uitextview_vcta_swift

class TextView: UITextView {

    override init(frame: CGRect) {
        super.init(frame: frame)
        addContentSizeObserver()
    }
    
    override init(frame: CGRect, textContainer: NSTextContainer?) {
        super.init(frame: frame, textContainer: textContainer)
    }

    required init(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    private func addContentSizeObserver() {
        self.addObserver(self, forKeyPath: "contentSize", options: NSKeyValueObservingOptions.New, context: nil)
    }
    
    private func removeContentSizeObserver() {
        self.removeObserver(self, forKeyPath: "contentSize")
    }
    
    override func observeValueForKeyPath(keyPath: String, ofObject object: AnyObject, change: [NSObject : AnyObject], context: UnsafeMutablePointer<Void>) {
        var top = (bounds.size.height - contentSize.height * zoomScale) / 2.0
        top = top < 0.0 ? 0.0 : top
        contentOffset = CGPoint(x: contentOffset.x, y: -top)
    }
    
    deinit {
        removeContentSizeObserver()
    }
    
}