Question

以下是我的代码

func contactForUpdates() -> Int {
    //contact server for most recent version
    let versionURL = settings.versionURL

    if let url = URL(string: versionURL) {
        do {
            let contents = try NSString(contentsOf: url, usedEncoding: nil)
//NEXT LINE IS WHERE THE QUESTIONS LIES
            return Int(contents as String)!
        } catch {
            // contents could not be loaded
            processError("Current version could not be loaded.")
            return Int(0)
        }
    } else {
        // the URL was bad!
        processError("Current version could not be loaded--URL was bad.")
        return Int(0)
    }
}

如果加载了URL，它将返回一个整数。糟糕的互联网连接，例如需要在互联网访问之前登录的机场，不会返回整数，而是返回请求登录的完整HTML页面。使用return Int(contents as String)!强制转发，会产生错误fatal error: unexpectedly found nil while unwrapping an Optional value。

我认为这会在我写这个时运行catch语句，但它会返回致命错误。我怎么能抓到这个？

Answer 1

如果0代表您的错误，您可以执行以下操作：

return Int(contents as String) ?? 0

??被称为＆＃34; nil合并运算符＆＃34;。如果它不是nil，则返回第一个值，否则返回第二个值。

如果您想要更强大的处理，可以使用guard ...

guard let value = Int(contents as String) else {
    processError("Something went horribly wrong")
    return 0
}

return value

Answer 2

那是因为您强制将可选值强制为非可选值。

您必须检查转换是否可行：

if let number = Int(contents as String) {
    return number
}
return -1 // Or something you will recognise as error

Answer 3

func contactForUpdates() -> Int {
    //contact server for most recent version
    let versionURL = settings.versionURL

    if let url = URL(string: versionURL) {
        do {
            let contents = try NSString(contentsOf: url, usedEncoding: nil)
            if let vers = Int(contents as String) {
                return vers
            }
            else {
                processError("Current version could not be loaded--Possibly proxy interception")
                return Int(0)
            }
            //return Int(contents as String)!
        } catch {
            // contents could not be loaded
            processError("Current version could not be loaded.")
            return Int(0)
        }
    } else {
        // the URL was bad!
        processError("Current version could not be loaded--URL was bad.")
        return Int(0)
    }
}

修复了错误，尽管do / catch运行了catch语句。我不知道为什么？我希望有人可以回答这个问题，但除此之外，这句话也解决了这个问题。

Swift：确定从字符串转换为整数是否成功

3 个答案: