UITextView Placeholder support

UITextView+Placeholder.swift

import UIKit

// https://stackoverflow.com/a/50671026
extension UITextView {
    private class PlaceholderLabel: UILabel { }

    private var placeholderLabel: PlaceholderLabel {
        guard let label = subviews.first(where: { $0 is PlaceholderLabel }) as? PlaceholderLabel else {
            let label = PlaceholderLabel(frame: .zero)
            label.font = font
            label.textColor = .placeholderText
            addSubview(label)
            return label
        }
        return label
    }

    @IBInspectable
    var placeholder: String {
        get {
            return placeholderLabel.text ?? ""
        }
        set {
            let placeholderLabel = self.placeholderLabel
            placeholderLabel.text = newValue
            placeholderLabel.numberOfLines = 0
            let width = frame.width - textContainer.lineFragmentPadding * 2
            let size = placeholderLabel.sizeThatFits(CGSize(width: width, height: .greatestFiniteMagnitude))
            placeholderLabel.frame.size.height = size.height
            placeholderLabel.frame.size.width = width
            placeholderLabel.frame.origin = CGPoint(x: textContainer.lineFragmentPadding + textContainerInset.left, y: textContainerInset.top)

            textStorage.delegate = self
        }
    }
}

extension UITextView: NSTextStorageDelegate {
    public func textStorage(_ textStorage: NSTextStorage, didProcessEditing editedMask: NSTextStorage.EditActions, range editedRange: NSRange, changeInLength delta: Int) {
        if editedMask.contains(.editedCharacters) {
            placeholderLabel.isHidden = !text.isEmpty
        }
    }
}