public string OfflineMapsLocation {get; set;}

//OfflineMaps settings control where map content that is taken
//offline is copied to on the local machine. Options are mutually exclusive.

//Set ApplicationOptions.DownloadOptions.OfflineMapsLocation explicitly to
//toggle ApplicationOptions.DownloadOptions.AskForOfflineMapsLocation and
//ApplicationOptions.DownloadOptions.OfflineMapsToProjectLocation to false
//Note: default is typically <My Documents>\ArcGIS\OfflineMaps, _not_ null.
//This is the same behavior as on the Pro UI.
ApplicationOptions.DownloadOptions.OfflineMapsLocation = @"D:\data\for_offline";

//or...to use a location already stored in OfflineMapsLocation as the
//default without changing it, 
//set ApplicationOptions.DownloadOptions.AskForOfflineMapsLocation and
//ApplicationOptions.DownloadOptions.OfflineMapsToProjectLocation to false
//explicitly.
if (!string.IsNullOrEmpty(ApplicationOptions.DownloadOptions.OfflineMapsLocation))
{
  ApplicationOptions.DownloadOptions.AskForOfflineMapsLocation = false;
  ApplicationOptions.DownloadOptions.OfflineMapsToProjectLocation = false;
}

//Setting ApplicationOptions.DownloadOptions.AskForOfflineMapsLocation to
//true overrides any OfflineMapsLocation value and sets 
//ApplicationOptions.DownloadOptions.OfflineMapsToProjectLocation to false.
//This is the same behavior as on the Pro UI.
ApplicationOptions.DownloadOptions.AskForOfflineMapsLocation = true;

//Setting ApplicationOptions.DownloadOptions.OfflineMapsToProjectLocation to
//true overrides any OfflineMapsLocation value and sets 
//ApplicationOptions.DownloadOptions.AskForOfflineMapsLocation to false.
//This is the same behavior as on the Pro UI.
ApplicationOptions.DownloadOptions.OfflineMapsToProjectLocation = true;