When the AutoTooltipify feature of the tooltip manager is enabled, it attaches event handlers to all elements with a title attribute as soon as it initializes. This is during the Sys.Application.Init phase (and event).
Using the OnLoad event of the calenar (or any other similar control) cannot guarantee that the tooltip manager has not initialized yet and has not attached those handlers. Thus, RadToolTips attempt to show up when the elements are hovered, but since their title attribute is no longer there, the tooltips are blank.
What I can suggest is the following:
- Use an earlier event to remove title attributes (e.g., the document.ready jQuery event). You can access the datepicker through its class, for example, instead of using the sender reference.
- Use the OnClientBeforeShow event of the tooltips to cancel it when your conditions are met (e.g., the tooltip has no text, a certain condition is met for its target, etc.). This could be a more generic approach but it would require some investigation on your end so you can find the exact conditions and checks in order to achieve the functionality you desire.
As you can see there is no really straightforward way to do this, because AutoTooltipify is a really simple feature. It provides a lot of automation, but this comes at the price of less customization options.
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