ComboBox.ValueMember Question

ComboBox.ValueMember Question

• BarKey

  That makes sense, thank you Joe. One other quick question, though:
  
  I have a sub that populates my combo box for me. I pass it the combo box to populate, the source (a datatable), the valuemember, as well as the displaymember. It populates just fine, except for two things:
  
  1: I can't set the selected index to -1 to set the initial combo box value to a blank line, due to sorting the datatable, which changes the selectedindex on me.
  2: If I don't have the displaymember and valuemember set in the calling event, it doesn't work properly. Why is that
  
  Code for calling PopulateComboBox:
  

  SGMS.PopulateComboBox(CboServerStatus, myStatusDT, "Status", "StatusID", "cboSort asc")
  
  Code for PopulateComboBox:
  

  Friend Shared Sub PopulateComboBox(ByVal Target As ComboBox, ByVal Source As DataTable, ByVal DisplayMember As String, _

  ByVal ValueMember As String)

  Try

  With Target

  .DataSource = Source

  .DisplayMember = DisplayMember

  .ValueMember = ValueMember

  End With

  Catch ex As Exception

  MessageBox.Show("PopulateComboBox1: " & ex.Message)

  End Try

  End Sub

  
  

• B Sutton

  This is a duplicate of your other post - I've responded to the other post here:
  http://forums.microsoft.com/msdn/ShowPost.aspx PostID=63674
  
  Joe Stegman
  The Windows Forms Team
  Microsoft Corp.

  This posting is provided "AS IS" with no warranties, and confers no rights.

  
  

• LTaylor

  I am able to add a blank row to the dataset, so that works (thanks for the advice on that !)
  
  In regards to my second question, it seems to have been a glitch in my system. Before, I would set the display and value members in the code that bound the data to the combo box, but it wouldn't display properly unless I added the display and value members to the parent function (hopefully I'm using that term correctly :S). That has since cleared itself up (or I fixed whatever was causing it not to display correctly in the first place. :P)
  
  Thank you very much for your replies.

  
  

• Nada Ali

  1: I can't set the selected index to -1 to set the initial combo box value to a blank line, due to sorting the datatable, which changes the selectedindex on me.
  
  The recommended way to handle this is to add a "blank" item to your DataTable.  If you can't do that, then the following should work:
  
  

  With Target .DisplayMember = DisplayMember .ValueMember = ValueMember .DataSource = Source .SelectedIndex = -1 End With

  
  
  2: If I don't have the displaymember and valuemember set in the calling event, it doesn't work properly. Why is that
  
  If you don't set DisplayMember, then the ComboBox won't know to use the "Status" column for the ComboBox text (it would call ToString() on the items which will return "DataRowView").  What do you expect to happen if you don't set DisplayMember
  
  Joe Stegman
  The Windows Forms Team
  Microsoft Corp.

  This posting is provided "AS IS" with no warranties, and confers no rights.
  

  
  

• Prajakta

  Yes - SelectedValue represents the evaluation of the "ValueMember" property on the current item.  If your ComboBox is filled with Customer objects and "ValueMember" is "Name" then the SelecteValue will be Customer.Name of the currently selected customer.  If you don't set the ValueMember, then we call "ToString()" on the current item.  In your case, the current item is a DataRowView (essentially an ADO.NET DataRow) and its ToString() returns the Type name (DataRowView).
  
  Joe Stegman
  The Windows Forms Team
  Microsoft Corp.

  This posting is provided "AS IS" with no warranties, and confers no rights.

  
  

• Conversion

  I've implemented a function to insert a blank row into my datatable, however, I'm running into a few issues with it. Namely, it's not adding a blank entry for all the columns. Is there a way to iterate through the columns in my combobox, and based on the datatype of the column, insert the appropriate blank value
  
  Currently I have the following:
  

  Friend Shared Function InsertBlankRow(ByVal Source As DataTable) As DataTable Dim myNewSource As DataTable = Source Dim myBlankRow As DataRow = myNewSource.NewRow Dim i As Integer MessageBox.Show(myNewSource.Columns.Count) For i = 0 To myNewSource.Columns.Count - 1 MessageBox.Show("DataType is: " & myNewSource.Columns(i).ToString) 'If (myNewSource.Columns(i).DataType() = Odbc.OdbcType.DateTime) Then ' MessageBox.Show("Datatype is datetime!") 'End If myBlankRow(i) = "" Next myNewSource.Rows.InsertAt(myBlankRow, 0) Return myNewSource End Function

  
  
  The problem with this is that it will error out if I try and pass it a datatable that has a datetime column in it. How can I account for that (You can see that I've tried to check for this and failed. :S)
  
• ComboBox.ValueMember Question