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

问题描述：

我需要将SQLite文件从我的包资源中预加载到应用程序支持目录中。我想确保正确的文件与Core Data默认放置的空文件相对应。为此，我使用FileManager.default.contentsEqual;但是，这始终返回false。FileManager.contentsEqual在比较复制文件时返回false

我试着用游乐场进行测试，但是那里的副本创建了别名文件，仍然导致了false的比较。

在应用程序中，文件使用相同的名称和大小进行复制。日期不同：副本具有当前日期/时间而不是原始时间戳。然而，使用contentsEqual，我不会认为这个问题。

更新：diff在命令行中显示文件是相同的......

我缺少什么？

下面是操场，这几乎是一样的我的应用程序代码的代码：

// 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)

答

啊哈！当使用FileManager，人们应该使用path而非absoluteString转换一个URL到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)

这两者之间的区别是，path生成一个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生成浏览器友好路径：

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

注：path还与别名文件的游乐场。

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

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