要从应用商店的应用内购买收据中提取transactionId，您可以使用以下代码示例来实现：

Objective-C示例：

// 导入StoreKit框架
#import 

// 从应用商店的应用内购买收据中提取transactionId的方法
- (NSString *)getTransactionIdFromReceipt:(NSData *)receiptData {
    NSError *error;
    NSDictionary *receipt = [NSJSONSerialization JSONObjectWithData:receiptData options:0 error:&error];
    
    if (error) {
        NSLog(@"Error parsing receipt: %@", error.localizedDescription);
        return nil;
    }
    
    NSArray *inAppPurchases = receipt[@"in_app"];
    
    if (inAppPurchases.count > 0) {
        NSDictionary *latestPurchase = inAppPurchases.lastObject;
        NSString *transactionId = latestPurchase[@"transaction_id"];
        return transactionId;
    }
    
    return nil;
}

Swift示例：

import StoreKit

// 从应用商店的应用内购买收据中提取transactionId的方法
func getTransactionIdFromReceipt(receiptData: Data) -> String? {
    do {
        let receipt = try JSONSerialization.jsonObject(with: receiptData, options: []) as? [String: Any]
        guard let inAppPurchases = receipt?["in_app"] as? [[String: Any]], !inAppPurchases.isEmpty else {
            return nil
        }
        
        let latestPurchase = inAppPurchases.last!
        guard let transactionId = latestPurchase["transaction_id"] as? String else {
            return nil
        }
        
        return transactionId
    } catch {
        print("Error parsing receipt: \(error.localizedDescription)")
        return nil
    }
}

请注意，此代码仅用于从应用商店的应用内购买收据中提取transactionId。您需要确保已经获得了有效的应用内购买收据，并将其传递给上述方法以获取transactionId。