问是什么使UIViewController暂时失去响应呢？

EN

// Not calling this from init, so that we can make sure there is a network connection, and only give a single error/alert if there is no network connection.
private func initiateProductFetch(done:(success:Bool)->()) {
    let productIds = self.productsInfo!.productIds()
    if nil == productIds {
        Assert.badMojo(alwaysPrintThisString: "No product Ids!")
    }

    /* Bug #C34, #C39.
    10/30/15; I was having a memory retention issue in regards to the fetchProducts completion handler. The SMIAPStore instance wasn't getting deallocated until the *next* time the store was presented because the store delegate was retaining a reference to the completion handler, which had a strong reference to self (SMIAPStore).
    At first I tried to resolve this by having [unowned self] in the following, but that fails with an exception. Not sure why. And having [weak self] also causes self! to fail-- "fatal error: unexpectedly found nil while unwrapping an Optional value". Why?
    The only way I've found to work around this is to have a selfCopy as below, which is nil'ed out in the completion handler. Seems really clumsy. For consistency sake, and safety sake, I'm also using this technique in the other self.storeDelegate usages in this class.
    */

    var selfCopy:SMIAPStore? = self

    self.storeDelegate?.fetchProducts(productIds!) {
        (products:[SKProduct]?, error:NSError?) in

        Log.msg("\(products)")

        if (products != nil && products!.count > 0 && nil == error) {
            // No error.
            selfCopy!.productsInfo!.products = products
            Log.msg("Done fetching products")
            done(success:true)
        }
        else {
            // Show an error. The VC will not be displayed by now. Returning the error with the done call back will not allow it to be displayed.

            // It seems possible the products are empty and error is nil (at least this occurs in my debug case above).
            var message = ""
            if error != nil {
                message = error!.localizedDescription
            }

            let alert = UIAlertView(title: "Couldn't get product information from Apple!", message: message, delegate: nil, cancelButtonTitle: SMUIMessages.session().OkMsg())
            selfCopy!.userMessageDetails = UserMessage.session().showAlert(alert, ofType: UserMessageType.Error) { buttonNumber in
                done(success:false)
            }
        }

        selfCopy = nil
    }
}

// Call this first to initiate the fetch of the SKProduct info from Apple
public func fetchProducts(productIdentifiers:[String], done: (products:[SKProduct]?, error:NSError?) ->()) {
    self.requestDelegateUseType = .ProductsRequest
    self.productsRequest = SKProductsRequest(productIdentifiers: Set(productIdentifiers))
    self.productsRequest!.delegate = self
    self.fetchProductsCompletion = done
    self.productsRequest!.start()
}

// Seems like this delegate method gets called *before* the requestDidFinish method. Don't really want to rely on that behavior though.
public func productsRequest(request: SKProductsRequest, didReceiveResponse response: SKProductsResponse) {
    Assert.If(.ProductsRequest != self.requestDelegateUseType, thenPrintThisString: "Didn't have a product request")

    if 0 == response.invalidProductIdentifiers.count {

        /*
        #if DEBUG
            // Debugging-- simulate an error fetching products.
            self.fetchProductsCompletion!(products: nil, error: nil)
            return
        #endif
        */

        self.fetchProductsCompletion?(products: response.products, error: nil)
        //self.fetchProductsCompletion = nil
    }
    else {
        let message = "Some products were invalid: \(response.invalidProductIdentifiers)"
        self.fetchProductsCompletion!(products: nil, error: NSError.create(message))
    }
}