ASP.NET Conditions in Markup Using Bound Data

AspDotNetDev

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Jan 12, 2012

CPOL

21771

C# version

C# Version (See Alternatives for VB.NET Version)

Have you ever tried to use an if statement in combination with data binding? You can't do this (can't use an if statement in this type of code block):

<%# if (Eval("YadaYada")) { %>

And you can't do this (can't data bind in this type of code block):

<% if (Eval("YadaYada")) { %>

So how do you combine these concepts? Basically, you can use a PlaceHolder with a Visible property set to a bound value (or the result of a condition based on a bound value). Anything (code blocks or markup) inside an invisible PlaceHolder will not be executed. Here is one way to go about that:

<%@ Page Language="C#" AutoEventWireup="true" %>
 
<script runat="server">
 
  // Sample class we can use for binding.
  public class Animal
  {
    public Boolean CanFly { get; set; }
    public String Description { get; set; }
  }
 
  // Setup binding in page load.
  protected void Page_Load(Object sender,System.EventArgs e)
  {
    rpItems.DataSource = new List<Animal> {
        new Animal {CanFly = false, Description = "Duck"},
        new Animal {CanFly = true, Description = "Duck"},
        new Animal {CanFly = false, Description = "Duck"},
        new Animal {CanFly = true, Description = "Goose!"}};
    rpItems.DataBind();
  }
 
</script>
 
<html>
<head>
    <title>Markup Conditions Using Bound Code Block</title>
</head>
<body>
    <form id="frmMain" runat="server">
 
      <!-- This is our data bound control. -->
      <asp:Repeater runat="server" ID="rpItems">
        <HeaderTemplate>
          <ul>
        </HeaderTemplate>
        <ItemTemplate>
 
          <!--  We use placeholder visibility to use different 
          markup depending on the bound value. -->
          <li>
            <asp:PlaceHolder runat="server" 
            Visible="<%# ((Animal)Container.DataItem).CanFly %>">
              <b>I can fly!</b>
            </asp:PlaceHolder>
            <asp:PlaceHolder runat="server" 
            Visible="<%# !((Animal)Container.DataItem).CanFly %>">
              I can't fly.
            </asp:PlaceHolder>
            <%# HttpUtility.HtmlEncode(((Animal)Container.DataItem).Description) %>
          </li>
 
        </ItemTemplate>
        <FooterTemplate>
          </ul>
        </FooterTemplate>
      </asp:Repeater>
 
    </form>
</body>
</html>

Alternatively, you can use the placeholders to set the value of a property or variable, which you can then use in code blocks that aren't data bound:

<%@ Page Language="C#" AutoEventWireup="true" %>
 
<script runat="server">
 
  // Sample class we can use for binding.
  public class Animal
  {
    public Boolean CanFly { get; set; }
    public String Description { get; set; }
  }
 
  // This property is used in the bound control.
  protected Boolean CanFlyTemp { get; set; }
 

  // Setup binding in page load.
  protected void Page_Load(Object sender,System.EventArgs e)
  {
    rpItems.DataSource = new List<Animal> {
        new Animal {CanFly = false, Description = "Duck"},
        new Animal {CanFly = true, Description = "Duck"},
        new Animal {CanFly = false, Description = "Duck"},
        new Animal {CanFly = true, Description = "Goose!"}};
    rpItems.DataBind();
  }
 
</script>
 
<html>
<head>
    <title>Markup Conditions Using Bound Code Block</title>
</head>
<body>
    <form id="frmMain" runat="server">
 
      <!-- This is our data bound control. -->
      <asp:Repeater runat="server" ID="rpItems">
        <HeaderTemplate>
          <ul>
        </HeaderTemplate>
        <ItemTemplate>
 
          <!-- We use placeholder visibility to 
          conditionally execute code based on a bound value. -->
          <% CanFlyTemp = false; %>
          <asp:PlaceHolder runat="server" 
          Visible="<%# ((Animal)Container.DataItem).CanFly %>">
            <% CanFlyTemp = true; %>
          </asp:PlaceHolder>
 
          <!-- Here we will use different markup 
          depending on the variable value set above. -->
          <li>
            <% if (CanFlyTemp) { %>
              <b>I can fly!</b>
            <% } else {%>
              I can't fly.
            <% }%>
            <%# HttpUtility.HtmlEncode(((Animal)Container.DataItem).Description) %>
          </li>
 
        </ItemTemplate>
        <FooterTemplate>
          </ul>
        </FooterTemplate>
      </asp:Repeater>
 
    </form>
</body>
</html>