iOS7 中代替transactionReceipt的方法

if ([UIDevice iOSVersion] > 6.9f) {
        NSURLRequest *urlRequest = [NSURLRequest requestWithURL:[[NSBundle mainBundle] appStoreReceiptURL]];
        NSError *error = nil;
        receiptData = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:nil error:&error];
    }
    else {
        receiptData = transaction.transactionReceipt;

   }

appStoreReceiptURL 是用来获取交易收据的