如何使用需要返回值的“updateTextAttributes(conversionHandler:)”

Question

Is there anyway to assign this constant a value?

 let conversionHandler : ([NSAttributedString.Key : Any]) -> [NSAttributedString.Key : Any] =  ...    
// how can I assign 


    if #available(iOS 13.0, *) {
        textView.updateTextAttributes(conversionHandler: conversionHandler)
    } else {

    }

Answer 1

Closure expression syntax has the following general form:

{ (parameters) -> return type in
    statements
}

---

Solution

Closure Expression Syntax

let conversionHandler : ([NSAttributedString.Key : Any]) -> [NSAttributedString.Key: Any] = { dictionary in
    return dictionary
}

Shorthand Argument Names

Swift automatically provides shorthand argument names to inline closures, which can be used to refer to the values of the closure's arguments by the names $0, $1, $2, and so on.

If you use these shorthand argument names within your closure expression, you can omit the closure's argument list from its definition, and the number and type of the shorthand argument names will be inferred from the expected function type.

let conversionHandler : ([NSAttributedString.Key : Any]) -> [NSAttributedString.Key: Any] = {
    return $0
}

source: https://docs.swift.org/swift-book/LanguageGuide/Closures.html

Answer 2

let conversionHandler : ([NSAttributedString.Key : Any]) -> [NSAttributedString.Key: Any] = {_ in 
             let font = UIFont.systemFont(ofSize: 72)
            let attributes: [NSAttributedString.Key: Any] = [
                .font: font,
                .foregroundColor: UIColor.red,
            ]

            return attributes
        }