I have a custom field that inherits the Number field (I change the UI of the field, but not the storage).

When I export to Excel a list that contains an instance of this field, I get different behaviors:

  • With Excel 2013, the field is available
  • With Excel 2003, the field is not available

Is there any restriction with Excel 2003 and custom fields?

Is there a workaround?

I've tried to create a calculated column that just replicate the value of the column (with a number output). The column shows the correct value in a SharePoint view. The column is even visible in Excel 2003, but with an error: Invalid cell reference (I guess it's because Excel cannot find the column).

My farm runs SP 2010.

[Edit]. As requested, a bit more information:

As I said, the purpose of the custom field is to customize the UI of the native number field (providing a DropDown list to be more precise instead of a TextBox).

What I've done:

  1. The field definition:

    public class MyCustomField : SPFieldNumber
        public MyCustomField(SPFieldCollection fields, string fieldName)
            : base(fields, fieldName) { }
        public MyCustomField(SPFieldCollection fields, string typeName, string displayName)
            : base(fields, typeName, displayName) { }
        public override Microsoft.SharePoint.WebControls.BaseFieldControl FieldRenderingControl
                return new MyCustomFieldControl
                    FieldName = this.InternalName,
  2. The field declaration:

        <Field Name="TypeName">MyCustomField</Field>
        <Field Name="ParentType">Number</Field>
        <Field Name="TypeDisplayName">xxxxx</Field>
        <Field Name="TypeShortDescription">yyyyyy</Field>
        <Field Name="AllowBaseTypeRendering">TRUE</Field>
        <Field Name="UserCreatable">FALSE</Field>
        <Field Name="FieldTypeClass">$SharePoint.Type.3e27f5e8-348d-40c6-afcc-87306b2bb3ac.AssemblyQualifiedName$</Field>
        <Field Name="Sortable">TRUE</Field>
        <Field Name="Filterable">TRUE</Field>
  3. The control's behavior (especially the Value property:

    public class MyCustomFieldControl : BaseFieldControl, IDesignTimeHtmlProvider
        protected DropDownList ddlNumberOfPlaces;
        protected Label lblNumberOfPlaces;
        /* business rules removed from clarity */
        protected override void CreateChildControls()
            if (this.Field != null)
                ddlNumberOfPlaces = (DropDownList)this.TemplateContainer.FindControl("ddlNumberOfPlaces");
                lblNumberOfPlaces = (Label)this.TemplateContainer.FindControl("lblNumberOfPlaces");
                if (ControlMode == SPControlMode.Edit || ControlMode == SPControlMode.New) {
                    var maxNumberOfPlaces = MaximumNumberOfPlaces; // From my business rules
                    for (int i = 1; i <= maxNumberOfPlaces; i++) {
                    lblNumberOfPlaces.Visible = false;
                    ddlNumberOfPlaces.Visible = true;
                    lblNumberOfPlaces.Text = this.ItemFieldValue.ToString();
                    lblNumberOfPlaces.Visible = true;
                    ddlNumberOfPlaces.Visible = false;
        public override object Value
                int result;
                if (int.TryParse(ddlNumberOfPlaces.SelectedValue, out result))
                    return result;
                    return null;
                ddlNumberOfPlaces.SelectedValue = value.ToString();
                lblNumberOfPlaces.Text = value.ToString();
  4. And my simple control template

    <SharePoint:RenderingTemplate ID="MyCustomFieldControl" runat="server">
            <asp:DropDownList runat="server" ID="ddlNumberOfPlaces" EnableViewState="false" />
            <asp:Label runat="server" ID="lblNumberOfPlaces" EnableViewState="false" />
  • Can you provide a bit more detail about the custom field? What is the data type? Is there a formula involved? Or does the field just store a value? If so, what is it? Etc.
    – teylyn
    Commented Sep 27, 2013 at 9:59
  • @teylyn: updated my question to show how my control is build (I just renamed the control, and removed business code)
    – Steve B
    Commented Sep 27, 2013 at 10:16
  • Have you tried to add public override string TypeAsString { get { return "Number"; } } to your field class? If this helped, I could explain why :)) Commented Sep 27, 2013 at 12:08
  • Error: 'xxxx.MyCustomField.TypeAsString.get': cannot override inherited member 'Microsoft.SharePoint.SPField.TypeAsString.get' because it is not marked virtual, abstract, or override... it does not works
    – Steve B
    Commented Sep 27, 2013 at 12:22

1 Answer 1


It's a poor solution, but I ended to duplicate all fields that have issues:

  • Content Type name
  • my custom field

In a receiver (fortunately, I already have a receiver on my content type), I duplicate the value from my fields to their "text-compatible-with-old-excel" counterparts.

Tweaking a bit the show in display/edit/new forms, and views, it's nearly transparent for the users.

I put this in my yet-full box of hack in SharePoint projects

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