Swift 中的 throw 是如何通过 'startAccessingSecurityScopedResource()' 声明的？

Question

我会通过当前文件选择器导入数据。我正在查看开发文档并按照它进行操作，但有一个问题。当我不在守卫的条件语句中时，我即将出错，但是'throw'不可用。你如何解决这个问题？

func startAccessingSecurityScopedResource() -> Bool

用法

    func presentDocument(at documentURL: URL) {


        // Start accessing a security-scoped resource.
        guard documentURL.startAccessingSecurityScopedResource() else {
            throw IXError.fileAcessFailed // Error is not handled because the enclosing function is not declared 'throws'
            return
        }

Error is not handled because the enclosing function is not declared 'throws'

我尝试了 guard let 但失败了。

        guard let Acess = documentURL.startAccessingSecurityScopedResource() else { //Initializer for conditional binding must have Optional type, not 'Bool'
            throw IXError.fileAcessFailed // Error is not handled because the enclosing function is not declared 'throws'
            return
        }

IXError

public enum IXError: Error {
    ...
}

*********************************编辑开始 *********** *********************************

我按照答案添加了throws，但是使用它的函数出现了错误

    func documentBrowser(_ controller: UIDocumentBrowserViewController, didPickDocumentURLs documentURLs: [URL]) {
        guard let sourceURL = documentURLs.first else { return }
        presentDocument(at: sourceURL) // Call can throw, but it is not marked with 'try' and the error is not handled
    }
...
    func documentBrowser(_ controller: UIDocumentBrowserViewController, didImportDocumentAt sourceURL: URL, toDestinationURL destinationURL: URL) {
        presentDocument(at: destinationURL) // Call can throw, but it is not marked with 'try' and the error is not handled
    }
...
    func presentDocument(at documentURL: URL) throws {

        guard documentURL.startAccessingSecurityScopedResource() else {
            throw IXError.fileAcessFailed
            return
        }

Error is Call can throw, but it is not marked with 'try' and the error is not handled

Answer 1

Error is not handled because the enclosing function is not declared 'throws'

这指的是您的 presentDocument 函数。像这样声明：

func presentDocument(at documentURL: URL) throws {
...
}

Swift 中的 throw 是如何通过 'startAccessingSecurityScopedResource()' 声明的？

How does throw declare throughs 'startAccessingSecurityScopedResource()' in Swift?

guard

ios

swift