _ in
            validateNonEmptyFields()
          }
          .padding(.bottom)
        Text("Amount:")
        TextField("Expense Amount", text: $price)
          .keyboardType(.numberPad)
          .onChange(of: price) { _ in
            validateNonEmptyFields()
          }
          .padding(.bottom)
        DatePicker(
          "Time:",
          selection: $time,
          displayedComponents: [.hourAndMinute])
          .padding(.bottom)
        Text("Comment:")
        TextEditor(text: $comment)
      }
      .padding(.all)
      .navigationBarTitle("Add Expense", displayMode: .inline)
      .navigationBarItems(
        leading: Button(action: cancelEntry) {
          Text("Cancel")
        },
        trailing: Button(action: saveEntry) {
          Text("Save")
        }.disabled(saveDisabled))
    }
  }

  func saveEntry() {
    guard let numericPrice = Double(price), numericPrice > 0 else {
      return
    }

    saveClosure(title, numericPrice, time, comment)
    cancelEntry()
  }

  func cancelEntry() {
    presentation.wrappedValue.dismiss()
  }

  func validateNonEmptyFields() {
    guard Double(price) != nil else {
      saveDisabled = true
      return
    }
    saveDisabled = title.isEmpty
  }
}

struct AddExpenseView_Previews: PreviewProvider {
  static var previews: some View {
    AddExpenseView { _, _, _, _ in
    }
  }
}

10. ExpenseItemView.swift

import SwiftUI

struct ExpenseItemView: View {
  let expenseItem: ExpenseModel

  static let dateFormatter: DateFormatter = {
    var dateFormatter = DateFormatter()
    dateFormatter.dateStyle = .medium
    dateFormatter.timeStyle = .none
    return dateFormatter
  }()

  static let timeFormatter: DateFormatter = {
    var dateFormatter = DateFormatter()
    dateFormatter.dateStyle = .none
    dateFormatter.timeStyle = .medium
    return dateFormatter
  }()

  var body: some View {
    VStack(alignment: .leading) {
      HStack {
        Text(expenseItem.title ?? "")
        Spacer()
        Text(String(format: "%.2f", expenseItem.price))
      }
      Text(expenseItem.comment ?? "")
        .font(.caption)
      HStack {
        Text("\(expenseItem.date ?? Date(), formatter: Self.dateFormatter)")
        Spacer()
        Text("\(expenseItem.date ?? Date(), formatter: Self.timeFormatter)")
      }
    }
  }
}

struct ExpenseItemView_Previews: PreviewProvider {
  static var previews: some View {
    ExpenseItemView(expenseItem: AppMain.previewItem)
  }
}

11. TotalView.swift

import SwiftUI

struct TotalView: View {
  var totalExpense: Double = 0
  var body: some View {
    HStack {
      Text("Total")
      Spacer()
      Text(String(format: "%.2f", totalExpense))
        .font(.title)
    }
    .padding(.horizontal)
  }
}

struct TotalView_Previews: PreviewProvider {
  static var previews: some View {
    TotalView(totalExpense: 123.45)
  }
}

12. AppMain.swift

import SwiftUI
import CoreData

@main
struct AppMain: App {
  static var container: NSPersistentContainer = {
    let container = NSPersistentContainer(name: "ExpensesModel")
    container.loadPersistentStores { _, error in
      if let error = error as NSError? {
        fatalError("Unresolved error \(error), \(error.userInfo)")
      }
    }
    return container
  }()

  static var previewContainer: NSPersistentContainer = {
    let container = NSPersistentContainer(name: "ExpensesModel")
    container.persistentStoreDescriptions.first?.url = URL(fileURLWithPath: "/dev/null")
    container.loadPersistentStores { _, error in
      if let error = error as NSError? {
        fatalError("Unresolved error \(error), \(error.userInfo)")
      }
    }

    for index in 0..<5 {
      let newItem = ExpenseModel(context: container.viewContext)
      newItem.title = "Test Title \(index)"
      newItem.date = Date(timeIntervalSinceNow: Double(index * 60))
      newItem.comment = "Test Comment \(index)"
      newItem.price = Double(index + 1) * 12.3
      newItem.id = UUID()
    }
    do {
      try container.viewContext.save()
    } catch {
      let nsError = error as NSError
      fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
    }

    return container
  }()

  static let previewItem: ExpenseModel = {
    let newItem = ExpenseModel(context: AppMain.previewContainer.viewContext)
    newItem.title = "Preview Item Title"
    newItem.date = Date(timeIntervalSinceNow: 60)
    newItem.comment = "Preview Item Comment"
    newItem.price = 12.34
    newItem.id = UUID()
    return newItem
  }()

  var body: some Scene {
    WindowGroup {
      ContentView()
    }
  }
}

修改之后

首先看下工程组织结构

下面就是源码了

1. ReportReader.swift

import Foundation

class ReportReader: ObservableObject {
  @Published var currentEntries: [ExpenseModelProtocol] = []

  func prepare() {
    assertionFailure("Missing override: Please override this method in the subclass")
  }
}

2. ExpenseModelProtocol.swift

import Foundation

protocol ExpenseModelProtocol {
  var title: String? { get }
  var price: Double { get }
  var comment: String? { get }
  var date: Date? { get }
  var id: UUID? { get }
}

3. SaveEntryProtocol.swift

import Foundation

protocol SaveEntryProtocol {
  func saveEntry(
    title: String,
    price: Double,
    date: Date,
    comment: String
  ) -> Bool
}

4. ReportRange.swift

import Foundation

enum ReportRange: String, CaseIterable {
  case daily = "Today"
  case monthly = "This Month"
  case weekly = "This Week"

  func timeRange() -> (Date, Date) {
    let now = Date()
    switch self {
    case .daily:
      return (now.startOfDay, now.endOfDay)
    case .monthly:
      return (now.startOfMonth, now.endOfMonth)
    case .weekly:
      return (now.startOfWeek, now.endOfWeek)
    }
  }
}

5. Date.swift

import Foundation

extension Date {
  var startOfDay: Date {
    return Calendar.current.startOfDay(for: self)
  }

  var startOfMonth: Date {
    let calendar = Calendar(identifier: .gregorian)
    let components = calendar.dateComponents([.year, .month], from: self)

    return calendar.date(from: components) ?? Date()
  }

  var startOfWeek: Date {
    let calendar = Calendar(identifier: .gregorian)
    let components = calendar.dateComponents([.yearForWeekOfYear, .weekOfYear], from: self)

    return calendar.date(from: components) ?? Date()
  }

  var endOfDay: Date {
    var components = DateComponents()
    components.day = 1
    components.second = -1
    return Calendar.current.date(byAdding: components, to: startOfDay) ?? Date()
  }

  var endOfMonth: Date {
    var components = DateComponents()
    components.month = 1
    components.second = -1
    return Calendar(identifier: .gregorian).date(byAdding: components, to: startOfMonth) ?? Date()
  }

  var endOfWeek: Date {
    var components = DateComponents()
    components.weekOfYear = 1
    components.second = -1
    return Calendar(identifier: .gregorian).date(byAdding: components, to: startOfWeek) ?? Date()
  }
}

6. ExpenseModel+CoreDataClass.swift

import Foundation
import CoreData

@objc(ExpenseModel)
public class ExpenseModel: NSManagedObject {
}

7. ExpenseModel+CoreDataProperties.swift

import Foundation
import CoreData


extension ExpenseModel {
  @nonobjc
  public class func fetchRequest() -> NSFetchRequest<ExpenseModel> {
    return NSFetchRequest<ExpenseModel>(entityName: "ExpenseModel")
  }

  @NSManaged public var title: String?
  @NSManaged public var price: Double
  @NSManaged public var comment: String?
  @NSManaged public var date: Date?
  @NSManaged public var id: UUID?
}

extension ExpenseModel: Identifiable {
}

8. ReportsDataSource.swift

import CoreData
import Combine

class ReportsDataSource: ReportReader, SaveEntryProtocol {
  let reportRange: ReportRange

  init(
    viewContext: NSManagedObjectContext = PersistenceController.shared.container.viewContext,
    reportRange: ReportRange
  ) {
    self.viewContext = viewContext
    self.reportRange = reportRange
    super.init()
    currentEntries = getEntries()
  }

  override func prepare() {
    currentEntries = getEntries()
  }

  var viewContext: NSManagedObjectContext

  private func getEntries() -> [ExpenseModelProtocol] {
    let fetchRequest: NSFetchRequest<ExpenseModel> =
      ExpenseModel.fetchRequest()
    fetchRequest.sortDescriptors = [NSSortDescriptor(keyPath: \ExpenseModel.date, ascending: false)]
    let (startDate, endDate) = reportRange.timeRange()
    fetchRequest.predicate = NSPredicate(
      format: "%@ <= date AND date <= %@",
      startDate as CVarArg,
      endDate as CVarArg)
    do {
      let results = try viewContext.fetch(fetchRequest)
      return results
    } catch let error {
      print(error)
      return []
    }
  }

  func saveEntry(title: String, price: Double, date: Date, comment: String) -> Bool {
    let newItem = ExpenseModel(context: viewContext)
    newItem.title = title
    newItem.date = date
    newItem.comment = comment
    newItem.price = price
    newItem.id = UUID()

    if let index = currentEntries.firstIndex(where: { $0.date ?? Date() < date }) {
      currentEntries.insert(newItem, at: index)
    } else {
      currentEntries.append(newItem)
    }

    try? viewContext.save()
    return true
  }

  func delete(entry: ExpenseModel) {
    viewContext.delete(entry)
    try? viewContext.save()
  }
}

9. Persistence.swift

import Foundation
import CoreData

struct PersistenceController {
  static let shared = PersistenceController()

  let container: NSPersistentContainer

  init(inMemory: Bool = false) {
    container = NSPersistentContainer(name: "ExpensesModel")
    if inMemory {
      container.persistentStoreDescriptions.first?.url = URL(
        fileURLWithPath: "/dev/null")
    }
    container.loadPersistentStores { _, error in
      if let error = error as NSError? {
        fatalError("Unresolved error \(error), \(error.userInfo)")
      }
    }
  }
}

10. ExpenseModel+Protocol.swift

import Foundation

extension ExpenseModel: ExpenseModelProtocol { }

11. ContentView.swift

import SwiftUI

struct ContentView: View {
  var body: some View {
    NavigationView {
      List {
        ForEach(ReportRange.allCases, id: \.self) { value in
          NavigationLink(
            value.rawValue,
            destination: expenseView(for: value)
              .navigationTitle(value.rawValue))
        }
      }
      .navigationTitle("Reports")
    }
  }

  func expenseView(for range: ReportRange) -> ExpensesView {
    let dataSource = ReportsDataSource(reportRange: range)
    return ExpensesView(dataSource: dataSource)
  }
}

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}

12. ExpensesView.swift

import SwiftUI
import Combine

struct ExpensesView: View {
  @State private var isAddPresented = false
  @ObservedObject var dataSource: ReportReader

  var body: some View {
    VStack {
      List {
        ForEach(dataSource.currentEntries, id: \.id) { item in
          ExpenseItemView(expenseItem: item)
        }
      }
      TotalView(totalExpense: dataSource.currentEntries.reduce(0) { $0 + $1.price })
    }
    .toolbar {
      Button(action: {
        isAddPresented.toggle()
      }, label: {
        Image(systemName: "plus")
      })
    }
    .fullScreenCover(isPresented: $isAddPresented) { () -> AddExpenseView? in
      guard let saveHandler = dataSource as? SaveEntryProtocol else {
        return nil
      }
      return AddExpenseView(saveEntryHandler: saveHandler)
    }
    .onAppear {
      dataSource.prepare()
    }
  }
}

struct ExpensesView_Previews: PreviewProvider {
  struct PreviewExpenseEntry: ExpenseModelProtocol {
    var title: String?
    var price: Double
    var comment: String?
    var date: Date?
    var id: UUID? = UUID()
  }

  class PreviewReportsDataSource: ReportReader, SaveEntryProtocol {
    override init() {
      super.init()
      for index in 1..<6 {
        _ = saveEntry(
          title: "Test Title \(index)",
          price: Double(index) * 12.3,
          date: Date(timeIntervalSinceNow: Double(index * -60)),
          comment: "Test Comment \(index)")
      }
    }

    override func prepare() {
    }

    func saveEntry(
      title: String,
      price: Double,
      date: Date,
      comment: String
    ) -> Bool {
      let newEntry = PreviewExpenseEntry(
        title: title,
        price: price,
        comment: comment,
        date: date)
      currentEntries.append(newEntry)
      return true
    }
  }

  static var previews: some View {
    ExpensesView(dataSource: PreviewReportsDataSource())
  }
}

13. AddExpenseView.swift

import SwiftUI

struct AddExpenseView: View {
  @Environment(\.presentationMode) var presentation
  var saveEntryHandler: SaveEntryProtocol

  @State var title: String = ""
  @State var time = Date()
  @State var comment: String = ""
  @State var price: String = ""
  @State var saveDisabled = true

  var body: some View {
    NavigationView {
      VStack(alignment: .leading) {
        Text("Title:")
        TextField("Entry Title", text: $title)
          .onChange(of: title) { _ in
            validateNonEmptyFields()
          }
          .padding(.bottom)
        Text("Amount:")
        TextField("Expense Amount", text: $price)
          .keyboardType(.numberPad)
          .onChange(of: price) { _ in
            validateNonEmptyFields()
          }
          .padding(.bottom)
        DatePicker(
          "Time:",
          selection: $time,
          displayedComponents: [.hourAndMinute])
          .padding(.bottom)
        Text("Comment:")
        TextEditor(text: $comment)
      }
      .padding(.all)
      .navigationBarTitle("Add Expense", displayMode: .inline)
      .navigationBarItems(
        leading: Button(action: cancelEntry) {
          Text("Cancel")
        },
        trailing: Button(action: saveEntry) {
          Text("Save")
        }
        .disabled(saveDisabled))
    }
  }

  func saveEntry() {
    guard let numericPrice = Double(price), numericPrice > 0 else {
      return
    }

    guard saveEntryHandler.saveEntry(
      title: title,
      price: numericPrice,
      date: time,
      comment: comment)
    else {
      print("Invalid entry.")
      return
    }

    cancelEntry()
  }

  func cancelEntry() {
    presentation.wrappedValue.dismiss()
  }

  func validateNonEmptyFields() {
    guard Double(price) != nil else {
      saveDisabled = true
      return
    }
    saveDisabled = title.isEmpty
  }
}

struct AddExpenseView_Previews: PreviewProvider {
  class PreviewSaveHandler: SaveEntryProtocol {
    func saveEntry(title: String, price: Double, date: Date, comment: String) -> Bool {
      return true
    }
  }
  static var previews: some View {
    AddExpenseView(saveEntryHandler: PreviewSaveHandler())
  }
}

14. ExpenseItemView.swift

import SwiftUI

struct ExpenseItemView: View {
  let expenseItem: ExpenseModelProtocol

  static let dateFormatter: DateFormatter = {
    var dateFormatter = DateFormatter()
    dateFormatter.dateStyle = .medium
    dateFormatter.timeStyle = .none
    return dateFormatter
  }()

  static let timeFormatter: DateFormatter = {
    var dateFormatter = DateFormatter()
    dateFormatter.dateStyle = .none
    dateFormatter.timeStyle = .medium
    return dateFormatter
  }()

  var body: some View {
    VStack(alignment: .leading) {
      HStack {
        Text(expenseItem.title ?? "")
        Spacer()
        Text(String(format: "%.2f", expenseItem.price))
      }
      Text(expenseItem.comment ?? "")
        .font(.caption)
      HStack {
        Text("\(expenseItem.date ?? Date(), formatter: Self.dateFormatter)")
        Spacer()
        Text("\(expenseItem.date ?? Date(), formatter: Self.timeFormatter)")
      }
    }
  }
}

struct ExpenseItemView_Previews: PreviewProvider {
  struct PreviewExpenseModel: ExpenseModelProtocol {
    var title: String? = "Preview Item"
    var price: Double = 123.45
    var comment: String? = "This is a preview item"
    var date: Date? = Date()
    var id: UUID? = UUID()
  }

  static var previews: some View {
    ExpenseItemView(expenseItem: PreviewExpenseModel())
  }
}

15. TotalView.swift

import SwiftUI

struct TotalView: View {
  var totalExpense: Double = 0
  var body: some View {
    HStack {
      Text("Total")
      Spacer()
      Text(String(format: "%.2f", totalExpense))
        .font(.title)
    }
    .padding(.horizontal)
  }
}

struct TotalView_Previews: PreviewProvider {
  static var previews: some View {
    TotalView(totalExpense: 123.45)
  }
}

16. AppMain.swift

import SwiftUI
import CoreData

@main
struct AppMain: App {
  static var container: NSPersistentContainer = {
    let container = NSPersistentContainer(name: "ExpensesModel")
    container.loadPersistentStores { _, error in
      if let error = error as NSError? {
        fatalError("Unresolved error \(error), \(error.userInfo)")
      }
    }
    return container
  }()

  static var previewContainer: NSPersistentContainer = {
    let container = NSPersistentContainer(name: "ExpensesModel")
    container.persistentStoreDescriptions.first?.url = URL(fileURLWithPath: "/dev/null")
    container.loadPersistentStores { _, error in
      if let error = error as NSError? {
        fatalError("Unresolved error \(error), \(error.userInfo)")
      }
    }

    for index in 0..<5 {
      let newItem = ExpenseModel(context: container.viewContext)
      newItem.title = "Test Title \(index)"
      newItem.date = Date(timeIntervalSinceNow: Double(index * 60))
      newItem.comment = "Test Comment \(index)"
      newItem.price = Double(index + 1) * 12.3
      newItem.id = UUID()
    }
    do {
      try container.viewContext.save()
    } catch {
      let nsError = error as NSError
      fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
    }

    return container
  }()

  static let previewItem: ExpenseModel = {
    let newItem = ExpenseModel(context: AppMain.previewContainer.viewContext)
    newItem.title = "Preview Item Title"
    newItem.date = Date(timeIntervalSinceNow: 60)
    newItem.comment = "Preview Item Comment"
    newItem.price = 12.34
    newItem.id = UUID()
    return newItem
  }()

  var body: some Scene {
    WindowGroup {
      ContentView()
    }
  }
}

后记

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源码

1. Swift

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架构之路 （八） —— iOS App的SOLID原则（二） 版本记录 前言 源码 后记

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后记

架构之路（八） —— iOS App的SOLID原则（二）版本记录前言源码后记