Ios appendAttributedString返回类型为Void的值

我正在尝试附加两个

NSAttributedString

let string_1 : NSAttributedString = self.answerTextView.attributedText
let string_2 : NSAttributedString = handleHtml(i) // a function that returns a NSAttributedString
let finalStr : NSAttributedString = string_1.mutableCopy().appendAttributedString(string_2)

但我在第三行有个错误：

无法将类型“Void”（aka“（）”的值转换为指定的类型“NSAttributedString”

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我怎样才能解决这个问题？谢谢

appendAttributeString

更新呼叫方。它不会返回新字符串。请尝试以下操作：

let string_1 : NSAttributedString = self.answerTextView.attributedText
let string_2 : NSAttributedString = handleHtml(i) // a function that returns a NSAttributedString
let tmpStr : NSMutableAttributedString = string_1.mutableCopy()
tmpStr.appendAttributedString(string_2)
let finalStr : NSAttributedString = tmpStr.copy()

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例如：

//MARK: Custom functions
func getQueueAttributedString(number N: Int) -> NSAttributedString? {

    let uploadSymbolAttributes = [NSForegroundColorAttributeName: UEColor.brown.six, NSFontAttributeName: UEFont.unearthCharacterFont(13)]

    let attributedString = NSMutableAttributedString(string: UEFontCharacter.triangle_up, attributes: uploadSymbolAttributes)

    let queueAttributes = [NSForegroundColorAttributeName: UEColor.brown.six, NSFontAttributeName: UEFont.museo300(withSize: 13)]

    let queueString = NSAttributedString(string: " \(N) items queued", attributes: queueAttributes)

    attributedString.append(queueString)

    return attributedString

}

其中，

UEFont

是自定义的

UIFont

，

UEColor

是自定义的

UIColor

的静态结构，

UEFontCharacter

是线性图标字体