arrays - 有没有办法获取对象中属性值的数组？

Question

我有一个存储 URL 的对象。在下面的示例中，对象只有 4 个属性，但在我的例子中有更多属性，所以我想知道有没有一种方法可以更优雅地做到这一点。

---

public final class MyObject: NSObject {

  private let firstURL: URL
  private let secondURL: URL
  private let thirdURL: URL
  private let fourthURL: URL

  public func values() -> [URL] {
    return // <--- I need to return URLs from properties like [firstURL, secondURL, thirdURL, fourthURL]
  }
}

我找到了 NSObject 的扩展，可以将属性名称数组作为 String 返回。

Extension Source

public extension NSObject {

  //
  // Retrieves an array of property names found on the current object
  // using Objective-C runtime functions for introspection:
  // https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtPropertyIntrospection.html
  //
  func propertyNames() -> Array<String> {
    var results: Array<String> = []

    // retrieve the properties via the class_copyPropertyList function
    var count: UInt32 = 0
    let myClass: AnyClass = classForCoder
    let properties = class_copyPropertyList(myClass, &count)

    // iterate each objc_property_t struct
    for i in 0..<count {
      if let property = properties?[Int(i)] {
        // retrieve the property name by calling property_getName function
        let cname = property_getName(property)

        // covert the c string into a Swift string
        results.append(cname.debugDescription)
      }
    }

    // release objc_property_t structs
    free(properties)

    return results
  }
}

但它返回属性名称数组，如 ["firstURL", "secondURL", "thirdURL", "fourthURL"]。我想返回值而不是名称。

Answer 1

你可以使用镜像

public final class MyObject: NSObject {
  private let firstURL: URL
  private let secondURL: URL
  private let thirdURL: URL
  private let fourthURL: URL

  public init(firstURL: URL, secondURL: URL, thirdURL: URL, fourthURL: URL) {
    self.firstURL = firstURL
    self.secondURL = secondURL
    self.thirdURL = thirdURL
    self.fourthURL = fourthURL
  }

  public func values() -> [URL] {
    return Mirror(reflecting: self).children.compactMap({ $0.value as? URL })
  }
}

let url = URL(string: "https://stackoverflow.com/")!
let myObject = MyObject(firstURL: url, secondURL: url, thirdURL: url, fourthURL: url)
print(myObject.values()
// [https://stackoverflow.com/, https://stackoverflow.com/, https://stackoverflow.com/, https://stackoverflow.com/]