Problem with scrolling

[Dmitry]

I followed your Example solution (pretty simple stuff) and added a DataBoundListbox to my project. Each item has an ItemTemplate and everything at first displays just fine.

Unfortunately when i start to scroll the box after a few items (sometimes 10 sometimes 7, etc.... seems to vary) my scrolling feels like it hits the end and starts to bounce up. If i play around with it, i can make it scroll down some more, but its very painful.

Any ideas?

My item data template looks like this:

 <DataTemplate x:Key="MyItemTemplate">
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="*" />
                <RowDefinition Height="auto" />
            </Grid.RowDefinitions>
            <Button Grid.Row="0" Grid.RowSpan="2" 
                    Margin="0" BorderBrush="Transparent" 
                    HorizontalAlignment="Stretch"
                    BorderThickness="0" Padding="0">
                <Image Stretch="Fill" Width="425" Height="300"
                    Source="{Binding Path=ItemImage}" />
            </Button>
            <Border Background="Black" Grid.Row="1" Opacity=".75" 
                    HorizontalAlignment="Stretch"
                    Margin="12 0 12 45" IsHitTestVisible="False">
                <TextBlock 
                        Text="{Binding Path=Title}" Margin="12 3 8 3" 
                        IsHitTestVisible="False"
                        Foreground="White" TextWrapping="Wrap" />
            </Border>
        </Grid>
    </DataTemplate>

[Deyan]

Hi Dmitry,

Thanks for contacting us.

We would like to kindly ask you to prepare a sample Windows Phone 7 project that we can use to reproduce the case since the issue that you describe is not known to us. In this way we will be able to directly see what goes wrong and provide you with help.

Please note that you will have to open a new support ticket in order to be able to attach your project.

Thanks for your time.

Kind regards,
Deyan
the Telerik team

[Dmitry]

I will try to get you guys a sample - it will be hard though in the coming weeks as im very busy :(.

[Deyan]

Hello Dmitry,

Thanks for writing back.

I would like to inform you that we have made an attempt to reproduce the behavior that you describe by using the XAML that you sent in your first post but could not reproduce any undesired effects. Therefore a sample project prepared by you would be the way to go and we will be thankful if you manage to provide us with such since we are willing to investigate the case.

Thanks for your understanding and for the time taken.

Greetings,
Deyan
the Telerik team

[Deyan]

Hi Dmitry,

This is a quick follow up with some further details on the issue that you reported.

We have been able to reproduce it with the Q1 2011 version of RadControls for Windows Phone 7. We have also performed some tests with the latest internal build  we have released containing the crucial fixes we have introduced in the controls after the official release. With this version we could not reproduce the issue and therefore I would kindly like to ask you to try reproducing it on your side by using the latest internal build which should be available for you to download from our website in the Downloads section of your account.

Thanks for your time.

We look forward to receiving further feedback on the case.

Best wishes,
Deyan
the Telerik team

[Dmitry]

Deyan,

Did this fix make it into the most recent trial downloads? I want to try your control suite again but want to make sure the public build i will download no longer has this issue.

Thanks,

Dmitry.

[Deyan]

Hi Dmitry,

Thanks for writing back.

Please check out our latest official release and let us know if you still experience this issue.

Regards,
Deyan
the Telerik team

[Tyler]

I'm currently seeing this issue in the latest internal build (05/09/2012).

I have a databound list box that is bound to an observable collection. I have a list picker that the user can change and the data list is updated based on the newly selected item. To refresh the databound list box items I clear the observable collection and then add the new items one by one to the observable collection. Sometimes (not always) when I return back from the list picker, the first new item shows, and the rest of the list is blank until I start scrolling, then the rest of the items instantly appear in the UI. Then, I hit the bottom of the list which causes the 'squish' effect, but when I let go, I see more items in the list. This keeps happening until I finally hit the real bottom.

I have a video clip of this happening that I can share if needed.

[Tyler]

I have narrowed this down even further and can get it to consistently repro. 

Here is the chain of events that causes the problem:

1. Set DataVirtualizationMode to OnDemandAutomatic
2. Load initial set of items from server
3. User scrolls to bottom of list and requests the remaining data from the server
4. Set DataVirtualizationMode to None (there are no more available items from the server)
5. User changes the type of data he/she wants to see
6. Bind the same UI list to a new observable collection
7. Set DataVirtualizationMode to OnDemandAutomatic
8. Attempt to load a new set of data from the server
9. Observe undesirable scrolling/virtualization behavior

There seems to be an issue switching between DataVirtualization modes

[Deyan]

Hi Dmitry,

Thanks for writing.

We have tried to reproduce the undesired behavior in a separate Windows Phone project by using the steps you provided but we did not succeed in doing so. The list box seems to work as expected on our side when dynamically changing the Virtualization Mode and binding to a new collection.

It will be great if you manage to isolate the glitches in a demo project and send it to us for further inspection. You will have to open a new support ticket to upload your project.

Thanks for your time.

Regards,
Deyan
the Telerik team

[Tyler]

I was also unable to reproduce in a separate solution with similar conditions, however I noticed something interesting last night. My problem completely went away when running in Release instead of Debug. Are there are IF DEF or #define's in your control code that could be causing this?

[Deyan]

Hello Tyler,

We do not have any preprocessor directives that change the logic of our controls depending on the compilator mode. Are you testing on the emulator or on a real device?

All the best,
Deyan
the Telerik team