Do not call the Activate method. It is called automatically when the property is selected. As implemented in TPropertyEditor, Activate does nothing. Override this method to determine attributes of the property dynamically when the property editor is displayed in the Object Inspector. 

Before Activate is called, the GetAttributes method does not need to provide accurate information about any attributes other than paSubProperties, paVCL, and paMultiSelect. Any other attributes can be computed in an override of the Activate method and stored so that subsequent calls to GetAttributes can provide accurate information. 

GetAttributes 

Initialize