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Specified element is already the logical child of another element error with my usercontrol in CellEditTemplate.

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Craig
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Craig asked on 24 Oct 2013, 11:12 AM
Hi
I have defined a user control that I display in a CellEditTemplate. I get the error "Specified element is already the logical child of another element... " in the second attempt to edit the cell. It displays my usercontrol successfully on the first edit attempt. My usercontrol is exposed via a viewmodel exposed as a property of my datacontext's viewmodel.

Here's an extract of the XAML.
<telerik:GridViewDataColumn.CellEditTemplate>
    <DataTemplate>
        <DockPanel HorizontalAlignment="Stretch" VerticalAlignment="Top">
            <telerik:RadDropDownButton DockPanel.Dock="Top" HorizontalAlignment="Stretch" Height="22"
                                       Content="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}, Path=DataContext.AcctVm.SelectedAccount.Account_Code,Mode=TwoWay}"
                                       VerticalAlignment="Center" HorizontalContentAlignment="Left">
                <telerik:RadDropDownButton.DropDownContent>
                        <ContentControl Content="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}, Path=DataContext.AcctVm.View}"
                                        VerticalAlignment="Stretch" Height="300" />
                </telerik:RadDropDownButton.DropDownContent>
            </telerik:RadDropDownButton>
        </DockPanel>
    </DataTemplate>
</telerik:GridViewDataColumn.CellEditTemplate>

Is there a problem with this XAML or do you need more information?
Thanks
Craig

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Craig
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answered on 28 Oct 2013, 02:57 PM
I think this is caused by the data bindings. I may also not have implemented all the required 'plumbing' in my user control to facilitate what I want to do, which is this:
  1. Load a grid with items.
  2. Implement a CellEditTemplate that displays my user control (currently I am hosting it in a RadDropDown button) when one of the grid cells is edited.
  3. When an item in my usercontrol is selected, I want the selected value to be used to update the cell value in the grid.
(In essence a look up to a reference table where my user control makes it easy to view the refererence data structure and controls what may be selected).

I'm trying to find a similar example but I haven't had any luck yet.

Are there any samples that may be similar?

Thanks
Craig

 
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Yoan
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answered on 29 Oct 2013, 09:41 AM
Hello Craig, 

I would suggest you to take a look at this and this articles, where you can find more information about this type of problem. I believe you will find them helpful.

Regards,
Yoan
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Craig
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answered on 29 Oct 2013, 10:19 AM
Hi Yoan,
Thanks for your reply. I've now removed the ContentControl and host my view directly in the DropDownContent. The error no longer occurs but I am unable to establish data binding in the scenario I described.
I'm wondering if attached properties would help but I've no experience in using them.
I'm still looking for a sample.
Regards,
Craig 
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Craig
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answered on 30 Oct 2013, 03:25 PM
I think I'm getting closer. I've defined a DependencyProperty on the child view but I'm still having difficulty wiring this up to the grid cell value.

In summary, I've defined a user control that is composed of number of controls that allows a user to select an item. The selected item is exposed as a property of the view model. I want the selected item to be linked to the DependencyProperty and I want the item bound to the cell in the parent view's radgridview to be bound to the selected item.

Is there a general pattern and associated sample somewhere?

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Yoan
Telerik team
answered on 01 Nov 2013, 11:45 AM
Hello Craig,

In order to help you further, I will need some more information. May I ask you to share your implementation? It would be even better if you can send me a demo project which I can check locally. 

Looking forward to hearing from you.

Regards,
Yoan
Telerik
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Craig
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answered on 01 Nov 2013, 02:40 PM
Hi Yoan,
I've opened ticket 754103 with the sample solution attached.
I've simplified it by not using my more complicated user control because I think it may be answered using a RadComboBox.
In the grid view the first two columns are read only. In the third column I'm using a GridViewComboBoxColumn. In this column the grid dept_code value is changed when I select a new value from the list (although I have to click out of the cell for the trigger; not sure why).
The last column demonstrates the issue I have. Because I want to use a more sophisticated selection mechanism I host the usercontrol in a CellEditTemplate (in this example a RadComboBox). The binding I have defined does not seem to link the grid Dept_Code with the selected item Account_Code which is what I need.
I would like to achieve this using binding and I suspect I need to amend my user control in some way to do it but I do not know how.

Thanks
Craig
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Craig
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answered on 03 Nov 2013, 08:38 PM
Hi Yoan,
I reviewed the test project again over the weekend since it did not really replicate what I was currently doing in my project proper.
I'm glad to say I have managed to get it to work as I would like using a dependency property. It was down to my poor understanding of dependency properties and data binding. (I can't believe how much time I've wasted trying to fix this).
I have attached an updated version of the test project to the support ticket should you want to make it available on the forum. I've added another column which displays a simple user control that exposes a dependency property.
Joel Cochran's sample project at PracticalMVVM.com and Colin Eberhardt's article 'A Simple Pattern for Creating Re-usable Usercontrols in WPF / Silverlight' (http://www.scottlogic.com/blog/2012/02/06/a-simple-pattern-for-creating-re-useable-usercontrols-in-wpf-silverlight.html) helped me return to basics and solve the issue. Of course, not forgetting to thank you at Telerik for your patience.
Craig
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Yoan
Telerik team
answered on 04 Nov 2013, 09:33 PM
Hi Craig,

I am glad to hear that you have resolved the problem by yourself.

Please if you face any further difficulties do not hesitate to contact us.

Regards,
Yoan
Telerik
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Learn what features your users use (or don't use) in your application. Know your audience. Target it better. Develop wisely.
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