如何避免强制打开日期 .second 组件？

Question

我正在使用此代码为 macOS 的文档基础应用程序创建一个文档，该文档的名称是自 Date() 引用日期以来经过的秒数。

func saveDocumentInApplicationSupport() {
    do
    {
        // create a directory in Application Support
        let fileManager = FileManager.default
        let appSupportURL = fileManager.urls(for: .applicationSupportDirectory, in: .userDomainMask).first!
        appSupportURL.appendingPathComponent("com.myCompany.myApp")
        let directoryURL = appSupportURL.appendingPathComponent("com.myCompany.myApp").appendingPathComponent("Documents")
        try fileManager.createDirectory (at: directoryURL, withIntermediateDirectories: true, attributes: nil)

        // set a name for the file
        let date = Date(timeIntervalSinceReferenceDate: 0) // "2001-01-01 00:00:00 +0000"
        let seconds = Calendar.current.dateComponents([.second], from: date, to: Date()).second // eg. 517848179

        let fileName = "\(seconds!).idoc" // avoid force unwrapping here
        // eg. 517848179.idoc

        //  Create document
        let documentURL = directoryURL.appendingPathComponent (fileName)
        try document.write (to: documentURL, ofType: "com.myCompany.idoc")
    }
    catch
    {
        print("An error occured")
    }
}

避免强制展开秒变量的正确方法是什么？

Answer 1

我认为你在追逐一条红鲱鱼。你担心这个强制解包，但你的整个代码块都被包围在一个包含多个 try 的 do/catch 中，完全忽略错误，并且几乎没有做任何事情损害控制。

我唯一的建议是将力展开移动到 seconds 的定义：

func saveDocumentInApplicationSupport() {
    do {
        // create a directory in Application Support
        let fileManager = FileManager.default
        let appSupportURL = fileManager.urls(for: .applicationSupportDirectory, in: .userDomainMask).first!
        appSupportURL.appendingPathComponent("com.myCompany.myApp")
        let directoryURL = appSupportURL.appendingPathComponent("com.myCompany.myApp").appendingPathComponent("Documents")
        try fileManager.createDirectory (at: directoryURL, withIntermediateDirectories: true, attributes: nil)

        // set a name for the file
        let date = Date(timeIntervalSinceReferenceDate: 0) // "2001-01-01 00:00:00 +0000"
        let seconds = Calendar.current.dateComponents([.second], from: date, to: Date()).second!

        let fileName = "\(seconds).idoc" // eg. 517848179.idoc

        //  Create document
        let documentURL = directoryURL.appendingPathComponent (fileName)
        try document.write (to: documentURL, ofType: "com.myCompany.idoc")
    }
    catch {
        print("An error occured")
    }
}

强制展开 并不普遍 "bad"。您使用 force unwrap 运算符是完全合理的，因为您只是将 dateComponents 定义为具有 .second 组件。在这种情况下，即使您确实使用条件绑定来 "safely" 展开您的可选，在 nil 情况下您会做什么？

Answer 2

let theDate = Date()

let date = Date(timeIntervalSinceReferenceDate: 0) // "2001-01-01 00:00:00 +0000"
let seconds = Calendar.current.dateComponents([.second], from: date, to: theDate).second!

等同于直接调用：

let seconds = Int(theDate.timeIntervalSinceReferenceDate)

如何避免强制打开日期 .second 组件？

How to avoid to force unwrap a date .second component?

macos

nsdate

swift