Get the first day of a month in swift - swift

Question

I'm looking for a way to get the first day of a month (in Swift).
I would like to know if it is a Monday, Tuesday etc... by returning the number corresponding.
I try many solution like getting a NSCalendar component .weekDay but no one work.
Example :
print(getTheFirstDate("2016-2-18"))
// Should return : 0 (because the first day of February 2016 is Monday).
Any help would be appreciate.

Answer 1

First you need to parse your date string, then you can use Calendar method dateComponents to get the calendar, year and month components from that date and create a new date from those components. Then you can extract the weekday date component from it:
Xcode 11.5 • Swift 5.2
extension Date {
var weekday: Int { Calendar.current.component(.weekday, from: self) }
var firstDayOfTheMonth: Date {
Calendar.current.dateComponents([.calendar, .year,.month], from: self).date!
}
}
extension String {
static var dateFormatter: DateFormatter = {
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd"
return formatter
}()
var date: Date? {
String.dateFormatter.date(from: self)
}
}
"2016-2-18".date?.firstDayOfTheMonth.weekday // 2 = Monday (Sunday-Saturday 1-7)

Answer 2

extension Date {
var startOfWeek: Date {
let gregorian = Calendar(identifier: .gregorian)
let sunday = gregorian.date(from: gregorian.dateComponents([.yearForWeekOfYear, .weekOfYear], from: self))
return gregorian.date(byAdding: .day, value: 1, to: sunday!)!
}
var endOfWeek: Date {
let gregorian = Calendar(identifier: .gregorian)
let sunday = gregorian.date(from: gregorian.dateComponents([.yearForWeekOfYear, .weekOfYear], from: self))
return gregorian.date(byAdding: .day, value: 7, to: sunday!)!
}
var startOfPreviousWeek: Date {
let gregorian = Calendar(identifier: .gregorian)
let sunday = gregorian.date(from: gregorian.dateComponents([.yearForWeekOfYear, .weekOfYear], from: self))
return gregorian.date(byAdding: .day, value: -6, to: sunday!)!
}
var endOfPreviousWeek: Date {
let gregorian = Calendar(identifier: .gregorian)
let sunday = gregorian.date(from: gregorian.dateComponents([.yearForWeekOfYear, .weekOfYear], from: self))
return gregorian.date(byAdding: .day, value: 0, to: sunday!)!
}
var startDateOfMonth: Date {
return Calendar.current.date(from: Calendar.current.dateComponents([.year, .month], from: Calendar.current.startOfDay(for: self)))!
}
var endDateOfMonth: Date {
return Calendar.current.date(byAdding: DateComponents(month: 1, day: -1), to: self.startDateOfMonth)!
}
var getPreviousMonthDate: Date {
return Calendar.current.date(byAdding: .month, value: -1, to: self)!
}
var startDateOfPreviousMonth: Date {
return getPreviousMonthDate.startDateOfMonth
}
var endOfPreviousMonth: Date {
return getPreviousMonthDate.endDateOfMonth
}
}

Answer 3

Well to get the corresponding number of the day of the week you can use:
var weekday = calendar!.component(NSCalendarUnit.Weekday, fromDate: yourNSDate)
var weekdayName = self.getDayOfWeek(weekday)
Then you can call this function I created to get the corresponding name of the day of the week based on the number passed in to getDayOfWeek()
func getDayOfWeek(weekday:Int) -> String {
if(weekday == 1) {
return "Sunday"
}
else if(weekday == 2) {
return "Monday"
}
else if(weekday == 3) {
return "Tuesday"
}
else if(weekday == 4) {
return "Wednesday"
}
else if(weekday == 5) {
return "Thursday"
}
else if(weekday == 6) {
return "Friday"
}
else {
return "Saturday"
}
}
And if you are using a String as a date to begin with you can change it into an NSDate like this:
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = /*place date format here*/
let date = dateFormatter.dateFromString(/*your_date_string*/)

Answer 4

I like Leo's answer, but in case you want to encapsulate the logic into a single function or don't want to use extensions.
func getDayOfWeekForFirstDayOfMonthFromDateString(dateString:String) -> String? {
let formatter = NSDateFormatter()
formatter.dateFormat = "yyyy-MM-dd"
if let date = formatter.dateFromString(dateString) {
if let firstOfMonth = NSCalendar.currentCalendar().dateFromComponents(NSCalendar.currentCalendar().components([.Year, .Month], fromDate: date)) {
formatter.dateFormat = "EEEE"
return formatter.stringFromDate(firstOfMonth)
}
}
return nil
}
EDIT: Adjusted code to utilize Leo's great suggestion, and borrowed his more terse creation of the creation of the first of the month object. Thanks, Leo!