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iosobjective-cuikitphysics-engine

Accelerate a UIView using a UIPushBehavior

I'm trying to accelerate a UIView over a time/distance. So far it seems that UIPushBehavior is continuous, i.e it doesn't stop until it hits an immovable object. Is there a way to accelerate a UIView over time? or a distance?

P.S I'm not great in terms of physics vernacular, so please be kind haha

Solution

  • A couple of thoughts:

    1. If you want to slow down the push over time, so that a single push translates to some finite distance traveled, you have to (a) add a linear resistance (so it slows down); and (b) use UIPushBehaviorModeInstantaneous (so it doesn't keep pushing). To add resistance, you would add a UIDynamicItemBehavior:

      UIDynamicItemBehavior *resistanceBehavior = [[UIDynamicItemBehavior alloc] initWithItems:@[viewToAnimate]];
resistanceBehavior.resistance = 1.0;
[self.animator addBehavior:resistanceBehavior];

      In terms of controlling the distance that each push generates, that's a combination of (a) the magnitude of the pushDirection vector you employ; (b) the resistance you apply to your item in the UIDynamicItemBehavior; (c) the size of item you're moving; and (d) the density you apply to your item in UIDynamicItemBehavior. It's probably best to play around with those variables until you achieve the desired distance for a single push.

    2. If, on the other hand, you want to "accelerate a UIView over time", then rather than a UIPushBehaviorModeInstantaneous, you would apply a UIPushBehaviorModeContinuous. By continuously applying a force, it will continue to accelerate in the pushDirection until that UIPushBehavior is removed from the UIDynamicAnimator.