title: flutter - make dynamic mark event in calendar plugin
body: <p>I want to mark the event once every <code>4 days</code>.</p>
  
  <p>example today is the <code>1st</code>, mark the event will be available on the <code>5th</code>, <code>10th</code>, <code>15th</code>, <code>20th</code>, <code>25th</code>, <code>30th</code>, etc.</p>
  
  <p>if today is the <code>3rd</code>, the event will be available on the <code>8th</code>, <code>13th</code>, <code>18th</code>, etc.</p>
  
  <p><strong>how does that function work?</strong></p>
  
  <p>I use this calendar plugin</p>
  
  <p><a href="https://pub.dev/packages/flutter_calendar_carousel" rel="nofollow noreferrer">https://pub.dev/packages/flutter_calendar_carousel</a></p>
  
  <p>Following is the function to mark event manually:</p>
  
  <pre><code>EventList&lt;Event&gt; _markedDateMap = new EventList&lt;Event&gt;();
  
     build(){
         _calendarCarouselNoHeader = CalendarCarousel&lt;Event&gt;(
         ...
         markedDatesMap: _markedDateMap,
         ...
         ),
      }
  
   @override
    void initState() {
  
       _markedDateMap.add(
           new DateTime(2020, 2, 26),
          new Event(
           date: new DateTime(2020, 2, 26),
           title: 'Event 5',
           icon: _eventIcon,
           ));
  
       _markedDateMap.add(
           new DateTime(2020, 2, 26),
          new Event(
           date: new DateTime(2020, 2, 26),
           title: 'Event 5',
           icon: _eventIcon,
           ));
  
      super.initState();
  }
  </code></pre>
  
  <p><strong>Any anwser will appreciated.</strong></p>