what is the use of Eval() in asp.net

What is the use of Eval() in AS开发者_开发技巧P.NET?

While binding a databound control, you can evaluate a field of the row in your data source with eval() function.

For example you can add a column to your gridview like that :

<asp:BoundField DataField="YourFieldName" />

And alternatively, this is the way with eval :

<asp:TemplateField>
<ItemTemplate>
        <asp:Label ID="lbl" runat="server" Text='<%# Eval("YourFieldName") %>'>
        </asp:Label>
</ItemTemplate>
</asp:TemplateField>

It seems a little bit complex, but it's flexible, because you can set any property of the control with the eval() function :

<asp:TemplateField>
    <ItemTemplate>
        <asp:HyperLink ID="HyperLink1" runat="server" 
          NavigateUrl='<%# "ShowDetails.aspx?id="+Eval("Id") %>' 
          Text='<%# Eval("Text", "{0}") %>'></asp:HyperLink>
    </ItemTemplate>
</asp:TemplateField>

Eval is used to bind to an UI item that is setup to be read-only (eg: a label or a read-only text box), i.e., Eval is used for one way binding - for reading from a database into a UI field.

It is generally used for late-bound data (not known from start) and usually bound to the smallest part of the data-bound control that contains a whole record. The Eval method takes the name of a data field and returns a string containing the value of that field from the current record in the data source. You can supply an optional second parameter to specify a format for the returned string. The string format parameter uses the syntax defined for the Format method of the String class.

IrishChieftain didn't really address the question, so here's my take:

eval() is supposed to be used for data that is not known at run time. Whether that be user input (dangerous) or other sources.