Subclass of UITextView that allows placeholder text

PlaceholderTextView

import UIKit

class PlaceholderTextView: UITextView {

    var placeholder: String {
        get {
            return placeholderTextView.text
        }
        set {
            placeholderTextView.text = newValue
            resizePlaceholderFrame()
        }
    }

    var placeholderTextColor: UIColor {
        get {
            return placeholderTextView.textColor
        }
        set {
            placeholderTextView.textColor = newValue
        }
    }

    private let placeholderKey = "placeholder"
    private let fontKey = "font"
    private let attributedTextKey = "attributedText"
    private let textKey = "text"
    private let exclusionPathsKey = "exclusionPaths"
    private let lineFragmentPaddingKey = "lineFragmentPadding"
    private let textContainerInsetKey = "textContainerInset"
    private let textAlignmentKey = "textAlignment"
    private let editableKey = "editable"

    private lazy var placeholderTextView = UITextView()
    private var isPlaceholderPrepared = false

    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        preparePlaceholder()
    }

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

    deinit {

        NSNotificationCenter.defaultCenter().removeObserver(self)
        removeObserver(self, forKeyPath: placeholderKey)
        removeObserver(self, forKeyPath: fontKey)
        removeObserver(self, forKeyPath: attributedTextKey)
        removeObserver(self, forKeyPath: textKey)
        removeObserver(self, forKeyPath: textAlignmentKey)
        removeObserver(self, forKeyPath: editableKey)

        textContainer.removeObserver(self, forKeyPath: exclusionPathsKey)
        textContainer.removeObserver(self, forKeyPath: lineFragmentPaddingKey)

        removeObserver(self, forKeyPath: textContainerInsetKey)
        
    }

    private func preparePlaceholder() {

        assert(!isPlaceholderPrepared, "placeholder has been prepared already: \(placeholderTextView)")
        isPlaceholderPrepared = true

        // the label which displays the placeholder
        // needs to inherit some properties from its parent text view

        placeholderTextView.frame = bounds
        placeholderTextView.opaque = false
        placeholderTextView.backgroundColor = UIColor.clearColor()
        placeholderTextView.textColor = UIColor(white: 0.7, alpha: 0.7)
        placeholderTextView.textAlignment = textAlignment
        placeholderTextView.editable = false
        placeholderTextView.scrollEnabled = false
        placeholderTextView.userInteractionEnabled = false
        placeholderTextView.font = font
        placeholderTextView.isAccessibilityElement = false
        placeholderTextView.contentOffset = contentOffset
        placeholderTextView.contentInset = contentInset
        placeholderTextView.selectable = false
        placeholderTextView.textContainer.exclusionPaths = textContainer.exclusionPaths
        placeholderTextView.textContainer.lineFragmentPadding = textContainer.lineFragmentPadding
        placeholderTextView.textContainerInset = textContainerInset
        placeholderTextView.text = placeholder
        placeholderTextView.hidden = !editable // hide the placeholder when the text view is not editable

        setPlaceholderVisibleForText(text)
        clipsToBounds = true


        // add observers

        NSNotificationCenter.defaultCenter().addObserver(self, selector: "textDidChange:", name: UITextViewTextDidChangeNotification, object: self)

        addObserver(self, forKeyPath: placeholderKey, options: NSKeyValueObservingOptions.New, context: nil)
        addObserver(self, forKeyPath: fontKey, options: NSKeyValueObservingOptions.New, context: nil)
        addObserver(self, forKeyPath: attributedTextKey, options: NSKeyValueObservingOptions.New, context: nil)
        addObserver(self, forKeyPath: textKey, options: NSKeyValueObservingOptions.New, context: nil)
        addObserver(self, forKeyPath: textAlignmentKey, options: NSKeyValueObservingOptions.New, context: nil)
        addObserver(self, forKeyPath: editableKey, options: NSKeyValueObservingOptions.New, context: nil)

        textContainer.addObserver(self, forKeyPath: exclusionPathsKey, options: NSKeyValueObservingOptions.New, context: nil)
        textContainer.addObserver(self, forKeyPath: lineFragmentPaddingKey, options: NSKeyValueObservingOptions.New, context: nil)

        addObserver(self, forKeyPath: textContainerInsetKey, options: NSKeyValueObservingOptions.New, context: nil)

    }

    private func resizePlaceholderFrame() {
        placeholderTextView.frame.size = bounds.size
    }

    private func setPlaceholderVisibleForText(text: String) {
        if text.isEmpty {
            addSubview(placeholderTextView)
            sendSubviewToBack(placeholderTextView)
        } else {
            placeholderTextView.removeFromSuperview()
        }
    }

    // MARK: - Observers

    func textDidChange(notification: NSNotification) {
        setPlaceholderVisibleForText(self.text)
    }

    override func observeValueForKeyPath(keyPath: String, ofObject object: AnyObject, change: [NSObject : AnyObject], context: UnsafeMutablePointer<Void>) {

        switch keyPath {
        case placeholderKey:
            placeholderTextView.text = change[NSKeyValueChangeNewKey] as! NSString as String
        case fontKey:
            placeholderTextView.font = change[NSKeyValueChangeNewKey] as! UIFont
        case attributedTextKey:
            if let newAttributedText = change[NSKeyValueChangeNewKey] as? NSAttributedString {
                setPlaceholderVisibleForText(newAttributedText.string)
            } else {
                setPlaceholderVisibleForText("")
            }
        case textKey:
            let newText = change[NSKeyValueChangeNewKey] as! NSString
            setPlaceholderVisibleForText(newText as! String)
        case exclusionPathsKey:
            placeholderTextView.textContainer.exclusionPaths = change[NSKeyValueChangeNewKey] as? [AnyObject]
            resizePlaceholderFrame()
        case lineFragmentPaddingKey:
            placeholderTextView.textContainer.lineFragmentPadding = change[NSKeyValueChangeNewKey] as! CGFloat
            resizePlaceholderFrame()
        case textContainerInsetKey:
            let value = change[NSKeyValueChangeNewKey] as! NSValue
            placeholderTextView.textContainerInset = value.UIEdgeInsetsValue()
        case textAlignmentKey:
            let alignment = change[NSKeyValueChangeNewKey] as! NSNumber
            placeholderTextView.textAlignment = NSTextAlignment(rawValue: alignment.integerValue)!
        case editableKey:
            let editable = change[NSKeyValueChangeNewKey] as! Bool
            placeholderTextView.hidden = !editable
        default:
            super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
        }
        
    }

    // MARK: - Overrides

    override func layoutSubviews() {
        super.layoutSubviews()
        resizePlaceholderFrame()
    }

    override func becomeFirstResponder() -> Bool {
        setPlaceholderVisibleForText(self.text)
        return super.becomeFirstResponder()
    }

}