here is how you can do it
Converting your String into Array of String
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string str = "aa,dd,ff,ggg,yy";
/* Convert to Array */
string[] StringArr = str.Split(',');
Converting your String into List<T> object
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/* Convert to List<t> */
string str = "aa,dd,ff,ggg,yy";
List<string> ListObject = str.Split(',').ToList<string>();