在 SwiftUI 中使用 DatePicker 的 ObservableObject

Question

你能帮我提供以下源代码吗：

import SwiftUI


class DateHandler {
    
    /* create a variable
     Class to manage start date and end date
    */
    

    var date1 : Date {
        didSet{
            print("StartDate: \(date1)")
        }
    }
    var date2 : Date {
        didSet{
            print("EndDate: \(date2)")
        }
    }
    
    var startDate:Date {
        get{
            return date1
        }
        
        set(newValue){
            date1 = toLocalTime(date: newValue)
        }
        
    }
    
    var endDate:Date {
        get{
            return date2
        }
        
        set(newValue){
            date2 = addOneDay(date: toLocalTime(date: newValue))
        }
        
    }
    
    init(){
        self.date1 = Date()
        self.date2 = Date()
    }
    
    
    //Customize time zone
    func toLocalTime(date : Date) -> Date {
    
        
        //Auswahl der aktuellen Kalender
        let calendar = Calendar.current
        
        //Auswahl der Zeitzone
        let timezone = TimeZone.current
        
        //Bestimmen Anzahl Sekunden zwischen Zeitzone und GMT
        let seconds = TimeInterval(timezone.secondsFromGMT(for: date))
        
        //Anpassen des eingelesenen Werts
        let newDate = calendar.date(bySettingHour: 00, minute: 00, second: 00, of: date)
        let dateLocalTimezone = Date(timeInterval: seconds, since: newDate!)

        return dateLocalTimezone
    }
    
    func addOneDay(date : Date) -> Date {

        let tomorrow = Calendar.current.date(byAdding: .day, value: 1, to: date)
        return tomorrow!
    }

}

//Class to use DateHandler() as a ObservableObject
class DateHandlerHelper : ObservableObject{
    
    @Published var dateHandler = DateHandler()
    
}



struct ContentView: View {
    
    @ObservedObject var dateHandlerHelper = DateHandlerHelper()
    
    @State var startDateHelper = Date()
    @State var endDateHelper = Date()
    

    var body: some View {
        
        DatePicker("Date1", selection: $startDateHelper)
            .onAppear(perform: {
                print("onAppear")
                dateHandlerHelper.dateHandler.startDate = startDateHelper
                print(dateHandlerHelper.dateHandler.startDate)
                
            })
            .onChange(of: startDateHelper) { newValue in
                
                print("onChange")
                
                dateHandlerHelper.dateHandler.startDate = newValue
                
                if newValue > endDateHelper{
                    print("Correction Date 1")
                    startDateHelper = endDateHelper
                    dateHandlerHelper.dateHandler.startDate = endDateHelper
                    
                    
                }
                

                print(dateHandlerHelper.dateHandler.startDate)
            }
        
        
        DatePicker("Date2", selection: $endDateHelper)
            .onAppear(perform: {
                
                dateHandlerHelper.dateHandler.endDate = endDateHelper
                print(dateHandlerHelper.dateHandler.endDate)
            })
            .onChange(of: endDateHelper) { newValue in
                print("onChange")
                dateHandlerHelper.dateHandler.endDate = newValue
                print(dateHandlerHelper.dateHandler.endDate)
            }
                
    }
}

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

我有一个带有两个 DatePicker 的视图来选择开始日期和结束日期。对于开始日期和结束日期，有 DateHandler 类。

我想将 DateHandler 类作为 ObservableObject 处理。由于使用了getter/setter函数，我只能通过DateHandlerHelper类间接寻址DateHandler类。这里有更好/更简单的方法吗？

如果我直接通过 DatePickers 处理变量 dateHandlerHelper.dateHandler.startDate 和 dateHandlerHelper.dateHandler.endDate，我可以更改值，但 DatePickers 本身不会更新。为此，我在视图中引入了变量 startDateHelper 和 endDateHelper。你知道我可以如何以不同的方式来保存变量吗？

Answer 1

我不明白为什么每次都需要进行这些日期计算，而是我更改了它们以便在初始化 DateHelper 类时完成一次。

class DateHandler: ObservableObject {
    @Published var startDate: Date
    @Published var endDate: Date

    init(){
        startDate = Self.toLocalTime(date: .now)
        //I assume endDate also should be adjusted for local time?
        let date = Self.addOneDay(date: .now) 
        endDate = Self.toLocalTime(date: date)
    }

    private static func toLocalTime(date : Date) -> Date {
        // removed for brevity
    }

    private static func addOneDay(date : Date) -> Date {
        // removed for brevity
    }
}

然后视图会简单得多

struct ContentView: View {
    @ObservedObject var dateHandler = DateHandler()

    var body: some View {
        VStack {
            DatePicker("Date1", selection: $dateHandler.startDate)
            DatePicker("Date2", selection: $dateHandler.endDate)
        }
    }
}

Answer 2

这似乎是正确的方法：

class DateModel : ObservableObject{

var date1 : Date{
    didSet{
        print(date1)
    }
}
var date2 : Date{
    didSet{
        print(date2)
    }
}

var startDate:Date {
    get{
        return date1
    }
    
    set(newValue){
    
        date1 = toLocalTime(date: newValue)
        startDateString = date1.toString()
        print(startDateString)
            
    }
    
}


var endDate:Date {
    get{
        return date2
    }
    
    set(newValue){
        date2 = toLocalTime(date: newValue)
    }
    
}

init(){
    self.date1 = Date()
    self.date2 = Date()
}



//Customize time zone
func toLocalTime(date : Date) -> Date {

    //Selection of the current calendar
    let calendar = Calendar.current
    
    //Time zone selection
    let timezone = TimeZone.current
    
    //Determine number of seconds between time zone and GMT
    let seconds = TimeInterval(timezone.secondsFromGMT(for: date))
    
    //Adjusting the input value
    let newDate = calendar.date(bySettingHour: 00, minute: 00, second: 00, of: date)
    let dateLocalTimezone = Date(timeInterval: seconds, since: newDate!)

    return dateLocalTimezone
}

}

struct ContentView: View {

@ObservedObject var dateModel = DateModel()

var dateFormatter: DateFormatter {
    let formatter = DateFormatter()
    formatter.dateStyle = .long
    return formatter
}

var body: some View {
    
    Form{
        Section{
            
            DatePicker("start date", selection: $dateModel.startDate, displayedComponents: [.date]).onChange(of: dateModel.startDate) { newValue in
                print(newValue.toString())
            }
            
            DatePicker("final date", selection: $dateModel.endDate, displayedComponents: [.date])
            

            

        }
        
    }
            
}
}