swift - 这个AnyObject怎么可能？具有 boolValue 属性

Question

我用 Swift 写了一个 NSURL 扩展。

extension NSURL {
  var isDir : Bool {
    do {
      var isDir : AnyObject?
      try self.getResourceValue(&isDir, forKey: NSURLIsDirectoryKey)
      if let result = isDir?.boolValue {
        return result
      } else {
        return false
      }
    } catch {
      return false
    }
  }
}

行得通。但我发现有些人首先将指针(在本例中为 isDIR)“转换”为 NSNumber。例子是:

• NSFileManager list directory contents excluding directories
• NSURL getResourceValue in swift

我发现没有文档说 AnyObject 符合 BooleanType 协议(protocol)。那么我的 Swift 代码如何工作？

Answer 1

Command-点击AnyObject，你会找到答案:

/// The protocol to which all classes implicitly conform.
///
/// When used as a concrete type, all known `@objc` methods and
/// properties are available, as implicitly-unwrapped-optional methods
/// and properties respectively, on each instance of `AnyObject`.  For
/// example:
///
///     class C {
///       @objc func getCValue() -> Int { return 42 }
///     }
///
///     // If x has a method @objc getValue()->Int, call it and
///     // return the result.  Otherwise, return nil.
///     func getCValue1(x: AnyObject) -> Int? {
///       if let f: ()->Int = x.getCValue { // <===
///         return f()
///       }
///       return nil
///     }
///
///     // A more idiomatic implementation using "optional chaining"
///     func getCValue2(x: AnyObject) -> Int? {
///       return x.getCValue?() // <===
///     }
///
///     // An implementation that assumes the required method is present
///     func getCValue3(x: AnyObject) -> Int { // <===
///       return x.getCValue() // x.getCValue is implicitly unwrapped. // <===
///     }
///
/// - SeeAlso: `AnyClass`
@objc public protocol AnyObject {
}

因此，您可以在 AnyObject 实例上调用任何 @objc 方法。

如果你输入

let a: AnyObject?

在 Playground 中，然后:

a?.

自动完成将显示您可以调用的方法的完整列表。而且它巨大。