Swift 数组按属性错误排序：实例方法“localizedCaseInsensitiveCompare”需要“字符串？”符合'StringProtocol'

Question

我正在尝试对这个自定义对象数组进行排序，但出现以下错误：

实例方法“localizedCaseInsensitiveCompare”要求 '细绳？'符合'StringProtocol'

filteredCountriesAndCities?.sorted(by: {$0.countryName?.localizedCaseInsensitiveCompare($1.countryName) == ComparisonResult.orderedAscending})

Answer 1

countryName 为 nil 时需要处理的情况，这里是最后排序 nil 值的示例

let sorted = array.sorted {
    guard let first = $0.countryName else {
        return false
    }
    guard let second = $1.countryName else {
        return true
    }

    return first.localizedCaseInsensitiveCompare(second) == ComparisonResult.orderedAscending
}