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Error : An -observeValueForKeyPath:ofObject:change:context: message was received but not handled

I want to set height of collection view dynamic according to content, I tried below code :

    override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(true)
    self.ItemCollection.addObserver(self , forKeyPath: "contentSize", options: NSKeyValueObservingOptions.old, context: nil)
func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutableRawPointer) {
    let newHeight : CGFloat = self.ItemCollection.collectionViewLayout.collectionViewContentSize.height
    var frame : CGRect! = self.ItemCollection.frame
    frame.size.height = newHeight
    self.ItemCollection.frame = frame
override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(true)
            self.ItemCollection.removeObserver(self, forKeyPath: "contentSize")
I'm getting error on this line :
 self.ItemCollection.addObserver(self , forKeyPath: "contentSize", options: NSKeyValueObservingOptions.old, context: nil)
Below is the error :
An -observeValueForKeyPath:ofObject:change:context: message was received but not handled.
Key path: contentSize
Observed object: <UICollectionView: 0x102911200; frame = (0 275; 375 360);     clipsToBounds = YES; autoresize = W+TM+H+BM; gestureRecognizers = <NSArray: 0x1c4247a40>; layer = <CALayer: 0x1c02388a0>; contentOffset: {0, 0}; contentSize: {375, 0}; adjustedContentInset: {0, 0, 0, 0}> collection view layout: <UICollectionViewFlowLayout: 0x102543a80>
Change: {
kind = 1;
old = "NSSize: {20, 360}";
Context: 0x0'
                Its an override function, should be override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) for swift 4
– Tj3n
                Nov 7, 2017 at 5:30
        
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