I am not sure how and why you add a control (the tooltip) to the controls collection, but I would advise against this. This is a databound event and it is a bit too late in the page lifecycle to add controls. Besides, after a few ajaxified pagings of the grid you would end up with several tooltips for the same cell, which may result in an unexpected behavior and would weigh down the markup.
What I would suggest is that you use the RadToolTipManager instead, add the cell to its target controls collection and use it to display the value. For more information on this approach please examine the following online demo: http://demos.telerik.com/aspnet-ajax/tooltip/examples/targetcontrolsandajax/defaultcs.aspx?product=grid
. For the difference between the RadToolTip and the RadToolTipManager please examine this one: http://demos.telerik.com/aspnet-ajax/tooltip/examples/tooltipversustooltipmanager/defaultcs.aspx
For your convenience I created and attached a simple page that illustrates the approach. You can find a video with the expected behavior in the following link: http://screencast.com/t/4Zmyx0RWay
. Please note how the cells have different content, yet their IDs remain the same.
All the best,
the Telerik team
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