how to handle nulls in a RadioButtonList

My webform RadioButtonList is bound to a column from a Sql Server dataSource. The radioButtonList is in a formView which starts up in edit mode. My question is how to handle null values because the only way I could get the page to come up when the columnn value is null is to have an item in the radio list which is setup for nulls such as, "Unknown" in the Text property and -1 in the value property. I understand that the RadioButtonList control is supposed to default to nulls which means that nothing in the radio list is selected - this is the behavior that I want, but I get the error below complaining that null (-1) is not valid because it does not exist as a valid value in the radio list: I have tried -1, '', etc. with no success.

'RadioButtonList2' has a SelectedValue which is invalid because it does not exist in the list of items.
Parameter name: value

How should I handle nulls at page startup?

Thanks.

While setting SelectedValue = null will normally allow no default selection for the RadioButtonList control, trying to set it to null in binding (using either Eval or Bind) doesn't work and throws an exception. Going through a method, however, seems to work as follows:

[ASPX]

<ItemTemplate>

<asp:RadioButtonListID="RadioButtonList1"runat="server"SelectedValue='<%# myFunc(Eval("NumValue").ToString()) %>'>

<asp:ListItemValue="1"Text="Item 001"></asp:ListItem>

<asp:ListItemValue="2"Text="Item 002"></asp:ListItem>

<asp:ListItemValue="3"Text="Item 003"></asp:ListItem>

<asp:ListItemValue="4"Text="Item 004"></asp:ListItem>

<asp:ListItemValue="5"Text="Item 005"></asp:ListItem>

</asp:RadioButtonList>

</ItemTemplate>

[code-behind: C#]

publicstring myFunc(string val)

{

if (val =="")

returnnull;

else

return val;

}

Thank you, the myFunc worked great for handling nulls, But it caused another problem with the update statement. My update statement no longer works because it has lost the identity of the bound variable somehow.

The default SelectedValue works fine:

aspx:

SelectedValue='<%# Bind("myField") %>'

UpdateCommand="update myTable setmyField=@.myField

But with your custom SelectedValue code I get the error at the bottom:

SelectedValue='<%# myFunc(Eval("r1").ToString()) %>'

UpdateCommand="update myTable setmyField=@.myField

here is the error:

Must declare the variable'@.myField'.

[SqlException (0x80131904): Must declare the variable'@.myField'.]

The customization to SelectedValue caused this, any idea why?

Thanks.

I can see why this would be an issue when trying to update since it deviates from the binding expected by the framework. Interesting situation you have here. I'll have to look into this before giving you an answer. I wouldn't be surprised if someone already faced such situation and resolved it.
Thanks. I am appreciative of your help.
I tried to see if there's a workaround for this issue, but I'm afraid there isn't as far as I can see. I thought that there might be a way to bind a NULL value into SelectedValue property (which can be done if a direct null value is assigned), but when binding to a table column, it rejects it for some reason. This problem/behavior may be related to the fact that RadioButtonList isn't meant to provide an option for "no selection" (i.e. once a selection is made, you cannot go back to a no-selection state), although the starting point allows no selection state. Perhaps the DropDownList control serves your purpose better since you can have a default value that represents no selection. Another option might be to add another item for your RadioButtonList that represents no selection and default what would have been null value to that choice. Sorry I don't have a better news for you.

Here's another way to handle this. Create a user control with your RadioButtonList in it, and create a property in it called SelectedValue such as following:

public string SelectedValue
{
get
{
return RadioButtonList1.SelectedValue;
}
set
{
if (value != "")
RadioButtonList1.SelectedVAlue = value;
}
}

This way you conditionally avoid setting the RadioButtonList value when it's null. Then you can happily use the SelectedValue='<%# Bind("FieldName") %>' syntax in your user control tag declaration.