如何使用Url初始化OutputStream？(How to initialise an OutputStream with a Url?)

 我尝试创建一个OutputStream到一个app组文件夹，创建如下： 
 
 func createProjectDirectoryPath(path:String) -> String
    {
        let containerURL = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: "group.xyz")
        let logsPath = containerURL!.appendingPathComponent(path)
        NSLog("12345- folder path: %@", logsPath.path)

        do {
            try FileManager.default.createDirectory(atPath: logsPath.path, withIntermediateDirectories: true, attributes: nil)
        } catch let error as NSError {
            NSLog("12345- Unable to create directory %@", error.debugDescription)
        }
        return logsPath.path
    }
 
 这个函数给了我这样的路径 
 
/private/var/mobile/Containers/Shared/AppGroup/40215F20-4713-4E23-87EF-1E21CCFB45DF/pcapFiles
 
 此文件夹存在，因为行FileManager.default.fileExists（path）返回true。 下一步是将生成的文件名附加到路径，我在这里做 
 
let urlToFile = URL(string: createProjectDirectoryPath(path: "pcapFiles").appending("/\(filename)"))
 
 这给了我正确的新路径 
 
/private/var/mobile/Containers/Shared/AppGroup/40215F20-4713-4E23-87EF-1E21CCFB45DF/pcapFiles/39CC2DB4-A6D9-412E-BAAF-2FAA4AD70B22.pcap
 
 如果我称这行， ostream总是为零 
 
let ostream = OutputStream(url: urlToFile!, append: false)
 
 我错过了什么吗？ OutputStream应该在此路径上创建文件，但由于未知原因，它是不可能的。 
 
 PS：AppGroup在功能和开发人员控制台中启用。 

I try to create an OutputStream to an app group folder, which is created as follows: 
 
 func createProjectDirectoryPath(path:String) -> String
    {
        let containerURL = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: "group.xyz")
        let logsPath = containerURL!.appendingPathComponent(path)
        NSLog("12345- folder path: %@", logsPath.path)

        do {
            try FileManager.default.createDirectory(atPath: logsPath.path, withIntermediateDirectories: true, attributes: nil)
        } catch let error as NSError {
            NSLog("12345- Unable to create directory %@", error.debugDescription)
        }
        return logsPath.path
    }
 
This function gives me a path like this
 
/private/var/mobile/Containers/Shared/AppGroup/40215F20-4713-4E23-87EF-1E21CCFB45DF/pcapFiles
 
This folder exists, because the line FileManager.default.fileExists(path) returns true. The next step is to append a generated filename to the path, which I am doing here
 
let urlToFile = URL(string: createProjectDirectoryPath(path: "pcapFiles").appending("/\(filename)"))
 
which gives me the correct new path
 
/private/var/mobile/Containers/Shared/AppGroup/40215F20-4713-4E23-87EF-1E21CCFB45DF/pcapFiles/39CC2DB4-A6D9-412E-BAAF-2FAA4AD70B22.pcap
 
If I call this line, ostream is always nil
 
let ostream = OutputStream(url: urlToFile!, append: false)
 
Do I miss something? The OutputStream should create the file on this path, but for unknown reason, it is not possible. 
 
PS: AppGroup is enabled in Capabilities and in developers console.

原文：https://stackoverflow.com/questions/44366129