可以从字面上删除标签项目

我有以下代码

namespace WebApplication3
{
    public partial class WebForm2 : System.Web.UI.Page
    {
        class Customer
        {
            public Customer(int id, string fName)
            {
                ID = id;
                FirstName = fName;
            }
            public int ID { get; set; }
            public string FirstName { get; set; }
        }
        private List<Customer> GetCustomerNames()
        {
            // Add Customers to list - this is essentially coming from a database
            List<Customer> Names = new List<Customer>();
            Names.Add(new Customer(1, "Name 1"));
            Names.Add(new Customer(2, "Name 2"));
            Names.Add(new Customer(3, "Name 3"));
            Names.Add(new Customer(4, "Name 4"));
            return Names;
        }
        private void DropdownNames()
        {
            // Set the dropdown
            ddlName.DataSource = GetCustomerNames();
            ddlName.DataTextField = "FirstName";
            ddlName.DataValueField = "ID";
            ddlName.DataBind();
        }
        private void SetNameHTML(List<Customer> Names)
        {
            // The below code would set the literal control with the values coming from the list along with custom span so the design would be correct
            Int32 Count = 0;
            lit1.Text = string.Empty;
            foreach (Customer c in Names)
            {
                if (Count == 0)
                {
                    // IF first element then set active class so correct style is applied
                    lit1.Text += string.Format("<span class='square active' ID='spName' runat='server' data-value='{0}'>{1}</span> <br />", c.FirstName, c.ID);
                    spName.InnerText = c.FirstName;
                }
                else
                {
                    // Other non selected items - Note no active listed in the class
                    lit1.Text += string.Format("<span class='square' ID='spName' runat='server' data-value='{0}'>{1}</span> <br />", c.FirstName, c.ID);
                }
                Count += 1;
            }
        }
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                DropdownNames();
                SetNameHTML(GetCustomerNames());
            }
        }
        protected void ddlName_SelectedIndexChanged(object sender, EventArgs e)
        {
            // Get customer names again as the list would be empty if the SetNameHTML is removed
            var CustomerNames = GetCustomerNames();
            SetNameHTML(CustomerNames);
            // Get a single customer to set the correct class (square active)
            var CustName = CustomerNames.Where(cid => cid.ID == Convert.ToInt32(ddlName.SelectedValue)).FirstOrDefault();
            spName.InnerText = ddlName.SelectedItem.Text;
            // += on lit1.Text so that the span list is not empty. 
            // If i remove the lin SetNameHTML(CustomerNames); above then the list is empty
            lit1.Text = string.Format("<span class='square active' ID='spName' runat='server' data-value='{0}'>{1}</span> <br />", CustName.FirstName, CustName.ID);
        }
    }
}

aspx代码

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            <span class="info" runat="server" id="spName"></span>
            <asp:DropDownList ID="ddlName" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddlName_SelectedIndexChanged"></asp:DropDownList>
            <br />
            <div class="squares">
                <asp:Literal ID="lit1" runat="server"></asp:Literal>
            </div>
        </div>
    </form>
</body>
</html>

我正在使用文字控件，因此我可以根据找到的名称数量添加相关跨度。请注意，我将大部分CSS JS剥离出来，这就是为什么看起来很朴素的原因。

当我从下拉列表中选择一个项目会再次添加项目（如果您运行上述代码，您将知道我的意思是什么）

请注意我的评论以及为什么我做了我的评论。

HER是页面加载何时的视图来源，然后选择一个项目

加载

<div class="squares">
<span class='square active' ID='spName' runat='server' data-value='Name 1'>1</span> <br />
<span class='square' ID='spName' runat='server' data-value='Name 2'>2</span> <br />
<span class='square' ID='spName' runat='server' data-value='Name 3'>3</span> <br />
<span class='square' ID='spName' runat='server' data-value='Name 4'>4</span> <br />
            </div>

选定的第一个项目

<div class="squares">
<span class='square active' ID='spName' runat='server' data-value='Name 1'>1</span> <br />
<span class='square' ID='spName' runat='server' data-value='Name 2'>2</span> <br />
<span class='square' ID='spName' runat='server' data-value='Name 3'>3</span> <br />
<span class='square' ID='spName' runat='server' data-value='Name 4'>4</span> <br />
<span class='square active' ID='spName' runat='server' data-value='Name 2'>2</span> <br />
            </div>

我知道为什么会发生这种情况，但我不确定该怎么做。我想做的不是再次将所选项目添加到列表中，但是由于我使用文字控件，我不知道如何删除它，或者是否有更好的方法可以解决？

您可以用占位符替换文字控制：

<asp:PlaceHolder ID="ph1" runat="server" />

并在其中添加ASP.NET标签控件，它们在HTML输出中呈现为span元素，或ASP.NET面板控件，将其呈现为div Elements。

。

这样，您将使用控件而不是在字面上插入RAW HTML代码，这更难管理。

update

必须将新标签添加到每个回发的占位符，而不是在if (!IsPostBack)条件块中。每个ID也必须是唯一的（或者您可以将ID属性留为空）。我之所以提及它，是因为我在标记样本中看到了几个具有ID spname的span元素。

在简单的情况下，看起来像这样：

private int labelSuffix = 0;
protected void Page_Load(object sender, EventArgs e)
{
    Label lbl = new Label();
    lbl.ID = string.Format("span_{0}", labelSuffix++);
    lbl.Attributes.Add("data-value", "Name 1");
    lbl.CssClass = "square";
    lbl.Text = "1";
    ph1.Controls.Add(lbl);
    ...
}

然后可以在另一个事件处理程序中检索标签：

protected void btnPostBack_Click(object sender, EventArgs e)
{
    // By the ID of the control
    Label lbl = ph1.FindControl("MyLabel") as Label;
    lbl.Text = "With some new text";
    // Or by looping on the controls collection
    foreach (Label lbl in ph1.Controls)
    {
        lbl.Text = "And another text";
    }
}

添加值（或在更改事件上）检查是否不存在

if (!ddlName.Items.Contains("ValueToAdd"))
{//add value in dropdown list}

希望这有帮助

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