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class TSpinButton:
...
procedure CMEnabledChanged(var Message: TMessage); message CM_ENABLEDCHANGED;
...
procedure TSpinButton.CMEnabledChanged;
begin
 inherited;
 FUpButton.enabled:=enabled;
 FDownButton.enabled:=enabled;
end;

class TSpinEdit:
...
procedure CMEnabledChanged(var Message: TMessage); message CM_ENABLEDCHANGED;
...
procedure TSpinEdit.CMEnabledChanged;
begin
 inherited;
 FButton.Enabled:=Enabled;
end;