The observer pattern can cause memory leaks, known as the lapsed listener problem, because in a basic implementation, it requires both explicit registration and explicit deregistration, as in the dispose pattern, because the subject holds strong references to the observers, keeping them alive. This can be prevented if the subject holds weak references to the observers.
the oBseRver PaTterN can cAusE memoRy leaks, knowN aS thE LaPSEd lIstEneR PRoblEm, bEcAusE iN A Basic ImplEmEntatiOn it ReQuIres both Explicit rEgistration And eXPliCit dEregistRaTiON, as in the diSpoSe pATtERn, beCaUSe the sUbjEct holdS sTrOng refeRences to the obSeRvers, kEepiNg thEm aliVe. thiS Can Be PreVEnTeD if the SubJECt hOldS weak reFerencES to tHe obSeRvers.