茜素iOS还原PlaceHolder

Question

我有一个Xamarin iOS应用程序和一些文本字段，每个文本字段都有一个占位符，当它被选中时被删除，我希望在输入为空或为空时恢复它，如何获得它？

I tried that:

    public override void ViewWillAppear(bool animated)
    {
       base.ViewWillAppear(animated);
       string placeholderAux = txt.Placeholder;
       txt.EditingDidBegin += (object sender, EventArgs e) =>{
           if (string.IsNullOrWhiteSpace(txt.Text))
           {
              txt.Placeholder = placeholderAux;
           }
       };
}

但这不管用

Answer 1

开始编辑时清除占位符。

textField.EditingDidBegin += (object sender, EventArgs e) =>
{
    (sender as UITextField).Placeholder = "";
};

当第一个响应程序更改且字段为空时，重置占位符：

textField.EditingDidEnd += (object sender, EventArgs e) =>
{
    var uITextField = sender as UITextField;
    if (string.IsNullOrEmpty(uITextField.Text))
    {
        uITextField.Placeholder = "StackOverflow";
    }
};