How to store value of data binding expression into variable - asp.net

Question

I need to access the value of a bound item several times in a template. Right now my ListView template looks like this:
<asp:ListView ID="ListView1" runat="server" ItemPlaceholderID="plc"><br/>
<ItemTemplate><br/>
<input type="radio" class="myrating<%# DataBinder.Eval(Container.DataItem, "Day")%>" value="3" /><br/>
<input type="radio" class="myrating<%# DataBinder.Eval(Container.DataItem, "Day")%>" value="4" /><br/>
</ItemTemplate><br/>
<LayoutTemplate><br/>
<div id="plc" runat="server"><br/>
</div><br/>
</LayoutTemplate><br/>
<EmptyDataTemplate><br/>
No data</EmptyDataTemplate><br/>
</asp:ListView><br/>
Under certain conditions I may have dozens of radio button so repeatedly calling <%# DataBinder.Eval(Container.DataItem, "Day")%> seems to be inefficient.
I would like to assign the value of that expression to a variable and then use this variable instead so my template would look something like this
<ItemTemplate><br />
<%String ClassName = "myrating" + <%# DataBinder.Eval(Container.DataItem, "Day")%><br />
<input type="radio" class="<%=ClassName %>" value="3" /><br />
<input type="radio" class="<%="ClassName" value="4" /><br />
</ItemTemplate><br />
This example doesn't compile but I hope you are getting the idea.

Answer 1

You can give your page a public variable MyRating.
Now you can assign the variable in the expression binding Syntax:
<ItemTemplate>
<%# MyRating = "myrating" + <%# Eval(Container.DataItem, "Day")%>
//Use the variable inside the binding(!) block
<%#MyRating
</ItemTemplate>
I usually bind to lists of view-objects. That way I can access view properties directly.
<ItemTemplate>
<%# MyType = (MyType)Container.DataItem
<%# MyRating.Average %>
<%# MyRating.Count %>
</ItemTemplate>
Hope this helps :-)

Answer 2

You can use OnItemDataBount event and work with DataItem as with variable there.

Answer 3

I personally consider setting HTML element values in the OnItemDataBound event to be messier than in the ASP code. I also didn't like setting the variable value using a data-binding expression since it seems to cause the value to be output in the HTML.
Here's a similar way to do it based on the other answers:
1. Create a protected field in the code-behind to use as your variable.
protected string className;
2. Use a data-binding expression to assign to the variable.
<asp:Literal runat="server" Visible="false" Text="<%# className = "myrating" + DataBinder.Eval(Container.DataItem, "Day") %>" />
Make sure to do this inside the hidden server-side tag so that the result of the expression does not appear in the resulting HTML.
3. Use the variable inside data-binding expressions in the ASP code.
<ItemTemplate><br />
<input type="radio" class="<%# className %>" value="3" /><br />
<input type="radio" class="<%# className %>" value="4" /><br />
</ItemTemplate><br />
Make sure to use data-binding expressions to access the variable. Other expression types only seem to see the default value of the variable.
I think the main disadvantage of this approach is the use of the field, which would ideally be scoped to the ItemTemplate element.

Answer 4

You can define public/protected variables in the code-behind and assign those in data binding expressions.
If you don't have access to the code-behind (e.g. when you are modifying the markup of a compiled application), you can declare variables in a script block set to run on server, e.g.:
<script runat="server">
YourNamespace.Rating current;
</script>
Then in your control's binding templates:
<HeaderTemplate>
<%# (current = (YourNamespace.Rating)Eval("Day")) == null ? "" : "" %>
</HeaderTemplate>
Put it in the HeaderTemplate if you only want it to get executed once per databinding.
The == null ? "" : ""-part, is to prevent any generated cruft html (e.g. the ToString value of the assigned value), from being rendered in the browser.