ios - swift 4 : cannot subscript a value of type '[UIFontDesciptor.AttributeName : Any]' with an index of type 'String'

Question

我试图在这里初始化我的自定义字体，但它显示错误。

extension UIFont {
@objc convenience init(myCoder aDecoder: NSCoder) {
    if let fontDescriptor = aDecoder.decodeObject(forKey: "UIFontDescriptor") as? UIFontDescriptor {
        if let fontAttribute = fontDescriptor.fontAttributes["NSCTFontUIUsageAttribute"] as? String { // HERE SHOWING THE ERROR
            var fontName = ""
            switch fontAttribute {
            case "CTFontRegularUsage":
                fontName = appFontName
            case "CTFontEmphasizedUsage", "CTFontBoldUsage":
                fontName = appFontBoldName
            case "CTFontObliqueUsage":
                fontName = appFontItalicName
            default:
                fontName = appFontName
            }
            self.init(name: fontName, size: fontDescriptor.pointSize)!
        }
        else {
            self.init(myCoder: aDecoder)
        }
    }
    else {
        self.init(myCoder: aDecoder)
    }
}
...
}

这非常适用于 swift-3.2。但它没有与 swift-4.0 一起运行。请帮我。提前致谢。

Answer 1

字体属性标识符的类型已从 String 更改为 UIFontDescriptor.AttributeName。

好处是你可以声明一个扩展

extension UIFontDescriptor.AttributeName {
    static let nsctFontUIUsage = UIFontDescriptor.AttributeName(rawValue: "NSCTFontUIUsageAttribute")
}

然后就可以写了

if let fontAttribute = fontDescriptor.fontAttributes[.nsctFontUIUsage] as? String {

或不带扩展名

if let fontAttribute = fontDescriptor.fontAttributes[UIFontDescriptor.AttributeName(rawValue: "NSCTFontUIUsageAttribute")] as? String {