A simple asp:Repeater replacement for simple needs

How many times have you had to parse through a collection of objects, outputting nothing more than a comma-delimited list of items in the result set. Typically, you’ll do this:

<asp :repeater runat="server">
	<itemtemplate>Eval("Name")</itemtemplate>
	<separatortemplate>, </separatortemplate>
</asp>

If you were parsing a list of states, it might look like this:

Alabama, Alaska, Arizona, Arkansas

There’s an easier way to handle these simple needs: create a CollectionToString() method. This method would accept an IEnumerable and, using reflection, read a property and return a delimited string. Of course, you choose the property and delimiter.

Note that we have two versions of this method: one which accepts an IEnumerable, the other which accepts an object. This is done to avoid the necessary typecasting in your code, since Eval() returns everything as an object.

public static string CollectionToString(IEnumerable collection, string property, string delimiter)
{
	IEnumerator enumerator = collection.GetEnumerator();
	if (enumerator == null || enumerator.MoveNext() == false)
		return String.Empty;

	Type type = enumerator.Current.GetType();
	PropertyInfo propInfo = type.GetProperty(property);
	if (propInfo == null)
		throw new Exception(String.Format("Property '{0}' not found in collection", property));

	StringBuilder output = new StringBuilder();
	output.Append(propInfo.GetValue(enumerator.Current, null).ToString());

	while (enumerator.MoveNext())
	{
		output.Append(delimiter);
		output.Append(propInfo.GetValue(enumerator.Current, null).ToString());
	}

	return output.ToString();
}

public static string CollectionToString(object collection, string property, string delimiter)
{
	return CollectionToString(collection as IEnumerable, property, delimiter);
}

This method — which I typically apply to a StringHelper class whose namespace is added to my web.config (more on that another day) — can replace the Repeater code above as follows.

<!-- you must first expose the collection to the ASPX page as a public property -->
< %= StringHelper.CollectionToString("ListOfStates", "Name", ", ") %>

A similar method could be added to a helper class in Castle MonoRail to do the same without using foreach loops in your view.