无法将'UInt'类型的值转换为预期的参数类型'UnsafeMutablePointer< UInt>'

问题描述：

我正在尝试从URL可访问的内容初始化String：

I am trying to initialize a String from the content accessible by a URL:

actualresponse.response = String(contentsOfURL: url, usedEncoding: NSUTF8StringEncoding)

我收到以下错误，指向usedEncoding：

I get the following error thrown, pointing at the usedEncoding:

无法将'UInt'类型的值转换为预期的参数类型'UnsafeMutablePointer'

Cannot convert value of type 'UInt' to expected argument type 'UnsafeMutablePointer'

谁能告诉我为什么会抛出这个错误以及如何解决它？

Can anyone tell me why this error is thrown and how I can fix it?

答

有两种相似但不同的方法可以弄错。

There are two similar but different methods which can be mistaken.

init(contentsOfURL url: NSURL,
    encoding enc: UInt) throws

编码参数采用 NSStringEncoding 值来指定编码，例如

The encoding parameter takes an NSStringEncoding value to specify the encoding, for example

let string = try? String(contentsOfURL:url, encoding:NSUTF8StringEncoding)

The second method retrieves the encoding from the file by passing a pointer as usedEncoding parameter

init(contentsOfURL url: NSURL,
    usedEncoding enc: UnsafeMutablePointer<UInt>) throws

文档说：

返回后，如果成功读取url，则包含使用
来解释数据的编码。

Upon return, if url is read successfully, contains the encoding used to interpret the data.

这意味着您必须传递一个指针，该指针将包含确定的文件编码。

That means you have to pass a pointer which will contain the determined encoding of the file.

var encoding : NSStringEncoding = 0
let string = try? String(contentsOfURL:url, usedEncoding:&encoding)