ios - Locking UIPanGestureRecognizer to a certain direction -

i have uipangesturerecognizer , i'm trying swipe in 1 direction (up). haven't been able find solution works. thanks. current code:

- (void)pangesture:(uipangesturerecognizer *)recognizer{  cgpoint t = [recognizer translationinview:self.view]; recognizer.view.center = cgpointmake(recognizer.view.center.x + t.x, recognizer.view.center.y + t.y); [recognizer settranslation:cgpointmake(0, 0) inview:self.view];  } 

- (void)pangesture:(uipangesturerecognizer *)recognizer {     cgpoint t = [recognizer translationinview:self.view];      if (t.y < 0) {         t = cgpointmake(0, t.y);     }     else {         t = cgpointmake(0, 0); // @     }      recognizer.view.center = cgpointmake(recognizer.view.center.x + t.x,                                          recognizer.view.center.y + t.y);      [recognizer settranslation:cgpointmake(0, 0) inview:self.view]; } 

to able drag , down use cgpointmake(0, t.y); instead of if