The Self-Taught Programmer

Recipes from real-world experience with asp.net.

Posts Tagged ‘Eval()

How To Avoid Null Reference Exceptions in an ASPX File When Dynamically Populating a GridView or ListView Control

leave a comment »

The situation:

You have a GridView control with a TemplateField in your ASPX page that is dynamically populated from a database. You of course use an Eval() statement to dynamically populate the TemplateField, but the db field is nullable (and in fact contains a null value), and when you run the page, you get an NullReferenceException because you are trying to bind to a null value.

This is your basic (simplified) code that is causing the error (because “Cost” is null):


<asp:GridView id="MyGridView"
	DataSourceID="MyDataSource1"
	Runat="Server">
	<Columns>
		<asp:TemplateField HeaderText="Cost">
			<ItemTemplate>
				<%# Eval("Cost") %>
			</ItemTemplate>
		</asp:TemplateField>
	</Columns
</asp:GridView>

Here is the fix: Add this method to your codebehind:


	protected string CheckNull(object objGrid)
	{
		if ( object.ReferenceEquals(objGrid, DBNull.Value) )
		{
			return "not available";
		}
		else if ( objGrid == null )
		{
			return "not available";
		}
		else
		{
			return objGrid.ToString();
		}
	}

You can change “not available” to any value you wish.

Then your template field should be changed to:


<%# CheckNull(Eval("Cost")) %>

And that should fix the issue.

Advertisements

Written by Jim McMullen

May 3, 2011 at 2:40 pm