Add onselectedindexchanged to the dropdownlist Control item in the gridview to implement cascading

The onselectedindexchanged event can be directly associated with the server. There is no need to associate a button. In the selectedindexchanged event, you can find the drop-down box event through the sender and find the current gridviewrow through the parent twice, find another row drop-down box in findcontrol and bind the data.
<Asp: gridview id = "gridview1" runat = "server" autogeneratecolumns = "false" onrowdatabound = "gridview1_rowdatabound">
<Columns>
<Asp: templatefield>
<Headertemplate>
Serial number
</Headertemplate>
<Itemtemplate>
<Asp: Label id = "lblindex" runat = "server" text = "<% # container. dataitemindex %>"> </ASP: Label>
</Itemtemplate>
</ASP: templatefield>
<Asp: templatefield>
<Headertemplate>
Contract signature
</Headertemplate>
<Itemtemplate>
<Asp: dropdownlist id = "ddlcontractno" runat = "server" autopostback = true onselectedindexchanged = "ddlcontractno_selectedindexchanged">
</ASP: dropdownlist>
</Itemtemplate>
</ASP: templatefield>
<Asp: templatefield>
<Headertemplate>
Item No.
</Headertemplate>
<Itemtemplate>
<Asp: dropdownlist id = "ddlmaterielno" runat = "server">
</ASP: dropdownlist>
</Itemtemplate>
</ASP: templatefield>
</Columns>
</ASP: gridview>

Public partial class _ default: system. Web. UI. Page
{
Protected void page_load (Object sender, eventargs E)
{
If (this. Page. ispostback)
Return;
Binddata ();
}

Protected void binddata ()
{
Arraylist Al = new arraylist ();
For (INT I = 0; I <15; I ++)
{
Al. Add (I );
}
This. gridview1.datasource = Al;
This. gridview1.databind ();
}

/// <Summary>
/// Obtain all contracts
/// </Summary>
/// <Returns> </returns>
Protected list <contract> getallcontract ()
{
List <contract> List = new list <contract> ();
For (INT I = 0; I <5; I ++)
{
Contract Contract = new contract ();
Contract. ID = I + 1;
Contract. Name = "contract" + contract. ID;
Contract. No = "no" + contract. ID;
List. Add (contract );
}
Return list;
}

Protected list <materiel> getallmaterielbycontractno (string contractno)
{
List <materiel> List = new list <materiel> ();
For (INT I = 0; I <10; I ++)
{
Materiel materiel = new materiel ();
Materiel. ID = I + 1;
Materiel. Name = "materiel" + contractno + materiel. ID;
Materiel. No = contractno + materiel. ID;
Materiel. contractno = contractno;
List. Add (materiel );
}
Return list;
}

Protected void gridview1_rowdatabound (Object sender, gridviewroweventargs E)
{
If (E. Row. rowtype! = Datacontrolrowtype. datarow)
Return;
Dropdownlist ddlcontractno = (dropdownlist) E. Row. cells [1]. findcontrol ("ddlcontractno "));
Ddlcontractno. datasource = getallcontract ();
Ddlcontractno. datatextfield = "no ";
Ddlcontractno. databind ();
Ddlcontractno. selectedindex = 0;
Bindmaterieldropdownlist (E. Row, ddlcontractno. selectedvalue );
}

Protected void ddlcontractno_selectedindexchanged (Object sender, eventargs E)
{
Dropdownlist ddlcontractno = (dropdownlist) sender;
Gridviewrow ROW = (gridviewrow) ddlcontractno. Parent. parent;
Bindmaterieldropdownlist (row, ddlcontractno. selectedvalue );
}

Protected void bindmaterieldropdownlist (gridviewrow row, string contractno)
{
Dropdownlist ddlmaterielno = (dropdownlist) Row. cells [2]. findcontrol ("ddlmaterielno ");
Ddlmaterielno. datasource = getallmaterielbycontractno (contractno );
Ddlmaterielno. datatextfield = "no ";
Ddlmaterielno. databind ();
}
}