How to use the DropDownList s SelectedIndexChanged event

Question

I have two DropDownLists in my webform and when I select a value in the first dropdownlist  I would like a related value to be automatically selected in the second dropdownlist   This is what I currently have        lt table gt              lt tr gt               lt td gt                   lt asp Label ID  lbmanu  runat  server  Text  Furniture Manufacturer                         gt  lt  asp Label gt               lt  td gt               lt td gt                   lt asp DropDownList ID  ddmanu  runat  server                       DataSourceID  Sql fur model manu                          DataTextField  manufacturer  DataValueField  manufacturer                       onselectedindexchanged  ddmanu SelectedIndexChanged  gt                   lt  asp DropDownList gt                   lt asp SqlDataSource ID  Sql fur model manu  runat  server                       ConnectionString   lt    ConnectionStrings conStr   gt                        SelectCommand  SELECT DISTINCT  manufacturer  FROM                        furniture manufacturer   gt                   lt  asp SqlDataSource gt               lt  td gt           lt  tr gt           lt tr gt               lt td gt                   lt asp Label ID  lbtype  runat  server  Text  Furniture Type                              gt  lt  asp Label gt               lt  td gt               lt td gt                   lt asp DropDownList ID  ddtype  runat  server  AutoPostBack  True  gt                      lt  asp DropDownList gt               lt  td gt           lt  tr gt      lt  table gt    Code Behind     protected void ddmanu SelectedIndexChanged object sender  EventArgs e        string query    select furniture from furniture model where manufacturer           ddmanu SelectedValue ToString              con Open        cmd   new SqlCommand query  con       DataTable dt   Select query       cmd ExecuteNonQuery        ddtype DataSource   dt      ddtype DataTextField    manufacturer       ddtype DataValueField    furniture       ddtype DataBind

User · Answer

You should add AutoPostBack  true  to DropDownList1                   lt asp DropDownList ID  ddmanu  runat  server  AutoPostBack  true                      DataSourceID  Sql fur model manu                          DataTextField  manufacturer  DataValueField  manufacturer                       onselectedindexchanged  ddmanu SelectedIndexChanged  gt                   lt  asp DropDownList gt

User · Answer

I think this is the culprit   cmd   new SqlCommand query  con    DataTable dt   Select query    cmd ExecuteNonQuery     ddtype DataSource   dt    I don t know what that code is supposed to do  but it looks like you want to create an SqlDataReader for that  as explained here and all over the web if you search for  SqlCommand DropDownList DataSource    cmd   new SqlCommand query  con   ddtype DataSource   cmd ExecuteReader      Or you can create a DataTable as explained here   cmd   new SqlCommand query  con    SqlDataAdapter listQueryAdapter   new SqlDataAdapter cmd   DataTable listTable   new DataTable    listQueryAdapter Fill listTable    ddtype DataSource   listTable

User · Answer

The most basic way you can do this in SelectedIndexChanged events of DropDownLists  Check this code         lt asp DropDownList ID  DropDownList1  runat  server  onselectedindexchanged  DropDownList1 SelectedIndexChanged  Width  224px          AutoPostBack  True  AppendDataBoundItems  true  gt       lt asp DropDownList ID  DropDownList2  runat  server          onselectedindexchanged  DropDownList2 SelectedIndexChanged  gt       lt  asp DropDownList gt     protected void DropDownList1 SelectedIndexChanged object sender  EventArgs e          Load DropDownList2    protected void DropDownList2 SelectedIndexChanged object sender  EventArgs e          Load DropDownList3

[c#] How to use the DropDownList's SelectedIndexChanged event

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