Swift AnyObject作为字符串动态强制转换失败

Question

我有一个Int，作为AnyObject保存在Parse中。当我检索AnyObject时？尝试将其转换为字符串、NSString、NSNumber或其他任何形式，我不断得到一个EXC_断点，因为转换返回Nil，并且出现“Swift dynamic cast failed”错误。

我试图创建这个简单的测试来找出哪个部分失败了，但疯狂的是，这个测试将通过似乎所有步骤都相同的地方：

func testAnyObjectCasting(){
    var myInt32: Int32 = 265
    var myInt: Int = Int(myInt32)
    var myAnyObject: AnyObject? = myInt as AnyObject
    var myAnyArray: [[AnyObject]] = [[AnyObject]]()
    myAnyArray.append(["something", myAnyObject!])
    println(myAnyObject)
    var myOtherAnyObject: AnyObject? = myAnyArray[0][1]
    println(myOtherAnyObject)
    var myString:NSNumber? = myOtherAnyObject as? NSNumber
    println(myString)
    var myInt2: Int = myString! as Int
}

以下是我的逻辑中的相关代码片段，并注意到println（）在向下转换到NSNumber之前工作正常，此时返回Nil：

   //ABRecordGetRecordId returns an ABRecordID, which is of type Int32
   //This value that's stored in the 2nd column of the multiDim [[AnyObject]] 
   var personId: Int = Int(ABRecordGetRecordID(person))

   //This is a call to a Parse object, which returns an AnyObject.  I then cast that to
   //a multidimensional array AnyObject as that's the true structure of the data in swift speak
   var deviceContacts: [[AnyObject]] = device?[deviceContactsFieldName] as [[AnyObject]]

   //This returns the expected value, which in my broader test case is 99999, which is supported by Int
   var i:Int = 1
   println("the value in device contacts \(i) column 1 is: \(deviceContacts[i][1])")

   //This takes a single cell value from the multidim array and puts it in an optional AnyObject
   var valueInParse: AnyObject? = deviceContacts[i][1]

   //This still returns 99999
   println(valueInParse)

   //This is where 99999 is replaced with nil.  Any ideas?
   var valueNSNumberInParse: NSNumber? = valueInParse as? NSNumber

   //Nil :(
   println(valueNSNumberInParse)

   //Exception as I'm trying to unwrap nil :( 
   var unwrappedNSNumber:NSNumber = valueNSNumberInParse!

我的一部分挫败感是，我不明白为什么println（）对任何对象都很好，但所有的转换都失败了。显然，有一些代码可以将该值解释为println的字符串，但我无法正确转换该语法。

Answer 1

因为您已将Int保存到Parse中，并且Int不是对象，所以必须将其转换为对象。似乎解析框架已将其转换为NSValue，NSValue实际上是一个表示内在类型的字节缓冲区。

您可以尝试将这些字节转换回Int，但是在将其存储在Parse对象中之前，将值编码为NSNumber更容易也更好——然后在检索对象时，您将能够轻松处理它。