UITextField begingofdocument属性返回nil

Question

我以编程方式创建了一个UITextField。现在当我试着得到它的beginningOfDocument属性时，它变成了nil。

代码如下:

public func addTextField(title:String?=nil) -> UITextField {
    kWindowHeight -= 80.0
    let txt: UITextField = UITextField(frame: CGRect(x: 13, y: 67, width: 213.00, height: 35));
    txt.addTarget(self, action: "textFieldDidChange", forControlEvents: UIControlEvents.EditingChanged)
    txt.borderStyle = UITextBorderStyle.RoundedRect
    txt.layer.cornerRadius = 3
    txt.layer.borderColor = UIColorFromRGB(0x1E8ADB).CGColor
    txt.font = UIFont(name: kDefaultFont, size: 14)
    txt.autocapitalizationType = UITextAutocapitalizationType.Words
    txt.clearButtonMode = UITextFieldViewMode.WhileEditing
    txt.layer.masksToBounds = true
    txt.layer.borderWidth = 1.0
    if title != nil  {
        txt.placeholder = title!
    }
    contentView.addSubview(txt)
    return txt
}

在另一个类中，我调用:

let textField = AlertView().addTextField("Send SMS")
var begining = textField.beginingOfDocument

Answer 1

如果您只是创建一个UITextField然后立即尝试访问beginningOfDocument属性或甚至在尝试将其添加到父视图后，您将始终获得uninitialized值。

尝试在UITextField成为第一个响应器后检索该属性并查看结果:-)

好运。