Question

嗨，当我从下拉列表中选择“其他”时，我想将我的文本框和按钮可见性设置为true。我该怎么做？

我的代码隐藏

    using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Xml;

public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {
        TextBox1.Visible = false;
        Button1.Visible = false;
        TextBox2.Visible = false;
       Button2.Visible = false;
        if (!IsPostBack)
        {
            PopulateDDLFromXMLFile();
        }
    }
    protected void TextBox1_TextChanged(object sender, EventArgs e)
    {

    }

    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {

        if (DropDownList1.SelectedValue == "Others")
        {
            TextBox1.Visible = true;
            Button1.Visible = true;
        }

    }
    protected void TextBox3_TextChanged(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {

    }
    protected void TextBox2_TextChanged(object sender, EventArgs e)
    {
        if (DropDownList2.SelectedValue == "Others")
        {
            TextBox2.Visible = true;
            Button2.Visible = true;
        }
    }
    protected void XmlDataSource1_Transforming(object sender, EventArgs e)
    {

    }
    protected void TextBox3_TextChanged1(object sender, EventArgs e)
    {

    }
    public void PopulateDDLFromXMLFile()
    {
        DataSet ds = new DataSet();
        ds.ReadXml(MapPath("~/App_Data/builderemail.xml"));

        //get the dataview of table "Country", which is default table name
        DataView dv = ds.Tables["builder"].DefaultView;
        DataView dw = ds.Tables["manager"].DefaultView;
        //or we can use:
        //DataView dv = ds.Tables[0].DefaultView;

        //Now sort the DataView vy column name "Name"
        dv.Sort = "value";

        //now define datatext field and datavalue field of dropdownlist
        DropDownList1.DataTextField = "value";
        DropDownList1.DataValueField = "ID";
        DropDownList2.DataTextField = "value";
        DropDownList2.DataValueField = "ID";

        //now bind the dropdownlist to the dataview
        DropDownList1.DataSource = dv;
        DropDownList1.DataBind();
        DropDownList2.DataSource = dw;
        DropDownList2.DataBind();

    }
}

我的xml文件：

<?xml version="1.0" encoding="utf-8"?>
<email>
  <builderemail>
    <builder>
      <id>1</id>
      <value>builder@xyz.com</value>
    </builder>
    <builder>
      <id>2</id>
      <value>Others</value>
    </builder>
  </builderemail>
  <manageremail>
    <manager>
      <id>1</id>
      <value>manager@xyz.com</value>
    </manager>
    <manager>
      <id>2</id>
      <value>Others</value>
    </manager>
    </manageremail>
</email>

Answer 1

The issue is not with the Visible state toggle code in Page_Load, but it is advisable as suggested by @Shoban, to put the Visible state toggle code inside

if(!IsPostback) { //set the visible state to false; }

或者更好地设置标记中每个控件的Visible属性。

<asp:TextBox ID= TextBox1  runat="server" Visible="false">
    </asp:TextBox>

但问题在于以下方法：

Is it firing? If not enable the viewstate on your page / on the dropdownlist If it is firing, the code you ve written will not work. Because, the SelectedValue is mapped to "id" field in your Populate method

DropDownList1.DataValueField = "id";

但是在下面的代码中，您正在检查DataTextField（“value”列）

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {

        if (DropDownList1.SelectedValue == "Others")
        {
            TextBox1.Visible = true;
            Button1.Visible = true;
        }

    }

修改检查：

if (DropDownList1.SelectedItem.Text.Equals("Others", StringComparison.Ordinal))
{
    TextBox1.Visible = true;
}

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