swift - 这个 Swift 语法有什么问题？

Question

我无法弄清楚以下内容有什么问题:

fileprivate func showInlineErrorMessage(_ message: String, forField textField: UITextField) {

        // Show error message
        errorLabel.text   = message
        errorLabel.isHidden = false

        // Highlight field on which the error is
        [usernameTextField, passwordTextField, birthYearTextField, genderTextField].forEach {
            updateHighlightOnTextField($0!, highlight: $0 === textField )
        }
    }

具体部分是$0 === textField

编译器显示以下错误:

"?" must be followed by a call, member lookup, or a subscript

这是旧代码，所以最近似乎有些地方发生了变化。

调用的函数是

fileprivate func updateHighlightOnTextField(_ textField: UITextField, highlight: Bool) {
        let highlightView = textField.superview!
        highlightView.layer.borderWidth = highlight ? 1.0 : 0.0
        highlightView.layer.borderColor = highlight ? DefaultTheme.lineColorError.cgColor : nil
    }

Answer 1

有时 swift 无法理解内联语句的类型。你试过吗:

创建一个外部 bool 值:

    [usernameTextField, passwordTextField, birthYearTextField, genderTextField].forEach {
        let isHighlighted: Bool = ($0 === textField)
        updateHighlightOnTextField($0!, highlight: isHighlighted)
    }