FileManager helper 实用方法

func fileInDocumentsDirectory(fileName: String) -> String {
    return getDocumentsURL().appendingPathComponent(fileName).path
}

func getDocumentsURL() -> URL {
    return FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).last!
}

func fileExistsAtPath(path: String) -> Bool {
    return FileManager.default.fileExists(atPath: fileInDocumentsDirectory(fileName: path))
}