动态改变 cell.update 日期函数？

Question

我对这一切都是新手，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）。我正在尝试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 "Yesterday" 等。我的问题是 - 编写此代码的最佳方式是什么，并在我的 cell.update 调用中调用以下函数内存密集型？我怎样才能写得更好？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)
            }
        }
    }

这是从中调用的 Table 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

如果代码有效，那一定不错。
在任何性能优化之前编写单元测试和性能测试是个好主意。所以您会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 Product->Profile 和 select Time profile and Allocations 工具。不要忘记性能优化通常是内存和 CPU 使用之间的权衡。

您应该将逻辑与表示分开。所以你可以编写单元测试。您也可以静态保留 DateFrommater 而不是每次绘制单元格时都初始化它。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 class 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)
   }

或者您可以在 ViewController 处保留 DateMapper 并直接在 cellForRowAt 处使用它。

这个class可以用单元测试覆盖：

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，您将看到将 Date 转换为 String 需要多长时间：

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

动态改变 cell.update 日期函数？

Dynamically changing cell.update Date function?

ios

swift

uitableview

date

nsdate