Question

如何从Unmanaged<AnyObject>类型的对象获取Swift类型的值。我的例子是使用ABRecordRef

我在创建ABRecordRef后创建了一个联系对象来管理，但是我在从ObjC转换时遇到了问题。这就是我所拥有的：

init(recordRef: ABRecordRef) {
    if let firstName = ABRecordCopyValue(recordRef, kABPersonFirstNameProperty) {
        self.firstName = firstName

    }
}

如果是ObjC，我会这样做：

CFTypeRef firstNameRef = ABRecordCopyValue(recordRef, kABPersonFirstNameProperty);
if (firstNameRef) {
    self.firstName = (__bridge NSString *)firstNameRef;
}

我似乎找不到正确的向下转换/转换组合，所以任何帮助都会受到赞赏。

Answer 1

由于NoOne在我解决之前回答，我会在这里添加答案：

firstName.takeRetainedValue() as? String

如果你看一下Unmanaged结构类型的标题，你会发现：

/// Get the value of this unmanaged reference as a managed
/// reference and consume an unbalanced retain of it.
///
/// This is useful when a function returns an unmanaged reference
/// and you know that you're responsible for releasing the result.
func takeRetainedValue() -> T

因此，因为CFTypeRef在Swift中转换为Unmanaged<AnyObject>。

Unmanaged使用泛型来定义返回类型，并且声明如下：

Unmanaged<T>

我们的对象属于Unmanaged<AnyObject>类型，这意味着takeRetainedValue()将返回类型T，或者在我们的示例中，键入AnyObject。我使用可选的向下转换，因为我的属性firstName属于String?类型。

您可以使用takeRetainedValue方法从Unmanaged对象中获取价值。在Foundation API中，我猜测它们大部分都是Unmanaged<AnyObject>!类型，并且需要向下转换。通用公式似乎是：

var unmanagedObject: Unmanaged<AnyObject> = someFunctionThatReturnsAnUnmanagedObject()
var newValue: Type = unmanagedObject.takeRetainedValue as Type

Answer 2

import UIKit
import AddressBook

class ViewController: UIViewController {

lazy var addressBook: ABAddressBookRef = {
    var error: Unmanaged<CFError>?
    return ABAddressBookCreateWithOptions(nil, &error).takeRetainedValue() as ABAddressBookRef
}()

@IBAction func GetPeople(sender: UIButton) {
    var ab: ABAddressBookRef = addressBook

    switch ABAddressBookGetAuthorizationStatus(){
    case .Authorized:
        println("Authorized")
        readFromAddressBook(addressBook)
    case .Denied:
        println("Denied")
    case .Restricted:
        println("Restricted")
    case .NotDetermined:
        println("Not determined")
        ABAddressBookRequestAccessWithCompletion(addressBook,
            {[weak self] (granted: Bool, error: CFError!) in
                if granted {
                    let strongSelf = self!
                    println("Access is granted")
                    strongSelf.readFromAddressBook(strongSelf.addressBook)
                }
                else{
                    println("Access is not granted")
                }
        })
    default:
        break
    }
}

func readFromAddressBook(addressBook: ABAddressBookRef){
    let allPeople = ABAddressBookCopyArrayOfAllPeople(addressBook).takeRetainedValue() as NSArray

    for person:ABRecordRef in allPeople{
        if let firstName = ABRecordCopyValue(person, kABPersonFirstNameProperty) {
            if let lastName = ABRecordCopyValue(person, kABPersonLastNameProperty) {
                let ln:String = (lastName.takeRetainedValue() as? String) ?? ""
                let fn:String = (firstName.takeRetainedValue() as? String) ?? ""
                println("\(ln) - \(fn)")
            }
        }
    }
}

}

从Unmanaged <anyobject>获取swift类型的值。例如：ABRecordRef </anyobject>

2 个答案: