void XmlSelectCommandExecute()
 {
     string[] files = ExDialogs.SelectionFiles(Properties.Resources.ToolItemButtonChooseXml, new[] { ".xml" });
     foreach (string file in files)
     {
         if (File.Exists(file) && !Xmls.Exists(file))
         {
             Xmls.Add(file);
         }
     }
 }
 void FileDropCommandExecute(object param)
 {
     string[] files = param as string[];
     if (files != null)
     {
         foreach (string file in files)
         {
             if (!File.Exists(file))
             {
                 continue;
             }
             string ext = Path.GetExtension(file).ToLower();
             if (ext == ".sch")
             {
                 Schema = new DocumentSchemaModel(file);
             }
             else if (ext == ".xml" && !Xmls.Exists(file))
             {
                 Xmls.Add(file);
             }
         }
     }
 }