UITextfield leftView as overlay

Question

我正在尝试添加“错误消息”气泡，当用户输入错误的值时，该气泡会出现在文本字段的顶部。我一直在使用.leftView属性工作正常，但它占用textField中的“空格”，将内容推向右侧。将leftView显示为“叠加”而不是字段本身的最佳方法是什么？ （即删除它的界限）

class ValidatedTextField: UITextField {     
override init(frame: CGRect) {
    super.init(frame: frame)

    // Defaults
    maxLength = 40
    layer.sublayerTransform = CATransform3DMakeTranslation(leftPadding, 0, 0)
    backgroundColor = UIColor.whiteColor()

    // Listen in on own text input
    self.addTarget(self, action: "textHasChanged", forControlEvents: UIControlEvents.EditingChanged)
    self.addTarget(self, action: "checkTextValid", forControlEvents: UIControlEvents.EditingDidEnd)
}

override func layoutSubviews() {
    super.layoutSubviews()

    // Add error label message
    labelMessage.frame = CGRectMake(10-leftPadding, -10, self.bounds.size.width-20, 24)
    labelMessage.backgroundColor = .blackColor()
    labelMessage.text = "Message goes here"
    labelMessage.font = UIFont.boldSystemFontOfSize(16)
    labelMessage.textColor = .whiteColor()
    labelMessage.textAlignment = .Center
    labelMessage.layer.cornerRadius = 8
    self.leftView = labelMessage
    self.leftViewMode = .Always
    }
}

Answer 1

所以我想我已经明白了。通过使用leftViewRectForBounds并返回零CGRect，我能够消除它的物理存在。

override func leftViewRectForBounds(bounds: CGRect) -> CGRect {
    return CGRect(x: 0, y: 0, width: 0, height: 0)
}