How to deal with GridViewDataColumn.CellTemplate and virtualization

[Jose Simas]

Hi,

Given the grid below:

<my:RadGridView 

            x:Name="grdData"

            VerticalAlignment="Stretch"

            ItemsSource="{Binding List}"

            ShowGroupPanel="False"

            AutoGenerateColumns="False"

            EditTriggers="None"

            CanUserSelect="False"

            Tag="{Binding ComboBoxList}"

            >

            <my:RadGridView.Columns>

                <my:GridViewDataColumn Header="Variable" TextAlignment="Center">

                    <my:GridViewDataColumn.CellTemplate>

                        <DataTemplate>

                            <ComboBox 

                                ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, 

                                                AncestorType={x:Type my:RadGridView}, AncestorLevel=1}, Path=Tag}"

                                SelectedValuePath="Value"

                                DisplayMemberPath="Name"

                                SelectedValue="{Binding SelectedItem}"

                                />

                        </DataTemplate>

                    </my:GridViewDataColumn.CellTemplate>

                </my:GridViewDataColumn>

            </my:RadGridView.Columns>

        </my:RadGridView>

Which is a grid with a single column which has a custom datatemplate with a combobox in it. Each item in the list has a value assigned (no ComboBox is empty).

When the list is long and the vertical scrollbars are visible, if I drag the scrollbar down, hiding a few items at the top, sometimes the items that were hidden re-appear unselected (DependencyProperty.UnsetValue).

I solved the issue by turning off the Row Virtualization (EnableRowVirtualization="False") but I would like to know if this is a bug or if I am missing a step when using custom datatemplates with virtualization.

I can submit a bug report with a demo of the problem if you prefer.

Thanks,
Jose

[Veselin Vasilev]

Hi Jose Simas,

That could be a bug, so a sample project will help us to confirm it easily.

On the other hand, may I ask, why don't you use the built-in GridViewComboBoxColumn? You can check the online demo here.

Best wishes,
Veselin Vasilev
the Telerik team

[Jose Simas]

Hi,

Has it happens the error is mine. The line SelectedValue="{Binding SelectedItem}" is wrong, it should read SelectedValue="{Binding Value}" and in this case the Grid works fine with virtualization on. I am sorry for the confusion.

The reason I am not using the built-in GridViewComboBoxColumn is because you have to click three times for it to drop down the list of items: One to put the cell in edit mode, two to set the focus to the combobox and third: drop down the values. My requirement is for the dropdown to show its values with one click only so I had to resort to this custom grid column. Is there any way to have this behaviour with the built-in combo box column?

Regards,
Jose

[Yavor Georgiev]

Hi Jose Simas,

 You can very easily achieve your requirement - you need to set the EditTriggers property of RadGridView to CellClick and you need to set the OpenDropDownOnFocus property of the RadComboBox like so:

<telerik:GridViewComboBoxColumn ...>
  <telerik:GridViewComboBoxColumn.EditorStyle>
    <Style TargetType="telerik:RadComboBox">
      <Setter Property="OpenDropDownOnFocus" Value="True" />
    </Style>
  </telerik:GridViewComboBoxColumn.EditorStyle>
...
</telerik:GridViewComboBoxColumn>

Greetings,
Yavor Georgiev
the Telerik team

[Jose Simas]

Hi,

That is great thanks, it works just fine.

Jose

[Jose Simas]

Hi,

Spoken a bit too soon :-)

It does work but I had to go back to my previous solution because the grid cell does not give any hint that that column is a combobox until you select it. The datatemplate solution shows the traditional combobox triangle that gives the clue to its existence. Since this is the only editable column in the grid then I need to show the clue that that column is selectable. Is this possible with the  GridViewComboBoxColumn? 

Thanks,
Jose

[Yavor Georgiev]

Hello Jose Simas,

 In this case, you can either keep to your current solution, or use a custom CellTemplate (not CellEditTemplate) to display a TextBlock with a small graphical hint. By default, when not in edit mode, the ComboBoxColumn displays its value in a TextBlock - the ComboBox is shown when entering edit mode.

Regards,
Yavor Georgiev
the Telerik team

[Jose Simas]

Hi,

Good idea, I will do that. Many thanks for your timely answers and guidance!

Jose