Dynamically add a field to a collection in c#?

Question

I have some basic dropdownlist databinding code. I need to modify the datasource at Runtime and insert a new field.

  ddlPrimaryCarrier.DataSource = FinancialInstitutions;
            ddlPrimaryCarrier.DataValueField = "EntityCode";
            ddlPrimaryCarrier.DataTextField = "EntityNameDesc";
            ddlPrimaryCarrier.DataBind();

I actually want to add a field to the collection that is a formatted string of the description and the code. Like...

var newField = string.Format("({0}) - {1}", "EntityCode", "EntityNameDesc");

then

ddlPrimaryCarrier.DataTextField = "newField";

What is the correct way to do this? Can I loop through the exisiting collection and create a new list of anonymous types with the field I need? Anyone have any examples of how to do that?

Thanks, ~ck in San Diego

Answer 1

Assuming that FinancialInstitutions is a collection of FinancialInstitution objects, add a new property to your FinancialInstitution class :

public string DisplayName
{
    get { return string.Format("({0}) - {1}", EntityCode, EntityNameDesc);
}

If it is a DataTable, you can add a computed column :

FinancialInstitutions.Columns.Add("DisplayName", typeof(string), "'(' + EntityCode + ') - ' + EntityNameDesc");

In both cases, set the ComboBox's DisplayMember to "DisplayName"

Answer 2

The simplest approach here is to add a property to the type. If this is generated (perhaps EF etc) then use a partial class:

namespace Whatever {
    partial class FinancialInstitution {
        public string EntityCaption {
            get {return "(" + EntityCode + ") - " + EntityNameDesc;
        }
    }
}

If this is a DataTable, you could add a computed column. If this is a type outside of your control, it is possible to do this (directly to the type) using a custom type-descriptor (via TypeDescriptionProvider), but it is very hard. I would instead prefer to encapsulate the instance, adding pass-thru properties that mimic the encapsulated class, and adding the new one:

class MyShim {
    private readonly FinancialInstitution inner;
    public MyShim(FinancialInstitution inner) {this.inner = inner;}
    public string EntityCode { get {return inner.EntityCode;}}
    public string EntityNameDesc { get {return inner.EntityNameDesc;}}
    public string EntityCaption {
        get {return "(" + EntityCode + ") - " + EntityNameDesc;
    }
}

and bind to the shims instead.