Scroll is jumping when collapse/expand items in tree

[Dmytro]

Hello everyone,

We are having issues with vertical scroll when collapse/expand items in the TreeListView. Scroll starts to jump if we change style for GridViewCell:

<Style x:Key="CellStyle" TargetType="telerik:GridViewCell">
    <Setter Property="MinHeight" Value="50"/>
</Style>

XAML for TreeListView:

<telerik:RadTreeListView x:Name="radTreeListView2"
            AutoGenerateColumns="False"
            Height="450"
            Width="400"
            BorderBrush="Black"
            BorderThickness="5"
            AutoExpandItems="True"
            ScrollViewer.HorizontalScrollBarVisibility="Visible"
            ScrollViewer.VerticalScrollBarVisibility="Visible">
    <telerik:RadTreeListView.ChildTableDefinitions>
        <telerik:TreeListViewTableDefinition ItemsSource="{Binding Items}" />
    </telerik:RadTreeListView.ChildTableDefinitions>

    <telerik:RadTreeListView.Columns>
        <telerik:GridViewDataColumn Header="Name" DataMemberBinding="{Binding Name}"/>
        <telerik:GridViewDataColumn Header="Count" DataMemberBinding="{Binding Count}"/>
    </telerik:RadTreeListView.Columns>
</telerik:RadTreeListView>

Steps to reproduce:
 1. TreeListView should contain enough items, so scroll showed up
 2. Scroll down to the middle or to the end
 3.Collapse/Expand any item
    AR: Scroll jumps to top (or to the middle)
    ER: Scroll stays on the same place, so we can see collapsed/expanded item

Scroll is jumping even if we just put some content in CellTemplate:

<telerik:RadTreeListView.Columns>
    <telerik:GridViewDataColumn Header="Name" DataMemberBinding="{Binding Name}"/>
    <telerik:GridViewDataColumn Header="Count" DataMemberBinding="{Binding Count}">
        <telerik:GridViewDataColumn.CellTemplate>
            <DataTemplate>
                <Border Height="50" Width="200" Background="LightGreen"/>
            </DataTemplate>
        </telerik:GridViewDataColumn.CellTemplate>
    </telerik:GridViewDataColumn>
</telerik:RadTreeListView.Columns>

Please advice.

[Boris]

Hi,

The described behavior occurs because you are changing the GridViewCell Height / MinHeight. This is expected because the TreeListView measures its items by checking their RowHeight. For example when you dynamically change the Height of the GridViewCell the TreeListView doesn't check if the ActualRowHeight for each row has changed (because the TreeListtView would be too slow). When there is no RowHeight specified the TreeListView uses a DefaultRowHeight = 25 to calculate the position of the items in the viewport. In order to return to the default behavior you can set the RowHeight property of the TreeListView. 

I hope this helps.

Regards,
Boris Penev
Telerik

 

 

[Dmytro]

RowHeight is working.

Thanks Boris!

[Jeff]

Hi,
In my case the row height varies based on the cell content... so I cannot pre-determine the RowHeight for the TreeListView control.
How do I ensure the scroll position is correctly calculated?
Thanks!

[Boris]

Hello Jeff,

Unfortunately there aren't any other workaround other than the one mentioned above.

Regards,
Boris
Telerik

 

 

[Dharmavaram]

Hi Boris's

 We too have same issue.Is this problem can't be solved other than this? Every time when we expand one row it is going to top of the RadTreeListView and this behaviour is not good when we have so many rows and again we have to manually scroll till the expanded row.

Regards,

Nagasree

[Dilyan Traykov]

Hi Nagasree,

The only viable solution we can offer is to ensure all of the control's rows have the same height, which can be done via the RowHeight property, as Boris suggested. I'm afraid there is no other feasible approach for handling the scenario where the rows have varying heights.

Regards,
Dilyan Traykov
Progress Telerik