Cascade issues using the drop-down menu in Asp.net

Page files

View code

<Asp: dropdownlist id = "  Dropdownlist1  " Runat = "  Server  " Onselectedindexchanged = "  Dropdownlist1_selectedindexchanged  " Autopostback = "  True  " >

<Asp: listitem> City 1 </ASP: listitem>

<Asp: listitem> City 2 </ASP: listitem>

</ASP: dropdownlist>

<Asp: dropdownlist id = "  Dropdownlist2  " Runat = "  Server  " >

</ASP: dropdownlist>

ProgramFile

View code

Protected   Void Dropdownlist1_selectedindexchanged ( Object Sender, eventargs E)

{

 If (Dropdownlist1.selecteditem. Text = "  City 1  " )

{

Dropdownlist2.items. Clear (); dropdownlist2.items. Add ( "  Area 1  " ); Dropdownlist2.items. Add ( "  Area 2  " );

}

 Else   If (Dropdownlist1.selecteditem. Text = "  City 2  " )

{

Dropdownlist2.items. Clear (); dropdownlist2.items. Add ( "  Area 3 " ); Dropdownlist2.items. Add ( "  Area 4  " );

}

}

Note that the autopostback = "true" of the first dropdownlist must be set. In fact, if such provincial/municipal linkages do not require databases, write them directly in JS, or find many existing ones,
The database is a waste of server resources, and the refreshing effect is not good.

Provides three frameworks (ASPnet, jquery, and extjs) of dropdownlist + Ajax, which are well-linked at the provincial and municipal levels)
Example: http://www.cnblogs.com/downmoon/archive/2010/06/15/1758675.html

 

Add an example of using database data:

Foreground controlsCode:

<Asp: placeholder id = "  Placeholder1 " Runat = "  Server  " >
<Asp: Label id = "  Label1  " Runat = "  Server  " TEXT = "  Module:  " > </ASP: Label>
<Asp: dropdownlist id = " Dropdownlist1  " Runat = "  Server  " 
Onselectedindexchanged = "  Dropdownlist1_selectedindexchanged  "  
Autopostback = "  True  " >
</ASP: dropdownlist>
& Nbsp; <asp: Label id ="  Label2  " Runat = "  Server  " TEXT = "  Category:  " Visible = "  False  " > </ASP: Label>
<Asp: dropdownlist id = "  Dropdownlist2  " Visible = "  False  " Runat = "  Server  " >
</ASP: dropdownlist>
</ASP: placeholder>

Background code segment:

     Protected   String Sqlmodulelist = "" ;
 Protected   String Sqltypelist = "" ;
Sqlhelper = New Sqlhelper ();
 Protected   Void Page_load ( Object Sender, eventargs E)
{
 If (! Ispostback)
{
Modulelist (); //  Drop-down data of the first loaded Module  
 }
}
 Protected   Void Dropdownlist1_selectedindexchanged ( Object Sender, eventargs E)
{
 If (Dropdownlist1.selecteditem. Text! = "" )
{
Sqltypelist = "  Select typeid, typename from ky_sendmessage_type as t, ky_sendmessage_module as m
Where T. moduleid = M. moduleid and T. moduleid =  " + Dropdownlist1.selectedvalue + "" ;
Dataset DS = sqlhelper. readdataset (sqltypelist );
Datatable dt = Ds. Tables [ 0 ];
 If (Dt. Rows. Count! = 0 ) //  Determines whether subcategories exist in the module.  
 {
Label2.visible = True ;
Dropdownlist2.visible = True ;
Dropdownlist2.items. Clear ();
}
 Else 
{
Label2.visible = False ;
Dropdownlist2.visible = False ;
}
Dropdownlist2.datasource = DT;
Dropdownlist2.datavaluefield = "  Typeid  " ;
Dropdownlist2.datatextfield = "  Typename  " ;
Dropdownlist2.databind ();
}
}
 Protected   Void Modulelist ()
{
Sqlmodulelist = "  Select * From ky_sendmessage_module as m  " ;
Dataset DS = sqlhelper. readdataset (sqlmodulelist );
Datatable dt = Ds. Tables [ 0 ];
Dropdownlist1.datasource = DT;
Dropdownlist1.datavaluefield ="  Moduleid  " ;
Dropdownlist1.datatextfield = "  Modulename  " ;
Dropdownlist1.databind ();
}

Part:

Initial loading diagram

Click to load the sub-drop-down list