SetParent is the protected implementation of the Parent property. Override SetParent to execute additional code when the value of the Parent property changes. 

The AParent parameter specifies the new parent of the control. 

If the control already has a parent, SetParent removes the control from that parent's list of controls by calling the parent's RemoveControl method. If AParent is not nil (Delphi) or NULL (C++), SetParent calls its InsertControl method to add the control to its list of controls. 

The TControl destructor calls SetParent(nil (Delphi) or NULL (C++)) to remove the control from its parent's control list before destroying the component. 

Destroy 

InsertControl 

Parent 

RemoveControl