它更多的是个性化你的textField，但无论如何，我将分享这段代码从另一个页面，使它更好一点:

import UIKit
extension UITextField {
func setBottomLine(borderColor: UIColor, fontColor: UIColor, placeHolderColor:UIColor, placeHolder: String) {
    self.borderStyle = UITextBorderStyle.none
    self.backgroundColor = UIColor.clear
    let borderLine = UIView()
    let height = 1.0
    borderLine.frame = CGRect(x: 0, y: Double(self.frame.height) - height, width: Double(self.frame.width), height: height)
    self.textColor = fontColor
    borderLine.backgroundColor = borderColor
    self.addSubview(borderLine)
    self.attributedPlaceholder = NSAttributedString(
        string: placeHolder,
        attributes: [NSAttributedStringKey.foregroundColor: placeHolderColor]
    )
  }
}

你可以这样使用它:

self.textField.setBottomLine(borderColor: lineColor, fontColor: fontColor, placeHolderColor: placeHolderColor, placeHolder: placeHolder)

知道你有一个UITextField连接到一个ViewController。

来源:http://codepany.com/blog/swift-3-custom-uitextfield-with-single-line-input/

在Swift 3.0中，使用

let color = UIColor.lightText
textField.attributedPlaceholder = NSAttributedString(string: textField.placeholder, attributes: [NSForegroundColorAttributeName : color])

在Siwft 5.0 +使用

let color = UIColor.lightText
let placeholder = textField.placeholder ?? "" //There should be a placeholder set in storyboard or elsewhere string or pass empty
textField.attributedPlaceholder = NSAttributedString(string: placeholder, attributes: [NSAttributedString.Key.foregroundColor : color])

Xcode 9.2 Swift 4

extension UITextField{
    @IBInspectable var placeHolderColor: UIColor? {
        get {
            return self.placeHolderColor
        }
        set {
            self.attributedPlaceholder = NSAttributedString(string:self.placeholder != nil ? self.placeholder! : "", attributes:[NSAttributedStringKey.foregroundColor: newValue!])
        }
    }
}

在我的例子中，我必须将占位符设置为黑色。UITextField的名字是passwordText。下面的代码是在Swift 5中测试的，对我来说工作得很好。我也有一个现有的文本对应的占位符。

let placeholderColor = UIColor.black
passwordText.attributedPlaceholder = NSAttributedString(string: passwordText.placeholder!, attributes: [NSAttributedString.Key.foregroundColor : placeholderColor])

这里我正在写UITextField的所有UIDesignable。在这段代码的帮助下，你可以直接从storyboard中的UI文件Inspector中访问它

@IBDesignable
class CustomTextField: UITextField {

@IBInspectable var leftImage: UIImage? {
    didSet {
        updateView()
    }
}

@IBInspectable var leftPadding: CGFloat = 0 {
    didSet {
        updateView()
    }
}

@IBInspectable var rightImage: UIImage? {
    didSet {
        updateView()
    }
}

@IBInspectable var rightPadding: CGFloat = 0 {
    didSet {
        updateView()
    }
}

private var _isRightViewVisible: Bool = true
var isRightViewVisible: Bool {
    get {
        return _isRightViewVisible
    }
    set {
        _isRightViewVisible = newValue
        updateView()
    }
}

func updateView() {
    setLeftImage()
    setRightImage()

    // Placeholder text color
    attributedPlaceholder = NSAttributedString(string: placeholder != nil ?  placeholder! : "", attributes:[NSAttributedString.Key.foregroundColor: tintColor])
}

func setLeftImage() {
    leftViewMode = UITextField.ViewMode.always
    var view: UIView

    if let image = leftImage {
        let imageView = UIImageView(frame: CGRect(x: leftPadding, y: 0, width: 20, height: 20))
        imageView.image = image
        // Note: In order for your image to use the tint color, you have to select the image in the Assets.xcassets and change the "Render As" property to "Template Image".
        imageView.tintColor = tintColor

        var width = imageView.frame.width + leftPadding

        if borderStyle == UITextField.BorderStyle.none || borderStyle == UITextField.BorderStyle.line {
            width += 5
        }

        view = UIView(frame: CGRect(x: 0, y: 0, width: width, height: 20))
        view.addSubview(imageView)
    } else {
        view = UIView(frame: CGRect(x: 0, y: 0, width: leftPadding, height: 20))
    }

    leftView = view
}

func setRightImage() {
    rightViewMode = UITextField.ViewMode.always

    var view: UIView

    if let image = rightImage, isRightViewVisible {
        let imageView = UIImageView(frame: CGRect(x: 0, y: 0, width: 20, height: 20))
        imageView.image = image
        // Note: In order for your image to use the tint color, you have to select the image in the Assets.xcassets and change the "Render As" property to "Template Image".
        imageView.tintColor = tintColor

        var width = imageView.frame.width + rightPadding

        if borderStyle == UITextField.BorderStyle.none || borderStyle == UITextField.BorderStyle.line {
            width += 5
        }

        view = UIView(frame: CGRect(x: 0, y: 0, width: width, height: 20))
        view.addSubview(imageView)

    } else {
        view = UIView(frame: CGRect(x: 0, y: 0, width: rightPadding, height: 20))
    }

    rightView = view
}


@IBInspectable public var borderColor: UIColor = UIColor.clear {
    didSet {
        layer.borderColor = borderColor.cgColor
    }
}

@IBInspectable public var borderWidth: CGFloat = 0 {
    didSet {
        layer.borderWidth = borderWidth
    }
}

@IBInspectable public var cornerRadius: CGFloat = 0 {
    didSet {
        layer.cornerRadius = cornerRadius
    }
}
@IBInspectable public var bottomBorder: CGFloat = 0 {
    didSet {
       borderStyle = .none
        layer.backgroundColor = UIColor.white.cgColor

        layer.masksToBounds = false
     //   layer.shadowColor = UIColor.gray.cgColor
        layer.shadowOffset = CGSize(width: 0.0, height: 1.0)
        layer.shadowOpacity = 1.0
        layer.shadowRadius = 0.0
    }
}
@IBInspectable public var bottomBorderColor : UIColor = UIColor.clear {
    didSet {

        layer.shadowColor = bottomBorderColor.cgColor
        layer.shadowOffset = CGSize(width: 0.0, height: 1.0)
        layer.shadowOpacity = 1.0
        layer.shadowRadius = 0.0
    }
}
/// Sets the placeholder color
@IBInspectable var placeHolderColor: UIColor? {
    get {
        return self.placeHolderColor
    }
    set {
        self.attributedPlaceholder = NSAttributedString(string:self.placeholder != nil ? self.placeholder! : "", attributes:[NSAttributedString.Key.foregroundColor: newValue!])
    }
}

}

yourTextfield.attributedPlaceholder = NSAttributedString(string: "your placeholder text",attributes: [NSForegroundColorAttributeName: UIColor.white])