leak by timer in cell

ex:
should use :
[NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(onNext:) object:nil];
[self performSelector:@selector(onNext:) withObject:nil afterDelay:2];
for:
_nst_Timer = [NSTimer scheduledTimerWithTimeInterval: 2 target:self selector:@selector(onNext:) userInfo:nil repeats:YES];