How can I programatically invalidate the outputcache from a usercontrol

You could add a dependency to the output cached control, and change the dependency to evict the control. Here’s code to do that:

VB.NET

If TypeOf Parent Is System.Web.UI.BasePartialCachingControl Then
            	Cache('dependent') = 'dependent'
            	Dim dep As New CacheDependency(Nothing, New String() {'dependent'}) ’
            	CType(Parent, System.Web.UI.BasePartialCachingControl).Dependency = dep
End If

C#

if (Parent is System.Web.UI.BasePartialCachingControl) 
{ 
	Cache['dependent'] = 'dependent'; 
	CacheDependency dep = new CacheDependency(null, new string[] 'dependent'); 
	((System.Web.UI.BasePartialCachingControl)Parent).Dependency = dep; 
}