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Scrollbar arrows and virtual scrolling
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Wesley
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Wesley asked on 06 Jun 2008, 05:05 AM
In the demo here:

http://www.telerik.com/DEMOS/ASPNET/Prometheus/Grid/Examples/Client/VirtualScrollPaging/DefaultCS.aspx

if you grab the scrollbar thumb, and move to various pages, the Grid correctly shows the content.

But, if you click the scrollbar arrow down a couple of times, a blank area is exposed at the bottom of the grid.  If you click a few more times, the grid will render the second page.  The same happens if you're on the second page - if you click on the up arrow a few times, you get a blank area at the top of the grid, and then after a few more clicks it fetches the first page.

Is there any way to make this more smooth, so that the user doesn't get the feeling that the rows are being loaded a page at a time, and the blank areas don't appear?

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Konstantin Petkov
Telerik team
answered on 09 Jun 2008, 07:36 AM
Hello Wesley,

Indeed, this is the default behavior of virtual scrolling RadGrid's feature and I'm afraid there is no solution out-of-the-box. You can however chose the custom implementation in the Grid below: Yahoo-style scrolling. It loads the items on demand so that you don't get blank areas while hitting the scrolling arrows.

Regards,
Konstantin Petkov
the Telerik team

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Wesley
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answered on 09 Jun 2008, 04:25 PM
Thank you for your response.  It's good to know that what I'm looking for can't currently be done.

 Unfortunately, I don't like the "Yahoo" / "Google" example that is shown on the example page for the following reasons:

1) When the page first loads, the size of the scroll thumb is such that the user thinks that they are seeing about 80% of the entries.  To be useful, the scroll thumb should always be sized to show the percentage of the entries that are in view.

2) To scroll to the last entry in the grid in the example (with 9 pages of data), you must scroll the scrollbar to the bottom 9 times, which is not very helpful, especially as the number of rows grows.

I'll file a feature request for the features I'm interested in, so that perhaps I can use the grid scrolling in a future version.

Thanks again!
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S
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answered on 28 Jan 2010, 04:36 PM
I absolutely agree with all the points made in this post.  Have any of these issues been addressed in recent versions?  We use the RadComboBox which does a beautiful job of load on demand:

http://demos.telerik.com/aspnet-ajax/combobox/examples/populatingwithdata/autocompletesql/defaultcs.aspx

The virtual scrolling model in the RadGrid seems almost unusable.

For example, just looking at the telerik demo,
http://demos.telerik.com/aspnet-ajax/grid/examples/client/virtualscrollpaging/defaultcs.aspx

If you click in the empty space beneath the scrollbar, you get to see the last two rows (that weren't visible on the first page, but are part of page 1) for just a second or two and then they're gone, replaced by page 2.  So you the user would have to know that the page size is 14, but you can only see 12 and therefore you should use the arrow button to see the last two items.  Not the scrollbar.

Completely unacceptable from a user perspective.

Are their any workarounds?  Or bug reports/feature requests that I could be added as a 'watcher' on?

Thank you.
Sarah










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Dimo
Telerik team
answered on 01 Feb 2010, 02:25 PM
Hello Sarah,

I am afraid that the virtual scrolling behavior is such by design - other vendors provide it the same way. The problem is that this is not scrolling, but paging, so it cannot look exactly like scrolling.

I can suggest you to use virtual scrolling and set the page size to a suitable value so that all items fit in the visible area.

By the way, the RadComboBox scrolling behavior that you have said to be beatiiful (thank you) is actually the Yahoo-like, which is demonstrated in the second RadGrid here:

http://demos.telerik.com/aspnet-ajax/grid/examples/client/virtualscrollpaging/defaultcs.aspx

You can consider using that option instead.

Sincerely yours,
Dimo
the Telerik team

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Konstantin Petkov
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Wesley
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