C# Excel - Manage column properties.

Question

Scenario is to generate an excel report that has ~ 150 data columns. Now I need to manage the column properties like Width, BackgroundColor, Font etc.

The approach that I am using relies on reflection. I have a class that has ~ 150 constants for column header text. Another custom attribute class to store column properties. These attributes are applied to the constants.

During column creation using reflection I am accessing all the constants to create the header text(Constant ordering in class defines column ordering) and the attribute for column properties.

private void CreateHeader(Excel.Worksheet xl_WorkSheet, FieldInfo[] fi_Header)
    {
        ColumnProperties c;
        System.Attribute[] customAttributes;
        for (int i = 0; i < fi_Header.GetLength(0); i++)
        {
            xl_WorkSheet.get_Range(xl_WorkSheet.Cells[1, i+1], xl_WorkSheet.Cells[2, i+1]).Merge(false);

            //Set the header text.
            xl_WorkSheet.get_Range(xl_WorkSheet.Cells[1, i + 1], xl_WorkSheet.Cells[2, i + 1]).FormulaR1C1 = 
                fi_Header[i].GetValue(null).ToString();
            //Set cell border.
            xl_WorkSheet.get_Range(xl_WorkSheet.Cells[1, i + 1],
                xl_WorkSheet.Cells[2, i + 1]).BorderAround(Excel.XlLineStyle.xlContinuous,
                Excel.XlBorderWeight.xlThin, Excel.XlColorIndex.xlColorIndexAutomatic, Missing.Value);

            //Get custom attribute ~ Column attribute.
            customAttributes = (System.Attribute[])fi_Header[i].GetCustomAttributes(typeof(ColumnProperties), false);
            if (customAttributes.Length > 0)
            {
                c = (ColumnProperties)customAttributes[0];
                //Set column properties.
                xl_WorkSheet.get_Range(xl_WorkSheet.Cells[1, i + 1],
                    xl_WorkSheet.Cells[2, i + 1]).Interior.Color =
                    System.Drawing.ColorTranslator.ToOle(System.Drawing.Color.FromName(c.Color));

                xl_WorkSheet.get_Range(xl_WorkSheet.Cells[1, i + 1],
                    xl_WorkSheet.Cells[2, i + 1]).ColumnWidth = c.Width;
            }                
        }
    }

EDIT: Code to get constants

private FieldInfo[] GetHeaderConstants(System.Type type)
    {
        ArrayList constants = new ArrayList();
        FieldInfo[] fieldInfos = type.GetFields(BindingFlags.Public | BindingFlags.Static | BindingFlags.FlattenHierarchy);
        foreach (FieldInfo fi in fieldInfos)
        {
            if (fi.IsLiteral && !fi.IsInitOnly)
                constants.Add(fi);
        }
        return (FieldInfo[])constants.ToArray(typeof(FieldInfo));
    }   

Main objective is to make the excel file generation generic/less maintainable. Is the approach fine or there are any other better alternatives.

EDIT 2: Constants class

public class ExcelHeaders
{
    [ColumnProperties(Width=10, Color="LemonChiffon")]
    public const string S_NO = "S.No";

    [ColumnProperties(Width = 20, Color = "WhiteSmoke")]
    public const string COLUMN_HEADER = "Header Text";
}

Answer 1

1. Where does the need for reflection come into play?
2. I don't think you can rely on reflection to return your constants in the order in which you declared them in your source code.

Edit:

Well, I must be missing something -- I really don't get what you're reflecting on, if not something of your own creating, and of which you can readily be passed a reference.

It seems like you can create a class like so:

public class ColumnProperties
{
   readonly string m_HeaderText;
   public ColumnProperties(string headerText, Color color, int width) { ... }
   public string HeaderText { get { return m_HeaderText; }
   public Color FontColor { get; set; }
   public int Width { get; set; }
   ...
}

Then if you have 150 datapoints, create 150 ColumnProperties objects. Pass a collection of these into your CreateHeader() method, and forget about all that gratuitous reflection and those custom attributes.

Answer 2

One characteristic of your approach is that you will need to change your source if you want to change a column's appearance. I would prefer storing the appearance data in some kind of XML configuration. You could load the configuration from an external configuration file if available, else from a default configuration that's embedded in the executable as a resource. This gives you the flexibility to change the configuration at runtime simply by adding a configuration file.

Your XML document might look like:

  <Appearance>
    <!-- Defaults to use for attributes not explicitly specified -->
    <Defaults HeaderText="" Width="10" Color="White" />
    <Columns>
      <Column HeaderText="S.No" Width="10" Color="LemonChiffon" />
      <Column HeaderText="Header Text" Width="20" Color="WhiteSmoke" />
    </Columns>
  </Appearance>