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The code below works well I am trying to figure how to calculate total number of days once the dates have been selected. Thank you so much.

The problem I'm trying to solve:
Select vacation start date - date selector - this part works well
Select vacation end date - date selector - this part works well
Total days =Calculate End date - Start date - I don't know how to conduct the calculations
Total 10 days

Here is my code

class VacationActivity : AppCompatActivity() 

 private var selectedYear = 0
 private var selectedMonth = 0
 private var selectedDay = 0

 @RequiresApi(Build.VERSION_CODES.O)
 override fun onCreate(savedInstanceState: Bundle?) 
 super.onCreate(savedInstanceState)
 setContentView(R.layout.activity_vacation)


 // get view
 val tvDate = findViewById<TextView>(R.id.from_date_view)
 tvDate.setOnClickListener 

 val currentDate = Calendar.getInstance()
 val year = currentDate.get(Calendar.YEAR)
 val month = currentDate.get(Calendar.MONTH)
 val day = currentDate.get(Calendar.DAY_OF_MONTH)


 if (tvDate.text.isNotEmpty()) 
 this.selectedYear
 this.selectedMonth
 this.selectedDay
 

 var listener = DatePickerDialog.OnDateSetListener view, selectedYear, selectedMonth, selectedDay ->
 this.selectedYear = selectedYear
 this.selectedMonth = selectedMonth
 this.selectedDay = selectedDay

 tvDate.text = "$selectedMonth + 1/$selectedDay/$selectedYear"

 
 val datePicker = DatePickerDialog(this, listener, year, month, day)
 datePicker.show()
 


 val tvDate2 = findViewById<TextView>(R.id.to_date_view)
 tvDate2.setOnClickListener 

 val currentDate = Calendar.getInstance()
 val year = currentDate.get(Calendar.YEAR)
 val month = currentDate.get(Calendar.MONTH)
 val day = currentDate.get(Calendar.DAY_OF_MONTH)


 if (tvDate2.text.isNotEmpty()) 
 this.selectedYear
 this.selectedMonth
 this.selectedDay
 

 var listener = DatePickerDialog.OnDateSetListener view, selectedYear, selectedMonth, selectedDay ->
 this.selectedYear = selectedYear
 this.selectedMonth = selectedMonth
 this.selectedDay = selectedDay

 tvDate2.text = "$selectedMonth + 1/$selectedDay/$selectedYear"
 

 val datePicker = DatePickerDialog(this, listener, year, month, day)
 datePicker.show()


 


 
 

You can use these functions:

fun getLocalDateFromString(d: String, format: String): LocalDate 
 return LocalDate.parse(d, DateTimeFormatter.ofPattern(format))

it returns a LocalDate from a string d formatted with format.

fun getDaysDif(fromDate: LocalDate, toDate: LocalDate): Long 
 return ChronoUnit.DAYS.between(fromDate, toDate)

it returns the difference in days between 2 dates (LocalDate)

So you can do:

val days = getDaysDif(
 getLocalDateFromString(tvDate1.text, "MM/dd/yyyy"),
 getLocalDateFromString(tvDate2.text, "MM/dd/yyyy"))

The above code works for API level 26 and above.

For lower versions, use this:

val format = SimpleDateFormat("MM/dd/yyyy")
val days = TimeUnit.DAYS.convert(
 format.parse(tvDate2.text).getTime() - 
 format.parse(tvDate1.text).getTime(), 
 TimeUnit.MILLISECONDS)