simulate an elastic animation with UIPangestureRecognizer
animation, ios, objective-c
Solution
I actually found a really simple solution to this. Not sure why you'd need a third-party library here, and in general I tend to avoid incorporating them if I don't need to.
Your friend here is the hyperbolic tangent (tanh) function. It crosses the x axis at 45 degrees and then hits an asymptote at 1 just after the input value of 2.
I used this to implement horizontal swiping to reveal date/time (similar to how it's done in iOS7 Messages). Use this code in `handlePan:`
frameOffset = -OFFSET_MAX * tanh(translation.x / INPUT_SENSITIVITY);
Play with the OFFSET_MAX and INPUT_SENSITIVITY to tune it for your purposes. I use 80.0f for OFFSET_MAX (maximum distance I want the swipe to move the view) and 150.0f for INPUT_SENSITIVITY.
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As for the end-pan animation, you can use the options field of `UIView animateWithDuration` to set the right animation curve. For the duration, you can either use a fixed duration (e.g., 0.15 seconds) or scale that value based on the total offset pre-return. Given that people expect a faster "snap back" for a larger offset, I've found that using a fixed duration will look pretty good generally.
Problem
I'm trying to use `UIPangestureRecognizer` for simulate an "elastic" effect. I would like drag an UIView around but it should appears anchored in a specific point of his superview. I tried with this code, decreasing the offeset with a multiplier, but it is linear and the effect is not what i'm looking for. ``` float percentage = distance / maxDistance; float multiplier = (1 - percentage) ; CGPoint center = { self.targetView.center.x , self.targetView.center.y + translation.y * multiplier}; [self.targetView setCenter:center]; [recognizer setTranslation:CGPointZero inView:self.view]; ``` I found this repository https://github.com/warrenm/AHEasing, but i don't understand how can i use the `ExponentialEaseOut`.