在函数示例中，(read|write)DocumentsFromFile(…)拥有一些函数包装器似乎是有意义的，因为OSx和iOS中的所有东西似乎都需要实例化三到四个主要类和一堆属性，配置，链接，实例化和设置，只是为了将“Hi”写入一个文件，在182个国家。
However, these examples aren't complete enough to use in a real program. The write function does not report any errors creating or writing to the file. On the read, I don't think it's a good idea to return an error that the file doesn't exist as the string that is supposed to contain the data that was read. You would want to know that it failed and why, through some notification mechanism, like an exception. Then, you can write some code that outputs what the problem is and allows the user to correct it, or "correctly" breaks the program at that point.
您不会希望只返回一个包含“错误文件不存在”的字符串。然后，您必须在每次调用函数时查找字符串中的错误并在那里处理它。您也可能无法真正判断错误字符串实际上是从实际文件中读取的，还是从代码中生成的。
You can't even call the read like this in swift 2.2 and Xcode 7.3 because NSString(contentsOfFile...) throws an exception. It is a compile time error if you do not have any code to catch it and do something with it, like print it to stdout, or better, an error popup window, or stderr. I have heard that Apple is moving away from try catch and exceptions, but it's going to be a long move and it's not possible to write code without this. I don't know where the &error argument comes from, perhaps an older version, but NSString.writeTo[File|URL] does not currently have an NSError argument. They are defined like this in NSString.h :
public func writeToURL(url: NSURL, atomically useAuxiliaryFile: Bool, encoding enc: UInt) throws
public func writeToFile(path: String, atomically useAuxiliaryFile: Bool, encoding enc: UInt) throws
public convenience init(contentsOfURL url: NSURL, encoding enc: UInt) throws
public convenience init(contentsOfFile path: String, encoding enc: UInt) throws
此外，文件不存在只是程序读取文件时可能遇到的许多潜在问题之一，例如权限问题、文件大小问题或许多其他问题，您甚至不想尝试为每个问题编写处理程序。最好只是假设它都是正确的，并在出现错误时捕获、打印或处理异常，此外，在这一点上，您实际上没有选择。
以下是我的改写:
func writeToDocumentsFile(fileName:String,value:String) {
let documentsPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0] as NSString!
let path = documentsPath.stringByAppendingPathComponent(fileName)
do {
try value.writeToFile(path, atomically: true, encoding: NSUTF8StringEncoding)
} catch let error as NSError {
print("ERROR : writing to file \(path) : \(error.localizedDescription)")
}
}
func readFromDocumentsFile(fileName:String) -> String {
let documentsPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0] as NSString
let path = documentsPath.stringByAppendingPathComponent(fileName)
var readText : String = ""
do {
try readText = NSString(contentsOfFile: path, encoding: NSUTF8StringEncoding) as String
}
catch let error as NSError {
print("ERROR : reading from file \(fileName) : \(error.localizedDescription)")
}
return readText
}
