FileManager.contentsEqual 在比较复制的文件时返回 false

Posted 2023-03-07

【中文标题】FileManager.contentsEqual 在比较复制的文件时返回 false

【英文标题】：FileManager.contentsEqual returns false when comparing copied files

【发布时间】：2016-12-13 23:02:18

【问题描述】：

我需要将我的包资源中的 SQLite 文件预加载到应用程序支持目录中。我想确保那里有正确的文件，而不是 Core Data 默认放在那里的空文件。为此，我使用FileManager.default.contentsEqual;但是，这总是返回 false。

我尝试在操场上进行测试，但那里的副本正在创建别名文件，仍然导致 false 比较。

在应用程序中，文件会以相同的名称和大小复制过来。日期不同：副本具有当前日期/时间，而不是原始时间戳。不过，使用contentsEqual，我认为这并不重要。

更新： diff 在命令行显示文件是相同的...

我错过了什么？

---

这是来自 Playground 的代码，与我的应用程序代码几乎相同：

// get the URL for the application support directory
let appSupportDir: URL = try!
 FileManager.default.url(for: FileManager.SearchPathDirectory.applicationSupportDirectory,
                         in: FileManager.SearchPathDomainMask.userDomainMask,
                         appropriateFor: nil, create: true)

// get the source URLs for the preload files
let sqliteFileBundleURL: URL = Bundle.main.url(forResource: "My_DB", withExtension: "sqlite")!
let sqliteShmFileBundleURL: URL = Bundle.main.url(forResource: "My_DB", withExtension: "sqlite-shm")!
let sqliteWalFileBundleURL: URL = Bundle.main.url(forResource: "My_DB", withExtension: "sqlite-wal")!

// create target URLs for copy to application support directory
let sqliteFileAppSptURL: URL = appSupportDir.appendingPathComponent("My_DB.sqlite")
let sqliteShmFileAppSptURL: URL = appSupportDir.appendingPathComponent("My_DB.sqlite-shm")
let sqliteWalFileAppSptURL: URL = appSupportDir.appendingPathComponent("My_DB.sqlite-wal")

// remove the files if they already exist at the target (for test - app doesn't do this)
do 
    let filesFound: [URL] = try FileManager.default.contentsOfDirectory(at: appSupportDir,
                                                                    includingPropertiesForKeys: nil,
                                                                    options: .skipsHiddenFiles)
    if !filesFound.isEmpty 
        for fileURL in filesFound 
            try FileManager.default.removeItem(at: fileURL)
        
        print("Removed \(filesFound.count) files without error.")
    

catch 
    print("Error:\n\(error)")


// copy the files to the application support directory
do 
    try FileManager.default.copyItem(at: sqliteFileBundleURL, to: sqliteFileAppSptURL)
    try FileManager.default.copyItem(at: sqliteShmFileBundleURL, to: sqliteShmFileAppSptURL)
    try FileManager.default.copyItem(at: sqliteWalFileBundleURL, to: sqliteWalFileAppSptURL)

catch 
    print("Error: \(error)")


// compare the copied target files to their source using contentsEqual
let sqliteFileCopied: Bool =
 FileManager.default.contentsEqual(atPath: sqliteFileBundleURL.absoluteString, andPath: sqliteFileAppSptURL.absoluteString)
let sqliteShmFileCopied: Bool =
 FileManager.default.contentsEqual(atPath: sqliteShmFileBundleURL.absoluteString, andPath: sqliteShmFileAppSptURL.absoluteString)
let sqliteWalFileCopied: Bool =
 FileManager.default.contentsEqual(atPath: sqliteWalFileBundleURL.absoluteString, andPath: sqliteWalFileAppSptURL.absoluteString)

【参考方案1】：

啊哈！使用FileManager 时，应该使用path 而不是absoluteString 将URL 转换为String：

// compare the copied target files to their source using contentsEqual
let sqliteFileCopied: Bool =
 FileManager.default.contentsEqual(atPath: sqliteFileBundleURL.path, andPath: sqliteFileAppSptURL.path)
let sqliteShmFileCopied: Bool =
 FileManager.default.contentsEqual(atPath: sqliteShmFileBundleURL.path, andPath: sqliteShmFileAppSptURL.path)
let sqliteWalFileCopied: Bool =
 FileManager.default.contentsEqual(atPath: sqliteWalFileBundleURL.path, andPath: sqliteWalFileAppSptURL.path)

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两者的区别在于path生成的是文件系统类型的路径：

/var/folders/kb/y2d_vrl133d1b04_5kc3kw880000gn/T/com.apple.dt.Xcode.pg/resources/238FF955-236A-42FC-B6EA-9A74FC52F235/My_DB.sqlite

而absoluteString 生成浏览器友好的路径：

file:///var/folders/kb/y2d_vrl133d1b04_5kc3kw880000gn/T/com.apple.dt.Xcode.pg/resources/238FF955-236A-42FC-B6EA-9A74FC52F235/My_DB.sqlite

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注意：path 也可以在游乐场中使用别名文件。