如何从SKPaymentTransaction获取IAP收据？

Question

如何从用户的iOS设备上的已完成购买中获取应用内购买收据？购买后，我们需要在购买后立即验证收据（最好在SKPaymentTransactionObserver）。否则，当我们尝试单独验证本地收据时......它已经过时了！

以下是我的交易观察员：

extension StoreManager: SKPaymentTransactionObserver {
  func paymentQueue(queue: SKPaymentQueue, updatedTransactions transactions: [SKPaymentTransaction])    {
    print("Received Payment Transaction Response from Apple");
    for transaction:AnyObject in transactions {
      // check object is a transaction first
      if let trans:SKPaymentTransaction = transaction as? SKPaymentTransaction{
        switch trans.transactionState {
        case .Purchased:
          print("Product Purchased");
          SKPaymentQueue.defaultQueue().finishTransaction(transaction as! SKPaymentTransaction)
          // invoke any callback waiting to be called
          purchaseCallbackHolder?([trans.pseudoReceipt]) // here is where I'd like to extract the receipt associated with the transaction
          purchaseCallbackHolder = nil
          break;

        case .Failed:
          print("Purchased Failed");
          SKPaymentQueue.defaultQueue().finishTransaction(transaction as! SKPaymentTransaction)
          break;
        }
      }
    }

  }
}

请注意，上面我写了代码trans.pseudoReceipt。这里的问题是我无法从交易中提取任何收据。但是，当我检查本地收据时...它没有更新！谢谢你的帮助。