Changing height of UIView in response to finger drag

This should be straight-forward with a UIPanGestureRecognizer and a little math. To change the view to the correct frame (I'm using the name _viewToChange, so replace that with your view later), simply add:

UIPanGestureRecognizer * pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)];
pan.maximumNumberOfTouches = pan.minimumNumberOfTouches = 1;
[self addGestureRecognizer:pan];

to your init method for the super view, and define the method:

- (void)pan:(UIPanGestureRecognizer *)aPan; {
  CGPoint currentPoint = [aPan locationInView:self];

  [UIView animateWithDuration:0.01f
                   animations:^{
                     CGRect oldFrame = _viewToChange.frame;
                     _viewToChange.frame = CGRectMake(oldFrame.origin.x, currentPoint.y, oldFrame.size.width, ([UIScreen mainScreen].bounds.size.height - currentPoint.y));
                   }];
}

This should animate the view up as the users finger moves. Hope that Helps!

This is my swift solution in doing it using autolayout and a height constraint on the view you want to resize, while setting a top and bottom limit based on the safe areas

private var startPosition: CGPoint!
private var originalHeight: CGFloat = 0

override func viewDidLoad() {
    super.viewDidLoad()

    let panGesture = UIPanGestureRecognizer(target: self, action: #selector(viewDidDrag(_:)))
    resizableView.addGestureRecognizer(panGesture)
}

@objc private func viewDidDrag(_ sender: UIPanGestureRecognizer) {
    if sender.state == .began  {
        startPosition = sender.location(in: self.view)
        originalHeight = detailsContainerViewHeight.constant
    }

    if sender.state == .changed {
        let endPosition = sender.location(in: self.view)
        let difference = endPosition.y - startPosition.y
        var newHeight = originalHeight - difference

        if view.bounds.height - newHeight < topSafeArea + backButtonSafeArea {
            newHeight = view.bounds.height - topSafeArea - backButtonSafeArea
        } else if newHeight < routeDetailsHeaderView.bounds.height + bottomSafeArea {
            newHeight = routeDetailsHeaderView.bounds.height
        }

        resizableView.constant = newHeight
    }

    if sender.state == .ended || sender.state == .cancelled {
        //Do Something if interested when dragging ended.
    }
}

Swift version using UIPanGestureRecognizer

Using PanGesture added to UIView from Storyboard and delegate set to self. UIView is attached to bottom of the screen.

class ViewController: UIViewController {
var translation: CGPoint!
var startPosition: CGPoint! //Start position for the gesture transition
var originalHeight: CGFloat = 0 // Initial Height for the UIView
var difference: CGFloat!

override func viewDidLoad() {
    super.viewDidLoad()
    originalHeight = dragView.frame.height
}

@IBOutlet weak var dragView: UIView! // UIView with UIPanGestureRecognizer

@IBOutlet var gestureRecognizer: UIPanGestureRecognizer!

@IBAction func viewDidDragged(_ sender: UIPanGestureRecognizer) {

    if sender.state == .began {
        startPosition = gestureRecognizer.location(in: dragView) // the postion at which PanGestue Started
    }

    if sender.state == .began || sender.state == .changed {
        translation = sender.translation(in: self.view)
        sender.setTranslation(CGPoint(x: 0.0, y: 0.0), in: self.view)
        let endPosition = sender.location(in: dragView) // the posiion at which PanGesture Ended
        difference = endPosition.y - startPosition.y
        var newFrame = dragView.frame
        newFrame.origin.x = dragView.frame.origin.x
        newFrame.origin.y = dragView.frame.origin.y + difference //Gesture Moving Upward will produce a negative value for difference
        newFrame.size.width = dragView.frame.size.width
        newFrame.size.height = dragView.frame.size.height - difference //Gesture Moving Upward will produce a negative value for difference
        dragView.frame = newFrame
    }

    if sender.state == .ended || sender.state == .cancelled {
        //Do Something
    }
  }
}