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

本篇主要讲述了iOS App的SOLID原则，感兴趣的给个赞或者关注~~~