column not showing data when switching out the cell element to a custom type

Hello, David,   

Let me start with a brief explanation of the options that you have in RadGridView. I would like to pay attention to the difference between using a custom cell element and a custom editor. Adding elements to the grid cells will display these elements in the cells while they are not in edit mode. Hence, you can almost always see the elements. Once the user tries to edit a cell value, this cell enters edit mode and an editor is being activated considering the value stored in the column. The editor is shown only for a single cell at a time and it is closed once the value is committed or rejected.

Note that RadDropDownListElement and RadTextBoxElement host the MS TextBox. Using controls in grid cells  may slow down the scrolling and will cause visual glitches as they do not support clipping. In such cases, a better option would be using custom editors. Thus, you can construct the desired editor and activate it for the respective cell. 

As to the precise case, I have reviewed the provided code snippet. In the custom GridDataCellElement, the CreateChildElements method is the appropriate place to add elements to the cells which you want to display. Please refer to the following help article which demonstrates a sample approach how to construct custom cells. You can use any elements that you need: 

https://docs.telerik.com/devtools/winforms/controls/gridview/cells/creating-custom-cells 

However, if you want only to show the drop down when the cell is being edited, you can use the EditorRequired event and there specify what editor type to be used. You don't need a custom cell for this. If the default editors don't fit your needs, you can always construct a custom one: https://docs.telerik.com/devtools/winforms/controls/gridview/editors/using-custom-editors 

Feel free to use this approach which suits your scenario best. I hope this information helps. If you need any further assistance please don't hesitate to contact me. 

Regards,
Dess | Tech Support Engineer, Sr.
Progress Telerik

Thank you for looking. What element do i need to add in the CreateChildElements method to make this cell appear like the others? Can you provide an example? I only want to display the value that is on the object while the cell is not in edit mode.

Thanks.

Hello, David,   

To be honest, I am still not sure whether you want to display the custom element, e.g. RadDropDownListElement, constantly or only while you are editing a cell. If you want to display the element constantly for all cells, then you need to create a custom cell.

However, if you want to display the element only in edit mode, you don't need to create a custom cell element, but just a custom editor and use a default column. Then, replace the default editor with the custom one in the EditorRequired event: https://docs.telerik.com/devtools/winforms/controls/gridview/editors/using-custom-editors

I have prepared a sample project for your reference. Here is illustrated the achieved result: 

 Private Sub RadGridView1_EditorRequired(sender As Object, e As EditorRequiredEventArgs)
     If Me.RadGridView1.CurrentColumn.Name = "ActionNumber" Then
         Dim editor As New MyEditor() 
         e.Editor = editor
     End If

 End Sub

 Private Sub RadGridView1_CellEditorInitialized(sender As Object, e As GridViewCellEventArgs)
     Dim editor As MyEditor = TryCast(e.ActiveEditor, MyEditor)
     If editor IsNot Nothing Then
         editor.speedDropdown.DataSource = BuildSpecialList(DirectCast(Me.RadGridView1.CurrentRow.DataBoundItem, GenData))
         editor.speedDropdown.DisplayMember = "DisplayValue"
         editor.speedDropdown.ValueMember = "Value" 
     End If 
 End Sub


 Private Function BuildSpecialList(d As GenData) As List(Of GenericItem(Of Double))
     Dim l As New List(Of GenericItem(Of Double))
     Dim g As New GenericItem(Of Double)
     g.DisplayValue = ""
     g.Value = -1
     l.Add(g)
     g = New GenericItem(Of Double)
     g.DisplayValue = d.SpecialNumber1.ToString
     g.Value = d.SpecialNumber1
     l.Add(g)
     g = New GenericItem(Of Double)
     g.DisplayValue = d.SpecialNumber2.ToString
     g.Value = d.SpecialNumber2
     l.Add(g)
     Return l
 End Function

 Public Class MyEditor
 Inherits BaseGridEditor
     Dim stack As StackLayoutElement
     Public speedDropdown As RadDropDownListElement
     Dim spinEditor As RadSpinElement
     Protected Overrides Function CreateEditorElement() As RadElement
         stack = New StackLayoutElement
         stack.StretchHorizontally = True
         speedDropdown = New RadDropDownListElement
         spinEditor = New RadSpinElement
         spinEditor.MaxValue = 1000
         stack.Children.Add(speedDropdown)
         stack.Children.Add(spinEditor)

         AddHandler speedDropdown.SelectedIndexChanged, AddressOf speedDropdown_SelectedIndexChanged
         Return stack
     End Function

     Public Overrides Property Value As Object
         Get
             Return spinEditor.Value
         End Get
         Set(value As Object)
             spinEditor.Value = value
         End Set
     End Property

     Private Sub speedDropdown_SelectedIndexChanged(sender As Object, e As UI.Data.PositionChangedEventArgs)
         Dim speedDropdown As RadDropDownListElement = CType(sender, RadDropDownListElement)
         Dim d As GenData = speedDropdown.Tag
         If d IsNot Nothing Then
             Dim data As GenericItem(Of Double) = speedDropdown.SelectedItem.DataBoundItem
             d.ActionNumber = data.Value
         End If 
     End Sub

 End Class

Note that this is just a sample approach and it may not cover all possible cases. Please give the sample project a try and see how it works for your case. Feel free to modify and extend it in a way which suits your custom requirements best.  

Should you have further questions please let me know.

Regards,
Dess | Tech Support Engineer, Sr.
Progress Telerik