问MDCTextInputController错误消息涵盖输入的文本

EN

import MaterialComponents

....

var usernameTextField = MDCTextField()
var userNameTextLayout = MDCTextInputControllerUnderline()
usernameTextField = {
    let usernameTextEdit = MDCTextField()
    usernameTextEdit.translatesAutoresizingMaskIntoConstraints = false
    usernameTextEdit.clearButtonMode = .unlessEditing
    usernameTextEdit.backgroundColor = .white
    return usernameTextEdit
}()
userNameTextLayout.textInput = usernameTextField
userNameTextLayout.placeholderText = "Username"
// add to view
....

private func isUserNameValid() -> Bool {
    let enteredUsername = usernameTextField.text ?? ""
    if (!enteredUsername.isValidEmail) {
        userNameTextLayout.setErrorText("Invalid e-mail address",
                                        errorAccessibilityValue: nil)
        return false
    }
}