How can I validate multiple properties when any of them changes?

Question

I have two date fields: StartDate and EndDate. StartDate must be earlier than EndDate.

If the user changes the StartDate to something greater than the EndDate, a red

Answer 1

You can also subscribe to the SelectedDateChanged event handler and update needed binding.

BindingExpression expression = datePickerStartDate.GetBindingExpression(DatePicker.SelectedDateProperty);
if (expression != null)
{
    expression.UpdateSource();
}