Swiftでtextarea

xcodeで開発するiOSのUI部品でテキストエリアに対応するものが見当たらなかったので実装してみた

import UIKit

public class UITextArea: UITextView {

    var placeholder: String!
    var placeholderColor: UIColor!
    lazy var placeholderLabel: UILabel = UILabel()
    var tipFontSize: CGFloat = 14

    required public init(coder: NSCoder) {
        super.init(coder: coder)
        self.layer.borderColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.1).CGColor
        self.layer.borderWidth = 0.8
        self.layer.masksToBounds = true
        self.layer.cornerRadius = 8.0
    }
    
    override public func awakeFromNib() {
        super.awakeFromNib()
        if (self.placeholder == nil) {
            self.placeholder = ""
        }
        if (self.placeholderColor == nil) {
            self.placeholderColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.2)
        }
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "textDidChanged:", name: UITextViewTextDidChangeNotification, object: nil)
    }
    
    public func textDidChanged(notification: NSNotification!) {
        
        if self.placeholder!.utf16Count == 0 {
            return
        }
        
        if self.text.utf16Count == 0 {
            self.viewWithTag(999)?.alpha = 1.0
        } else {
            self.viewWithTag(999)?.alpha = 0.0
        }
    }
    
    func setText(text: String) {
        super.text = text
        self.textDidChanged(nil)
    }
    
    override public func drawRect(rect: CGRect) {
        if 0 < self.placeholder!.utf16Count {
            self.placeholderLabel.frame = CGRect(x: 8, y: 6, width: self.bounds.size.width - 16, height: 0)
            self.placeholderLabel.text = self.placeholder
            self.placeholderLabel.tag = 999
            self.placeholderLabel.alpha = 0
            self.placeholderLabel.textColor = self.placeholderColor
            self.placeholderLabel.backgroundColor = UIColor.clearColor()
            self.placeholderLabel.font = UIFont.systemFontOfSize(self.tipFontSize)
            self.placeholderLabel.lineBreakMode = NSLineBreakMode.ByWordWrapping
            self.placeholderLabel.numberOfLines = 0
            self.addSubview(self.placeholderLabel)
        }
        self.placeholderLabel.sizeToFit()
        self.sendSubviewToBack(self.placeholderLabel)
        
        if self.text.utf16Count == 0 && 0 < self.placeholder!.utf16Count {
            self.viewWithTag(999)?.alpha = 1.0
        }
        
        super.drawRect(rect)
    }

    deinit {
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }
}