ASP.NET在绑定时使用条件表达式

ASP.NET在绑定时使用条件表达式
Asp.net2.0不支持在数据绑定时的条件表达式。Asp.net 4.0已经平滑地解决这个问题，不用修改代码。
下面让我们来看一个简单的ASP.NET数据绑定场景，有这么一个Repeater：
```
   1:      <asp:Repeater runat="server" ID="itemsList">
```
```
   2:          <HeaderTemplate>
```
```
   3:              <table border="1" cellspacing="0" cellpadding="5">
```
```
   4:          </HeaderTemplate>
```
```
   5:          <ItemTemplate>
```
```
   6:              <tr>
```
```
   7:                  <td align="right">
```
```
   8:                      <%# Container.ItemIndex + 1 %>.
```
```
   9:                  </td>
```
```
  10:                  <td>
```
```
  11:                      <%# Eval("Title") %>
```
```
  12:                  </td>
```
```
  13:              </tr>
```
```
  14:          </ItemTemplate>
```
```
  15:          <FooterTemplate>
```
```
  16:              </table>
```
```
  17:          </FooterTemplate>
```
```
  18:      </asp:Repeater>
```
然后后端的cs:
```
   1:     protected void Page_Load(object sender, EventArgs e)
```
```
   2:          {
```
```
   3:              var items = new[] { 
```
```
   4:                      new { Id = 1, Title = "Headline 1" },
```
```
   5:                      new { Id = 2, Title = "Headline 2" },
```
```
   6:                      new { Id = 2, Title = "Headline 3" },
```
```
   7:                      new { Id = 2, Title = "Headline 4" },
```
```
   8:                      new { Id = 2, Title = "Headline 5" }
```
```
   9:                  };
```
```
  10:              itemsList.DataSource = items;
```
```
  11:              itemsList.DataBind();
```
```
  12:          }
```
当我们需要判断绑定时数据行，我们需要Create这么一个类似的方法或函数：
```
   1:          /// <summary>
```
```
   2:          /// Iifs the specified condition.
```
```
   3:          /// </summary>
```
```
   4:          /// <param name="condition">if set to <c>true</c> [condition].</param>
```
```
   5:          /// <param name="trueResult">The true result.</param>
```
```
   6:          /// <param name="falseResult">The false result.</param>
```
```
   7:          /// <returns></returns>
```
```
   8:          protected object Iif(bool condition, object trueResult, object falseResult)
```
```
   9:          {
```
```
  10:               return condition ? trueResult : falseResult;
```
```
  11:          } 
```
然后在ASPX中使用它：
```
   1:  <asp:Repeater runat="server" ID="Repeater1">
```
```
   2:    <HeaderTemplate>
```
```
   3:      <table border="1" cellspacing="0" cellpadding="5">
```
```
   4:      </HeaderTemplate>
```
```
   5:    <ItemTemplate>
```
```
   6:      <tr style='background-color: <%# Iif(Container.ItemIndex % 2==0, "white", "whitesmoke") %>'>
```
```
   7:        <td align="right">
```
```
   8:          <%# Container.ItemIndex + 1 %>.</td>
```
```
   9:        <td>
```
```
  10:          <%# Eval("Title") %></td>
```
```
  11:      </tr>
```
```
  12:    </ItemTemplate>
```
```
  13:    <FooterTemplate>
```
```
  14:      </table>
```
```
  15:    </FooterTemplate>
```
```
  16:  </asp:Repeater>
```
这是在模仿VB中的IIF函数。到了ASP.NET 4.0中，我们可以直接这么写了：
```
   1:  <asp:Repeater runat="server" ID="Repeater2">
```
```
   2:    <HeaderTemplate>
```
```
   3:      <table border="1" cellspacing="0" cellpadding="5">
```
```
   4:      </HeaderTemplate>
```
```
   5:    <ItemTemplate>
```
```
   6:      <tr style='background-color:<%# Container.ItemIndex % 2==0 ? "white" : "whitesmoke" %>'>
```
```
   7:        <td align="right">
```
```
   8:          <%# Container.ItemIndex + 1 %>.</td>
```
```
   9:        <td>
```
```
  10:          <%# Eval("Title") %></td>
```
```
  11:      </tr>
```
```
  12:    </ItemTemplate>
```
```
  13:    <FooterTemplate>
```
```
  14:      </table>
```
```
  15:    </FooterTemplate>
```
```
  16:  </asp:Repeater>
```
好了，这个演示是基于ASP.NET WebForm 数据绑定时条件表达式的实现。希望这篇POST对您有帮助！

Author: Petter Liu http://wintersun.cnblogs.com
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原文地址：https://www.cnblogs.com/wintersun/p/1714827.html