Swift screen with map and tableView (moving) - swift

Question

I am trying to do something like this in swift. When I use UiTableView, I want my tableView to go up to half a screen and still be scrollable there. After, when I scroll down, it moves back to bottom.
bottom example,
middle example
my code:
#IBOutlet var tableView: UITableView?
#IBOutlet var topOffsetConstraint: NSLayoutConstraint?
var counter: CGFloat = 0.0
var isObserverActive: Bool?
var minOffset: CGFloat?
var maxOffset: CGFloat?
override func viewDidLoad() {
super.viewDidLoad()
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("contentOffset"), name: nil, object: nil)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
override func viewDidAppear(animated: Bool) {
super.viewDidAppear(animated)
self.maxOffset = CGRectGetHeight(self.view.bounds)-44+20
self.minOffset = CGRectGetHeight(self.view.bounds)/2
self.counter = self.minOffset!
self.isObserverActive = true
self.topOffsetConstraint!.constant = self.counter
}
// MARK:
override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
if keyPath == "contentOffset" && self.isObserverActive == true {
self.isObserverActive = false
self.changeHeaderLocation(self.tableView!.contentOffset)
}
}
func changeHeaderLocation(newLocation: CGPoint) {
if self.counter <= self.maxOffset && self.counter >= self.minOffset {
self.counter -= newLocation.y
self.counter = min(max(self.counter, self.minOffset!), self.maxOffset!)
if CLong(self.counter) != CLong(self.minOffset!) && CLong(self.counter) != CLong(self.maxOffset!) {
self.tableView!.contentOffset = CGPointZero
}
}
self.topOffsetConstraint!.constant = self.counter
self.isObserverActive = true
self.view.layoutIfNeeded()
}
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 50
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cellIdentifier: String = "cellID"
let cell: UITableViewCell = tableView.dequeueReusableCellWithIdentifier(cellIdentifier)!
cell.backgroundColor = UIColor.redColor()
cell.textLabel!.text = "\(CLong(indexPath.row))"
return cell
}
How do I do this?