Joe Stevens' BlogEverything .NET and C#

Download the source code for this post: ReflectionCSV.zip

Last week I wrote a post about generating a CSV from a DataTable. As I hardly use DataTables these days I thought it would be good to write a function that does this for a generic list of objects using reflection to get the properties of the object and export them.

In this example I have done this using an extension method on the generic list. This approach could also be easily applied to the DataTable example.

First I have created a basic object called Person:

public class Person
{
    public string Forename { get; set; }
    public string Surname { get; set; }
    public int Age { get; set; }
}

The next step was to create the extension method on the generic list to generate the CSV data.  It works very much like the method to create the CSV data from the DataTable, but it uses reflection to get the properties for the object type, then iterates through the list to get the values for each property.

using System.Text;
using System.Reflection;

public static class Extensions
{
    public static string GetCSV<T>(this List<T> list)
    {
        StringBuilder sb = new StringBuilder();

        //Get the properties for type T for the headers
        PropertyInfo[] propInfos = typeof(T).GetProperties();
        for (int i = 0; i <= propInfos.Length - 1; i++)
        {
            sb.Append(propInfos[i].Name);

            if (i < propInfos.Length - 1)
            {
                sb.Append(",");
            }
        }

        sb.AppendLine();

        //Loop through the collection, then the properties and add the values
        for (int i = 0; i <= list.Count - 1; i++)
        {
            T item = list[i];
            for (int j = 0; j <= propInfos.Length - 1; j++)
            {
                object o = item.GetType().GetProperty(propInfos[j].Name).GetValue(item, null);
                if (o != null)
                {
                    string value = o.ToString();

                    //Check if the value contans a comma and place it in quotes if so
                    if (value.Contains(","))
                    {
                        value = string.Concat("\"", value, "\"");
                    }

                    //Replace any \r or \n special characters from a new line with a space
                    if (value.Contains("\r"))
                    {
                        value = value.Replace("\r", " ");
                    }
                    if (value.Contains("\n"))
                    {
                        value = value.Replace("\n", " ");
                    }

                    sb.Append(value);
                }

                if (j < propInfos.Length - 1)
                {
                    sb.Append(",");
                }
            }

            sb.AppendLine();
        }

        return sb.ToString();
    }
}

This method can be used to get the CSV string data, and then passed to the following method which I have placed in a static class called CSVHelper:

public static class CSVHelper
{
    public static void ExportCSV(string csv, string filename)
    {
        HttpContext.Current.Response.Clear();
        HttpContext.Current.Response.AddHeader("content-disposition", string.Format("attachment; filename={0}.csv", filename));
        HttpContext.Current.Response.ContentType = "text/csv";
        HttpContext.Current.Response.AddHeader("Pragma", "public");
        HttpContext.Current.Response.Write(csv);
        HttpContext.Current.Response.End();
    }
}

I have added an second extension method which calls GetCSV and ExportCSV so that exporting can be done in a single line, but GetCSV can also be used on it’s own if some other processing is required before exporting:

public static void ExportCSV<T>(this List<T> list, string filename)
{
    string csv = GetCSV(list);
    CSVHelper.ExportCSV(csv, filename);
}

Finally I have created a button on my form to create a new list of Person and export the CSV.  I have also added  a label to display any errors:

protected void btnExport_Click(object sender, EventArgs e)
{
    try
    {
        List<Person> people = GetPeople();
        people.ExportCSV("myCSV");
    }
    catch (System.Threading.ThreadAbortException)
    {
        //Thrown then calling Response.End in CSV Helper
    }
    catch(Exception ex)
    {
        lblMessage.Text = string.Concat("An error occurred: ", ex.Message);
    }
}

private List<Person> GetPeople()
{
    return new List<Person>()
    {
        new Person() {Forename = "Joe", Surname="Stevens", Age=26 },
        new Person() {Forename = "Emily", Surname="Stevens", Age=28 },
        new Person() {Forename = "John", Surname="Glazebrook", Age=34 },
        new Person() {Forename = "Sylvain", Surname="Whissell", Age=37 },
        new Person() {Forename = "Leroy", Surname="Phipps", Age=26 }
    };
}

Now any generic list has the GetCSV and ExportCSV methods that will generate a CSV for the objects in the list.

Download the source code for this post: ReflectionCSV.zip