Question

我只是这一切的新手，所以请原谅我的无知！我有一个Table View，每次打开场景时都会调用它的单元格更新方法（按日期排序）。我试图根据对象上次编辑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”。我的问题是-编写此代码的最佳方法是什么，在cell.update调用中调用以下func会占用大量内存？我该如何写得更好？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)
            }
        }
    }

这里是调用它的Table View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

如果代码能正常工作，那就不错了。
在进行任何性能优化之前编写单元测试和性能测试是一个好主意。因此，您将看到所做的更改不会影响结果并改善性能。您还可以使用Xcode工具，通过单击Product-> Profile并选择Time profile and Allocations工具来了解您的代码如何精确地使用CPU和内存。不要忘记性能优化通常是内存和CPU使用率之间的折衷。

您应该将逻辑与表示法分开。这样您就可以编写单元测试。另外，您可以静态保留DateFrommater，而不是每次绘制单元格都将其初始化。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)
        }
    }
}

此类可在您的更新方法中使用，如下所示：

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

或者您可以在ViewController中保留DateMapper并直接在cellForRowAt上使用它。

此类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
    }
}

在控制台上，您将看到将Date转换为String所需的时间：

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

动态更改cell.update Date函数？

1 个答案: