public CustomPanAnimation(UIView view)
{
superViewWidth = view.Superview.Frame.Width;
xOffset = superViewWidth - view.Frame.Width;
var recognizer = new UIPanGestureRecognizer((UIPanGestureRecognizer obj) =>
{
switch (obj.State)
{
case UIGestureRecognizerState.Began:
animator = new UIViewPropertyAnimator(1, UIViewAnimationCurve.EaseOut, () =>
{
var velocity = obj.VelocityInView(view);
if (velocity.X < 0)
{
direction = -1;
}
else
{
direction = 1;
}
var frame = view.Frame;
frame.Offset(direction * xOffset, 0);
view.Frame = frame;
});
animator.PauseAnimation();
progressWhenInterrupted = animator.FractionComplete;
break;
case UIGestureRecognizerState.Changed:
var translation = obj.TranslationInView(view);
animator.FractionComplete = (direction * translation.X / xOffset) + progressWhenInterrupted;
break;
case UIGestureRecognizerState.Ended:
if (Math.Abs(animator.FractionComplete) < 0.3)
{
animator.Reversed = true;
}
var timing = new UICubicTimingParameters(UIViewAnimationCurve.EaseOut);
animator.ContinueAnimation(timing, 0);
break;
}
});
view.UserInteractionEnabled = true;
view.AddGestureRecognizer(recognizer);
}
void Panned(object r)
{
var recognizer = r as UIPanGestureRecognizer;
switch (recognizer.State)
{
case UIGestureRecognizerState.Began:
StartAnimationIfNeeded();
animator.PauseAnimation();
animationProgress = animator.FractionComplete;
break;
case UIGestureRecognizerState.Changed:
var fraction = -recognizer.TranslationInView(momentumView).Y / closedTransform.y0;
if (isOpen)
{
fraction *= -1;
}
if (animator.Reversed)
{
fraction *= -1;
}
animator.FractionComplete = fraction + animationProgress;
break;
case UIGestureRecognizerState.Ended:
case UIGestureRecognizerState.Cancelled:
var yVelocity = recognizer.VelocityInView(momentumView).Y;
var shouldClose = yVelocity > 0; // todo: should use projection instead
if (yVelocity == 0)
{
animator.ContinueAnimation(parameters: null, durationFactor: 0);
break;
}
if (isOpen)
{
if (!shouldClose && !animator.Reversed)
{
animator.Reversed = !animator.Reversed;
}
if (shouldClose && animator.Reversed)
{
animator.Reversed = !animator.Reversed;
}
}
else
{
if (shouldClose && !animator.Reversed)
{
animator.Reversed = !animator.Reversed;
}
if (!shouldClose && animator.Reversed)
{
animator.Reversed = !animator.Reversed;
}
}
var fractionRemaining = 1 - animator.FractionComplete;
var distanceRemaining = fractionRemaining * closedTransform.y0;
if (distanceRemaining == 0)
{
animator.ContinueAnimation(null, 0);
break;
}
var relativeVelocity = NMath.Min(NMath.Abs(yVelocity) / distanceRemaining, 30);
var timingParameters = UISpringTiming.MakeTimingParameters(damping: 0.8f, response: 0.3f, initialVelocity: new CGVector(dx: relativeVelocity, dy: relativeVelocity));
var preferredDuration = new UIViewPropertyAnimator(duration: 0, parameters: timingParameters).Duration;
var durationFactor = preferredDuration / animator.Duration;
animator.ContinueAnimation(parameters: timingParameters, durationFactor: (nfloat)durationFactor);
break;
default:
break;
}
}