Using a const string as ID for a ASP.net Webforms Control

Question

You know if you're working with Repeater Controls you're not able to access the controls the generic way (as far as I know). So we try to use const strings for most situations we have to work with strings in C#.

So I've made a class with const strings. They define the ID names of the Controls inside a repeater. That makes it possible to access the controls in a more generic way than using the plain strings in code. Example:

public class FormularRepeaterFieldIDs
{
    public const string RubrikLiteral = "BuchungRubrikLiteral";
    public const string RubrikDropDownList = "BuchungRubrikList";
    public const string RubrikIdHiddenField = "BuchungRubrikIdHidden";
}

Which enables access like this (of course you could make a easier access wrapper for this):

                Literal rubrikLiteral = (Literal)e.Item.FindControl(TimeExpressHelper.FormularRepeaterFieldIDs.RubrikLiteral);
                rubrikLiteral.Visible = false;

Now I would also be cool to use the predefined IDs in Webforms Frontend code. It looks this at the moment:

<asp:Literal ID="BuchungRubrikLiteral" Text='<%#Eval("strRubrik")%>' runat="server" />

Would it be possible to make something like this?

<asp:Literal ID="<% FormularRepeaterFieldIDs.RubrikLiteral %>" Text='<%#Eval("strRubrik")%>' runat="server" />

@nunespascal Not really. But It would be nice to have all things together. I'm just asking ;) — René Stalder
– René Stalder, Commented Jun 22, 2012 at 9:28
ID's in asp.net front can't contains "'|','.',',','@','#','%','^','&','*',mathematic operators" I don't really know is this posible but try fullNamespace.FormularRepeaterFieldIDs.RubrikLiteral.GetType().Name.Replace('.','_'); — Harry89pl
– Harry89pl, Commented Jun 22, 2012 at 9:32
@harry180 Nope still doesn't work. Not valid identifier. So I think it's not possible without using code behind. — René Stalder
– René Stalder, Commented Jun 22, 2012 at 9:36

Mark Brackett · Accepted Answer · 2012-06-27 08:32:22Z

1

You could probably make this work with a custom ExpressionBuilder. Something like:

  <asp:Literal ID="<%$ Const:FormularRepeaterFieldIDs.BuchungRubrik" 
     Text='<%#Eval("strRubrik")%>' runat="server" />

with a ExpressionBuilder that uses Reflection and/or a CodeSnippetExpression to read the value:

  class ConstExpressionBuilder : ExpressionBuilder {
       override bool SupportsEvaluate { get { return true; } }

       override CodeExpression GetCodeExpression(BoundPropertyEntry entry, ...) {
           return new CodeSnippetExpression(entry.Expression);
       }

       override object EvaluateExpression(BoundPropertyEntry entry, ...) {
           var splitExpression = entry.Expression.Split('.');
           var fieldName = splitExpression.Last();
           var typeName = entry.Expression.Substring(entry.Expression.Length - fieldName.Length - 1);
           var type = Type.GetType(typeName);
           return type.GetField(fieldName).GetValue(null);
       }
  }

and a web.config to register it to handle the Const prefix:

  <expressionBuilders>
     <add expressionPrefix="Const" type="ConstExpressionBuilder" />
  </expressionBuilders>

Or, you could take advantage of the existing ResourceExpressionBuilder, and make them resources instead of constants.

answered Jun 27, 2012 at 8:32

Mark Brackett

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René Stalder Over a year ago

That sounds nice. I'm not going to try this one day. I give you that point. I'm sure this works. About resources: I already thought this could be a good way. Because we use const for such definitions I asked for I didn't use resources that way, but you're right, that would work as well.

Harry89pl · Accepted Answer · 2012-06-22 10:52:35Z

0

You can try

<div runat="server" id="container">
<% 
   List<string> listOfIds = new List<string>{FormularRepeaterFieldIDs.RubrikLiteral};
   foreach(var i in listOfIds.Count)
   {
      var l = new label();
      l.ID = listOfIds[i];
      container.Controls.Add(l);
   }
%>
</div>

answered Jun 22, 2012 at 10:52

Harry89pl

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1 Comment

René Stalder Over a year ago

Yeah of course I could. But thats actually the same doing it in code behind. I'm just searching for a really short way assigning a controls ID in frontend with help of a predefined const.

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