Discuss "Dropdown list" in the .Net Development forum.

Shem · #1 May 27th, 2008, 06:51 AM

Hi Guys

Ok i gotta build my first dropdown list, which in turn will populate another
dropdown list, but lets get the dropdown list right first

I've read that it can be databound? so can i populate the list from a method?
i.e. run the query grab the results in a method of a class and bind my dropdown
list control to this method?

Shem

richyrich · #2 May 27th, 2008, 07:18 AM

It's not something I've done, but I see no reason why you couldn't, you just need to set it as a type that can populate a dropdown.

To populate a dropdownlist in code behind, I'd have something like this:-

Code:

sub build_ddl_myddl()
 
Dim conn as new mysqlconnection(connString)
Dim mycommand as new mysqlcommand("SELECT fld_id,fld_text FROM tbl_name")
mycommand.connection = conn
Dim rs as mysqldatareader
try
      conn.open
      rs = mycommand.executereader
      if rs.hasrows then
         my_ddlid.datasource = rs
         my_ddlid.datavaluefield = "fld_id"
         my_ddlid.datatextfield = "fld_text"
         my_ddlid.databind()
      end if
      rs.close
catch ex as exception
      response.write(ex.message.tostring)
finally
      mycommand.dispose
      conn.close
end try
 
end sub

Like I say, I've not tried it in the way you're trying. I guess you could return the function as a dropdownlist, create the whole thing in your function and then on your page just have:-

Code:

my_ddlid = myBLL.getdropdown

Hope that helps

I suspect J will have a better way of doing it, but in theory what you're trying to do should be no problem. It's just a matter of what you return the data form you function as to manipulate it into a DDL.

jmurrayhead · #3 May 27th, 2008, 07:29 AM

Let's say you wanted to populate your dropdown with a list of users in the system. You already have the users class with the appropriate objects. What you can do is create a new class that is a collection, or List Of the User class:

Code:

Namespace Company.AppName.BO
    Inherits List(Of User)
    
    Public Class UserList
        Public Sub New()
 
        End Sub
    End Class
End Namespace

Notice "List(Of User)". This says, make a list from the class "User".

Now, you can take a function that gets the data to populate this list and return the UserList to bind to the dropdown.

So, in the BLL, you'll have this function: GetUserList() As UserList

In the DAL, the same thing: GetUserList() As UserList

Then just bind it to the DropDown

For example of the list, see here: Building Layered Web Applications with Microsoft ASP.NET 2.0 - Part 1 - Imar.Spaanjaars.Com

Download the sample file and check the "App_Code\BusinessObject\Collections" folder.

richyrich · #4 May 27th, 2008, 12:05 PM

J

How would you then create a dropdown that, for example, used a primary key field as the option value and firstname & " " & surname as the text?

Just to give me some pointers...

Thanks

jmurrayhead · #5 May 27th, 2008, 12:08 PM

Because you're using the object as a datasource, you would then set those values to the equivalent properties of the class. You might want to make an additional property "FullName" that returns the concatenated values of FirstName and Surname and set that as the text.

Wolffy · #6 May 27th, 2008, 01:39 PM

RR;
There are no less than 8 ways to bind a DDL (so I've read). If you are wanting to bind to the results of a query in a data table then:

Code:

Dim sql As String = "SELECT id, firstname || ' ' || surname as fullName from aTable"
Dim da As New SqlDataAdapter(sql, "data source=.;initial catalog=myDB;user id=sa")
 Dim dt As New DataTable
 da.Fill(dt)
 da.Dispose()
 Me.DropDownList1.DataSource = dt
 Me.DropDownList1.DataTextField = "fullName"
 Me.DropDownList1.DataValueField = "id"
 Me.DropDownList1.DataBind()

Note that || is the concat for Oracle, your SQL may differ.

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Discuss "Dropdown list" in the .Net Development forum.

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