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UITextViewでplaceholderを実装する(Swift)

UITextFieldにはplaceholderがありますが、UITextViewにはありません。
今回は、UITextViewでもplaceholderを使えるように、新しいクラスを作って見ました。

実装方法

  1. UITextViewを継承した新しいClass(ファイル)を作成
  2. UITextViewにCustomClassとしてPlaceHolderTextViewを指定
  3. ソースコードでplaceholderの文字と文字色を指定

ソースコード

ViewController.swift
import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var textView: PlaceHolderTextView!

    override func viewDidLoad() {
        super.viewDidLoad()

        textView.placeHolder = "文字を入力してください"
        textView.placeHolderColor = UIColor(red: 0.1, green: 0.1, blue: 0.1, alpha: 0.8)

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}
PlaceHolderTextView.swift
import UIKit

public class PlaceHolderTextView: UITextView {

    lazy var placeHolderLabel:UILabel = UILabel()
    var placeHolderColor:UIColor      = UIColor.lightGrayColor()
    var placeHolder:NSString          = ""

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

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

    override public func awakeFromNib() {
        super.awakeFromNib()

        NSNotificationCenter.defaultCenter().addObserver(self, selector: "textChanged:", name: UITextViewTextDidChangeNotification, object: nil)
    }

    override public func drawRect(rect: CGRect) {
        if(self.placeHolder.length > 0) {
            self.placeHolderLabel.frame           = CGRectMake(8,8,self.bounds.size.width - 16,0)
            self.placeHolderLabel.lineBreakMode   = NSLineBreakMode.ByWordWrapping
            self.placeHolderLabel.numberOfLines   = 0
            self.placeHolderLabel.font            = self.font
            self.placeHolderLabel.backgroundColor = UIColor.clearColor()
            self.placeHolderLabel.textColor       = self.placeHolderColor
            self.placeHolderLabel.alpha           = 0
            self.placeHolderLabel.tag             = 1

            self.placeHolderLabel.text = self.placeHolder as String
            self.placeHolderLabel.sizeToFit()
            self.addSubview(placeHolderLabel)
        }

        self.sendSubviewToBack(placeHolderLabel)

        if(self.text.utf16.count == 0 && self.placeHolder.length > 0){
            self.viewWithTag(1)?.alpha = 1
        }

        super.drawRect(rect)
    }

    public func textChanged(notification:NSNotification?) -> (Void) {
        if(self.placeHolder.length == 0){
            return
        }

        if(self.text.utf16.count == 0) {
            self.viewWithTag(1)?.alpha = 1
        }else{
            self.viewWithTag(1)?.alpha = 0
        }
    }

}

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