Quizzy example in code: Duplicate StartDate = startDate

[Youngjae]

Hello.

In WPF RadTimeline First Look example (presidents list)
UpdateCurrentPage() method in ExampleViewModel.cs file has duplicate variable settings as below.

Is there any reason?

this.StartDate = startDate;
this.EndDate = endDate;
this.StartDate = startDate;

this.VisibleStartDate = startDate;
this.VisibleEndDate = endDate;
this.VisibleStartDate = startDate;

[Petar Kirov]

Hello Youngjae,

These duplicate settings of the properties are required because the RadTimeline (and RadTimeBar) internally coerces the PeriodStart/End, VisiblePeriodStart/End and SelectionStart/End properties. For example if PeriodStart is set to a date after PeriodEnd by the user, then the PeriodStart is set to PeriodEnd internally afterwards.

There is a required precedence of the Timeline's (and TimeBar's) properties. This means that the Start Time should always be set before the End Time. The optimal way to set them is in the following order: 

1. PeriodStart
2. PeriodEnd
3. VisiblePeriodStart
4. VisiblePeriodEnd
5. SelectionStart
6. SelectionEnd

In order to make more clear the code from the example I've rewritten in code snippet below: 

//PeriodStart and PeriodEnd
if (this.EndDate < startDate)
{
    this.EndDate = endDate;
    this.StartDate = startDate;
}
else
{
    this.StartDate = startDate;
    this.EndDate = endDate;
}

//VisiblePeriodStart and VisiblePeriodEnd
if (this.VisibleEndDate < newStartDate)
{
    this.VisibleEndDate = endDate;
    this.VisibleStartDate = startDate;
}
else
{
    this.VisibleStartDate = startDate;
    this.VisibleEndDate = endDate;
}

 
All the best,
Petar Kirov
the Telerik team