Dropdownlist onselectedindexchanged事件无效 [英] Dropdownlist onselectedindexchanged event is not working

问题描述

在页面加载时，国家/地区下拉列表已绑定且工作正常但在我选择国家/地区后，状态下拉列表中没有状态绑定。



我的尝试：

 ------------ ----------前端----------------------------- 
< asp：DropDownList ID =   ddlcountry runat =   server OnSelectedIndexChanged =   ddlcountry_SelectedIndexChanged AutoPostBack =   true CssClass =  < span class =code-string> form-control ddl >  < /   asp：DropDownList  >  
 
< asp：DropDownList ID = < span class =code-string>  ddlstate runat =   server AutoPostBack =   true CssClass =   form-control ddl >  < /   asp：DropDownList  >  
 
 --------------------------------背后的代码---------- -------------------- 
 
  protected   void  Page_Load（ object  sender，EventArgs e）
 {
  if （con.State == ConnectionState.Closed）
 {
 con.Open（）; 
} 
  if （！Page.IsPostBack）
 {
 getcountry（）; 
} 
} 
 受保护  void  getcountry（）
 {
 尝试 
 {
 da =  new  SqlDataAdapter（< span class =code-string>  select * from get_country，con）; 
 ds =  new  DataSet（）; 
 da.Fill（ds）; 
 ddlcountry.DataSource = ds; 
 ddlcountry.DataTextField =   conname; 
 ddlcountry.DataValueField =   conid; 
 ddlcountry.DataBind（）; 
 ddlcountry.Items.Insert（ 0 ， new  ListItem（   - 选择 - ，  0））; 
 ddlstate.Items.Insert（ 0 ， new  ListItem（   - 选择 - ，  0））; 
} 
  catch （例外情况）
 {
 Response.Write（ 发生错误： + ex.Message.ToString（））; 
} 
 最后 
 {
 con.Close（）; 
} 
} 
 受保护  void  ddlcountry_SelectedIndexChanged（ object  sender，EventArgs e）
 {
  try  
 {
 < span class =code-keyword> int  conid = Convert.ToInt32（ddlcountry.SelectedItem.Value.ToString（））; 
 da =  new  SqlDataAdapter（  select stateid ，来自get_state的statename，其中conid = + conid，con）; 
 ds =  new  DataSet（）; 
 da.Fill（ds）; 
 ddlstate.DataSource = ds; 
 ddlstate.DataTextField =   statename; 
 ddlstate.DataValueField =   stateid; 
 ddlstate.DataBind（）; 
 ddlstate.Items.Insert（ 0 ， new  ListItem（  ---选择状态---，  0\" ））; 
  if （ddlstate.SelectedValue ==   0）
 {
 ddlcity.Items.Clear（）; 
 ddlcity.Items.Insert（ 0 ， new  ListItem（  ---选择City ---，  0\" ））; 
} 
} 
  catch （例外情况）
 {
 Response.Write（ 错误： + ex.Message.ToString（））; 
} 
 最后 
 {
 con.Close（）; 
} 
} 

解决方案

基于评论代码

 ddlstate.Items.Insert（ 0 ， new  ListItem（  ---选择状态---，  0））;  //  第1行 
  if （ddlstate.SelectedValue ==   0） / /  第2行 
 {
 ddlcity.Items.Clear（）;  //  第3行 
 ddlcity.Items.Insert（ 0 ， new  ListItem（  ---选择城市---，  0））; 
} 

第1行中的
您在第0个索引处插入一个值，默认情况下会选择这个值
第2行中
您正在检查所选值是否等于0，当然它将仅为0，它将在第3行中传递条件

它将清除ddlcity中的所有项目

最终你的ddlstate将是空的，



解决方案：

 < span class =code-keyword> if （ ddlCountry  .SelectedValue ==   0） //  将州改为国家 

on page load the country dropdownlist is bind and working fine but after when i select the country than no state bind in state dropdownlist.

What I have tried:

 ----------------------front end-----------------------------
<asp:DropDownList ID="ddlcountry" runat="server" OnSelectedIndexChanged="ddlcountry_SelectedIndexChanged" AutoPostBack="true" CssClass="form-control ddl"></asp:DropDownList>
 
<asp:DropDownList ID="ddlstate" runat="server" AutoPostBack="true" CssClass="form-control ddl"></asp:DropDownList> 
 
--------------------------------code behind------------------------------ 
 
protected void Page_Load(object sender, EventArgs e)
{
if (con.State == ConnectionState.Closed)
{
con.Open();
}
if (!Page.IsPostBack)
{
getcountry();
}
}
protected void getcountry()
{
try
{
da = new SqlDataAdapter("select * from get_country", con);
ds = new DataSet();
da.Fill(ds);
ddlcountry.DataSource = ds;
ddlcountry.DataTextField = "conname";
ddlcountry.DataValueField = "conid";
ddlcountry.DataBind();
ddlcountry.Items.Insert(0, new ListItem("--Select--", "0"));
ddlstate.Items.Insert(0, new ListItem("--Select--", "0"));
}
catch (Exception ex)
{
Response.Write("error occurd :" + ex.Message.ToString());
}
finally
{
con.Close();
}
}
protected void ddlcountry_SelectedIndexChanged(object sender, EventArgs e)
{
try
{
int conid = Convert.ToInt32(ddlcountry.SelectedItem.Value.ToString());
da = new SqlDataAdapter("select stateid,statename from get_state where conid=" + conid, con);
ds = new DataSet();
da.Fill(ds);
ddlstate.DataSource = ds;
ddlstate.DataTextField = "statename";
ddlstate.DataValueField = "stateid";
ddlstate.DataBind();
ddlstate.Items.Insert(0, new ListItem("---Select State---", "0"));
if (ddlstate.SelectedValue == "0")
{
ddlcity.Items.Clear();
ddlcity.Items.Insert(0,new ListItem("---Select City---","0"));
}
}
catch(Exception ex)
{
Response.Write("error occurd :" + ex.Message.ToString());
}
finally
{
con.Close();
}
}

解决方案

based on the code from Comments

ddlstate.Items.Insert(0, new ListItem("---Select State---", "0")); // line 1
if (ddlstate.SelectedValue == "0")  // line 2
{
ddlcity.Items.Clear();  // line 3
ddlcity.Items.Insert(0,new ListItem("---Select City---","0"));
}

in line 1 you are inserting a value at 0th index, which will be selected by default
in line 2 you are checking the selected value is equals 0, of course it will be 0 only, it will pass inside the condition
in line 3 it will clear all the items in ddlcity
ultimately your ddlstate will be empty,

Solution:

if (ddlCountry.SelectedValue == "0") // change state to country

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