The event handler for the System.Web.UI.Control.Unload event, which occurs when the Web Part is being unloaded from memory.
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
If your Web Part needs to perform any final cleanup before closing, such as closing files, closing database connections, and discarding objects, you can subscribe to the System.Web.UI.Control.Unload event by adding an appropriate event handler to the Web Part's constructor. For example:
this.Unload += new EventHandler (MyUnloadHandler);