带回调的.net web服务调用

是否有人知道如何发送各种"回调"参数到web服务，以便，当某个操作完成时，web服务可以调用回调，而无需从操作返回值。

例如，进度百分比，或者更类似于我的问题:

• 你有3种水果(苹果、橙子和柠檬)
• 您询问所有水果(3种水果)的信息

我希望web服务在知道每个水果的答案后立即返回每个值，但同时，保持在相同的动作调用中，所以我没有记录大量不同调用的问题(实际上，有超过3个水果)，因为客户端与日志记录的某些方面进行交互，并且它可能非常令人困惑

 static void ClientFunction()
    {
        WebServiceFunction(Letters.All);
    }
    static bool WebServiceFunction(Letters whatLetters)
    {
        bool checkA = whatLetters == Letters.A, checkB = whatLetters == Letters.B, checkC = whatLetters = Letters.C,
            checkAll = whatLetters == Letters.All;
        //async wrapped
        if(checkA || checkAll)
        {
            // do something A
            // and send the answer to the client as soon as it is known
        }
        //async wrapped
        if (checkB || checkAll)
        {
            // do something B
            // and send the answer to the client as soon as it is known
        }
        //async wrapped
        if (checkC || checkAll)
        {
            // find out something about c
            // and send the answer to the client as soon as it is known
        }

        // lets say this is a generic return value ( for whatever the service does)
        return true;
    }
    enum Letters
    {
        A,
        B,
        C,
        All
    }

谢谢