Something like this should do it:

                foreach (Track myTrack in ScriptPortal.Vegas.Tracks)
                {
                    if (myTrack.Selected)
                    {
                        bool selectThisOne = false;
                        foreach(TrackEvent myEvent in myTrack.Events)
                        {
                            myEvent.Selected = selectThisOne;
                            selectThisOne = !selectThisOne;
                        }
                    }
                }

 

Thanks! After tweaking a little bit, I achieved what I want. (I changed the code to allow you to select a file in the multiple of n.) But it selects like first picture(red squares mean selected files) when the file is located in the middle of the track bar, not like the second picture(what I intended) Do you know what is the problem of my code?

Here is my code. (in this case, the number of nthObject is key number)

using System;
using ScriptPortal.Vegas;
public class EntryPoint
{  
    public void FromVegas(Vegas myVegas)
    {
        foreach (Track myTrack in myVegas.Project.Tracks)
        {
            if (myTrack.Selected)
            {
                int objectNum = 0;
                int nthObject = 2; //If you want to change the Nth object to select, change this number to N which you want.
                foreach(TrackEvent myEvent in myTrack.Events)
                {
                    if (myEvent.Start >= myVegas.SelectionStart && myEvent.Start <= (myVegas.SelectionStart + myVegas.SelectionLength))
                    {
                        if (objectNum % nthObject == 0)
                        {
                        myEvent.Selected = true;
                        objectNum++;
                        }
                        else
                        {
                        myEvent.Selected = false;
                        objectNum++;
                        }
                    }
                }
            }
        }
    }
}