Custom Birthdate Picker Implementation

Question

NeroTgi OP

Created Jan ’23

Replies 1

Boosts 0

Participants 2

Hello!

I am trying to make my own birthdate picker implementation where I want three wheels side-by-side in an HStack. Of course, the values inside these wheels depend on each other, for example, depending on the year, February different number of days, and depending on the month, there are different number of days. I tried making a model for this, but it's returning me the "The compiler is unable to type-check this expression in reasonable time; try breaking up the expression into distinct sub-expressions" error in the init() line. Could you please tell me what's wrong with this?

The picker view:

Section {
              HStack {
                Picker("Year", selection: birthdateModel.$selectedYear) {
                  ForEach(birthdateModel.years, id: \.self) {
                    Text(String($0))
                  }
                }
                .pickerStyle(.wheel)
                Picker("Month", selection: birthdateModel.$selectedMonth) {
                  ForEach(birthdateModel.months, id: \.self) {
                    Text(String($0))
                  }
                }
                .pickerStyle(.wheel)
                Picker("Day", selection: birthdateModel.$selectedDay) {
                  ForEach(birthdateModel.days, id: \.self) {
                    Text(String($0))
                  }
                }
                .pickerStyle(.wheel)
              }
            }

Birthdate model:

class BirthdateModel: Equatable, Hashable {
   
  let monthWith30Days = ["Apr", "Jun", "Sep", "Nov"]
  let monthWith31Days = ["Jan", "Mar", "May", "Jul", "Aug", "Oct", "Dec"]
  var daysInFeb = 28
  let years = 1900...Calendar.current.component(.year, from: Date())
  let months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
  var days = 1...31
  var date = 0
   
  let currentDate = Date()
  let dateFormatter = DateFormatter()
  let monthString = ""
   
  @State var selectedYear: Int = 1900 {
    didSet(year) {
      if ((year % 4 == 0) && (year / 4 != 0)) {
        daysInFeb = 29
      }
      self.changeDate()
    }
  }
  @State var selectedMonth: String = "Jan" {
    didSet(month) {
      if monthWith31Days.contains(month) {
        days = 1...31
      }
      else if monthWith30Days.contains(month) {
        days = 1...30
      }
      else {
        days = 1...daysInFeb
      }
      self.changeDate()
    }
  }
  @State var selectedDay: Int = 1 {
    didSet(day) {
      self.changeDate()
    }
  }
   
  init() {
    self.dateFormatter.dateFormat = "Lll";
    self.monthString = self.dateFormatter.string(from: self.currentDate);
     
    self.selectedYear = Calendar.current.component(.year, from: Date())
    self.selectedMonth = self.monthString
    self.selectedDay = Calendar.current.component(.day, from: Date())
    changeDate()
  }
   
  func hash(into hasher: inout Hasher) {
    hasher.combine(date)
  }
   
  static func ==(lhs: BirthdateModel, rhs: BirthdateModel) -> Bool {
    return lhs.date == rhs.date
  }
   
  func changeDate() {
    self.date = (self.selectedYear * 10000) + ((self.months.firstIndex(where: {$0 == self.selectedMonth}) + 1) * 100) + self.selectedDay
  }
   
}

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Answer 1

Claude31 OP

Jan ’23

Could you please tell me what's wrong with this?

A lot of things.

I suppose the error is in changeDate func?

Is it SwiftUI code ? It does not seem.

You use @State in a class which is not valid.
you have an error in test for leap year.

var selectedYear: Int = 1900 { // @State cannot work here
    didSet(year) {
        if (year % 4 == 0) && ((year % 100 != 0) || (year / 100) % 4 == 0) {  // <<-- ERROR HERE
            daysInFeb = 29
        }
        self.changeDate()
    }
}

monthString should be a var, not a constant (let)
What is this dateFormat Lll ???
You expect monthString to return "Jan", "Feb",

    self.monthString = self.dateFormatter.string(from: self.currentDate);

but this returns the month number (01, 02, …). Hence

self.months.firstIndex(where: {$0 == self.selectedMonth})

is nil !

So you must use the proper format:

    self.dateFormatter.dateFormat = "MMM" // "Lll";

Problem is also that firstIndex returns optional: compiler cannot add 1 to it.
You have to change as follows (I added some print so that you can understand what happens)

  func changeDate() {
      print(self.selectedMonth, self.months)
      var month = self.months.firstIndex(where: {$0 == self.selectedMonth})
      print(month)
      if let month = month  {
          print(month)
          self.date = (self.selectedYear * 10000) + ((month+1) * 100) + self.selectedDay
      }
  }

Note: are you clear on what you intend to do with date as it is computed (seems to be multiplexing date components).

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