Best Practice for Keeping Selected ListBox Item Visible After Postback?

[Robert]

I've implemented a RadListBox which will almost always have more items than will stack vertically, thus there's almost always a scrollbar.  For reasons I've explained in other threads, my application requires that a single-click and a double-click cause a server-side postback.  That part of the equation has long been built and is working fine.

Where I've run into a problem is the age-old issue of selecting a ListBox item near the bottom, having the postback occur, and then the ListBox item no longer in exactly the same vertical position it was before and often not even visible.  I've read several threads in this forum addressing this problem and have come up with this solution of my own:

In the server-side method that handles selecting a listbox item, I added this code:

      Page page = HttpContext.Current.CurrentHandler as Page;<br>      ScriptManager.RegisterStartupScript(page, page.GetType(), Guid.NewGuid().ToString(), "setTimeout(function() {scrollIntoView()}, 100);", true);

Which in turns executes this code on the client after the postback is done:

  function scrollIntoView() {<br>    var slidingZone = $find($('table[id$=_radSlidingZone]')[0].id);<br>    var slidingPane = slidingZone.getPanes()[0];<br>    var listBox = $find($("#" + slidingPane.get_id() + " div[id$=_radListBoxStopes]")[0].id);<br><br>    var item = listBox.get_selectedItem();<br>    if (item != null)<br>      item.scrollIntoView();<br>  }

It seems to be working "okay" but I'm just wondering if, in 2012, this is the best/easiest way to solve this problem or whether there's a simpler/better approach?

Thank you,

Robert

[Dimitar Terziev]

Hello Robert,

I'm glad that you have found a solution on your own, but in general it's hard to entitle a certain solution as the best one. Usually it depends on the specific scenario in which the problem occurs.

In order to help you find another solution to your problem, please open a support ticket and provide a runnable sample with the issue being reproduced so we could debug it locally.

All the best,
Dimitar Terziev
the Telerik team

[Robert]

Dimitar,

I had always thought that you, at Telerik, preferred users of your products, posting queries here as the solutions then tend to help other developers too.

In any case, I would have thought that the issue of keeping a scrolling listbox in place would have been a fundamental one from the start of the creation of the RadListBox.  That's why I posted my question about the Best Practice for effecting this outcome.

Robert

[Robert]

Through further testing I've now discovered that this method I've built is causing a strange JavaScript error that I can't resolve:

    private void EnsureSelectedListBoxItemRemainsVisible()<br>    {<br>      Page page = HttpContext.Current.CurrentHandler as Page;<br>      ScriptManager.RegisterStartupScript(page, page.GetType(), Guid.NewGuid().ToString(), "setTimeout(function() {scrollIntoView()}, 100);", true);<br>    }<br>

  function scrollIntoView() {<br>    var slidingZone = $find($('table[id$=_radSlidingZone]')[0].id);<br>    var slidingPane = slidingZone.getPanes()[0];<br>    var listBox = $find($("#" + slidingPane.get_id() + " div[id$=_radListBoxStopes]")[0].id);<br><br>    var item = listBox.get_selectedItem();<br>    if (item != null)<br>      item.scrollIntoView();<br>  }<br>

Is there another way I can call the "scrollInfoView()" Javascript function for the selected item?

Robert

[Robert]

Please ignore my last post.  I figured out a way to do accomplish it.

What would be great with a future release is if you could get the 'scrolllIntoView' function to precisely keep the listbox in the same position after the postback (to the pixel).  For example, imagine you have a listbox that can display 5 items at one time but there are 10 items in it.  Select the 9th item and cause a postback to occur.  When the listbox is redisplayed, while it's true that the 9th item will still be visible (and selected) it's absolute Y-position will not be identical to what existed before the postback.  It would be much better if it was.

Robert

[Dimitar Terziev]

Hi Rober,

I've forwarded your request to our development team for consideration. As for your problem I'm glad that you have found a solution.

Regards,
Dimitar Terziev
the Telerik team