动态改变 cell.update 日期函数？

Question

我对这一切都是新手，所以请原谅我的无知！我有一个Table View，每次打开场景时我都会调用一个单元格更新方法（它按日期排序）。我试图根据上次编辑对象的时间动态显示不同的日期格式。示例：如果日期是今天，则显示时间，如果日期是昨天，则显示“昨天”等。我的问题是 - 编写此代码的最佳方法是什么，并且在我的 cell.update 调用中调用以下函数会占用大量内存？我怎样才能更好地写这个？任何帮助将不胜感激！

func update(with fitnessInfo: Fitness) {
    if let date = fitnessInfo.dateEdited as Date? {
        let today = Calendar.current.isDateInToday(date)
        let yesterdayFunc = Calendar.current.isDateInYesterday(date)
        let yesterday = date.addingTimeInterval(172800)
        let withinSevenDays = date.addingTimeInterval(604800)
        let dateFormatter = DateFormatter()

        func setdate(_ dateFormatter: DateFormatter) {
            let convertedDate = dateFormatter.string(from: date)
            fitnessDateLabel.text = convertedDate
        }
        if today == true {
            dateFormatter.dateFormat = "h:mm a"
            setdate(dateFormatter)
        } else if yesterdayFunc == true {
            fitnessDateLabel.text = "Yesterday"
        } else {
            switch date {
            case yesterday...withinSevenDays:
                dateFormatter.dateFormat = "EEEE"
                setdate(dateFormatter)
            default:
                dateFormatter.dateFormat = "MMMM dd, yyyy"
                setdate(dateFormatter)
            }
        }
    }

这是调用它的表视图函数 (cellForRowAt)。

tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: “fitnessCell", for: indexPath) as! FitnessTableViewCell
        let fitnessInfo = fetchedRC.object(at: indexPath)
        cell.update(with: fitnessInfo)
        return cell
    }

Answer 1

1. 如果代码可以正常工作，那也不错。
2. 最好在进行任何性能优化之前编写单元测试和性能测试。因此，您将看到您的更改不会影响结果并提高性能。您还可以使用 Xcode 工具来了解您的代码究竟如何使用 CPU 和内存，方法是单击产品->配置文件并选择时间配置文件和分配工具。不要忘记，性能优化通常是内存和 CPU 使用率之间的权衡。

3. 您应该将逻辑与演示分开。所以你可以编写单元测试。您也可以静态保留 DateFrommater，而不是在每次绘制单元格时对其进行初始化。这是一个如何完成的示例：

   final class DateMapper {
       static let todayDateFormatter = DateFormatter()
       static let lastWeekAgoDateFormatter = DateFormatter()
       static let moreThanWeekAgoDateFormatter = DateFormatter()
       let today: Date
       let currentCalendar = Calendar.current
   
       init(today: Date) {
           self.today = today
           DateMapper.todayDateFormatter.dateFormat = "h:mm a"
           DateMapper.lastWeekAgoDateFormatter.dateFormat = "EEEE"
           DateMapper.moreThanWeekAgoDateFormatter.dateFormat = "MMMM dd, yyyy"
       }
   
       func formattedDate(date: Date) -> String {
           guard let totalDays = currentCalendar.dateComponents([.day], from: date, to: today).day else {
               return ""
           }
           switch totalDays {
           case 0:
               return DateMapper.todayDateFormatter.string(from: date)
           case 1:
               return "Yesterday"
           case 2...7:
               return DateMapper.lastWeekAgoDateFormatter.string(from: date)
           default:
               return DateMapper.moreThanWeekAgoDateFormatter.string(from: date)
           }
       }
   }
   

这个类可以像这样在你的更新方法中使用：

  func update(with fitnessInfo: Fitness) {
       let dateMapper = DateMapper(today: Date())
       fitnessDateLabel.text = dateMapper.formattedDate(date: fitnessInfo.dateEdited)
   }

或者你可以在 ViewController 中保留 DateMapper 并在 cellForRowAt 中直接使用它。

4. 这个类可以被单元测试覆盖：

   class ExampleTests: XCTestCase {
   
       var dateMapper: DateMapper {
           let todayStub = dateStubByComponents(year: 2019, month: 5, day: 4, hour: 12)
           return DateMapper(today: todayStub)
       }
   
       func testTodayDate() {
           // arrange
           let todayStub = dateStubByComponents(year: 2019, month: 5, day: 4, hour: 11)
   
           // act
           let result = dateMapper.formattedDate(date: todayStub)
   
           // assert
           XCTAssertEqual(result, "11:00 AM")
       }
   
       func testYestadayDate() {
           // arrange
           let yesterdayStub = dateStubByComponents(year: 2019, month: 5, day: 3, hour: 0)
   
           // act
           let result = dateMapper.formattedDate(date: yesterdayStub)
   
           // assert
           XCTAssertEqual(result, "Yesterday")
       }
   
       func testLastWeekDate() {
           // arrange
           let lastWeekStub = dateStubByComponents(year: 2019, month: 5, day: 2, hour: 0)
   
           // act
           let result = dateMapper.formattedDate(date: lastWeekStub)
   
           // assert
           XCTAssertEqual(result, "Thursday")
       }
   
       func testPerformanceExample() {
           let lastWeekStub = dateStubByComponents(year: 2019, month: 5, day: 2, hour: 0)
           self.measure {
                _ = dateMapper.formattedDate(date: lastWeekStub)
           }
       }
   
       // MARK: Private
   
       private func dateStubByComponents(year: Int, month: Int, day: Int, hour: Int) -> Date {
       var dateStubComponents = DateComponents()
       dateStubComponents.year = year
       dateStubComponents.month = month
       dateStubComponents.day = day
       dateStubComponents.hour = hour
   
       guard let dateStub = Calendar.current.date(from: dateStubComponents) else { fatalError("Date must be valid") }
          return dateStub
       }
   }
   

在控制台中，您将看到将 Date 转换为 String 需要多长时间：

值：[0.000922, 0.000063, 0.000041, 0.000038, 0.000036, 0.000035, 0.000035, 0.000036, 0.000043, 0.000027]