1. Extract method:

   private static string GetExportFilePath(string csvFilePath, DateTime date, string fileSuffix) { return string.Format("{0}{1:yyyy-MM-dd}-{2}.csv", csvFilePath, date, fileSuffix); }

2. Also I would add those selectedExportPath and csvFilePath as parameters to Export method. I hope they are not used anywhere. It is usually pretty subjective whether to add something as method parameters or leave it as class member, but here I would definitely add them as parameters because I also tend to move such methods out from the views and I assume this class is View since you have button click event handlers.

1. You can use an Extract Method refactoring to get rid of the duplicate code:

   private static string GetExportFilePath(string csvFilePath, DateTime date, string fileSuffix)
   {
       return string.Format("{0}{1:yyyy-MM-dd}-{2}.csv", csvFilePath, date, fileSuffix);
   }
   

2. I would add those selectedExportType and path variables as parameters to the Export() method. I hope they are not used anywhere. It is usually pretty subjective whether to add something as method parameters or leave it as class member, but here I would definitely pass them as parameters. I assume this class is a “View” since you have button click event handlers, and I also tend to move such methods out from the views.

If we use these two ideas, your event handlers would be simplified to:

private void btnBuildingList_Click(object sender, EventArgs e)
{
    var path = GetExportFilePath(csvFilePath, datDate.DateTime, "BuildingList.csv");
    Export((int)ExportType.Building, path);
}

private void btnOwnerList_Click(object sender, EventArgs e)
{
    var path = GetExportFilePath(csvFilePath, datDate.DateTime, "OwnerList.csv");
    Export((int)ExportType.Persons, path);
}

private void btnFacts_Click(object sender, EventArgs e)
{
    var path = GetExportFilePath(csvFilePath, datDate.DateTime, "FactsData.csv");
    Export((int)ExportType.Facts, path);
}

1. Extract method:

   private static string GetExportFilePath(string csvFilePath, DateTime date, string fileSuffix) { return string.Format("{0}{1:yyyy-MM-dd}-{2}.csv", csvFilePath, datDate.DateTime, fileSuffix); }

2. Also I would add those selectedExportPath and csvFilePath as parameters to Export method. I hope they are not used anywhere. It is usually pretty subjective whether to add something as method parameters or leave it as class member, but here I would definitely add them as parameters because I also tend to move such methods out from the views and I assume this class is View since you have button click event handlers.

1. Extract method:

   private static string GetExportFilePath(string csvFilePath, DateTime date, string fileSuffix) { return string.Format("{0}{1:yyyy-MM-dd}-{2}.csv", csvFilePath, date, fileSuffix); }

2. Also I would add those selectedExportPath and csvFilePath as parameters to Export method. I hope they are not used anywhere. It is usually pretty subjective whether to add something as method parameters or leave it as class member, but here I would definitely add them as parameters because I also tend to move such methods out from the views and I assume this class is View since you have button click event handlers.