Winform递归循环-一次又一次调用方法[关闭]

Question

请随意创建一个 Windows 窗体应用程序。要重现错误，请禁用网络连接并运行代码。它每 1 秒尝试重新连接一次。在 4-5 次尝试启用网络连接后，在调试模式下，您会注意到 Reconnect() 方法被调用了 4-5 次，即使产品已被获取。获取产品后为什么要一次又一次地调用 Reconnect() 方法？

        string apiUrl = "https://api.gdax.com/products";
        string json;

        private void Form1_Load(object sender, EventArgs e)
        {            
            try
            {                
                if (FillProducts()) // product need first
                {
                }
            }
            catch (WebException ex)
            {
                ReconnectOnError(ex);
            }
        }
        private bool FillProducts()
        {
            bool isDone = false;
            try
            {
                json = GetGDXJSONData(apiUrl);
                JsonSerializer serializer = new JsonSerializer();
                DataTable dt = (System.Data.DataTable)Newtonsoft.Json.JsonConvert.DeserializeObject(json, (typeof(System.Data.DataTable)));

                count = dt.Rows.Count;

                if (count > 0)
                    isDone = true;
            }
            catch (Exception ex)
            {               
                isDone = false;
                ReconnectOnError(ex);
            }
            return isDone;
        }

        int count = 0;
        private void ReconnectOnError(Exception errorMessage)
        {
            try
            {
                Thread.Sleep(1000);
                if (count < 1)
                {
                    FillProducts();     // it comes on this point again and again even the count is greater than 1
                    Reconnect();
                }
                else
                {
                    Reconnect();
                }
            }
            catch (WebException ex)
            {
                ReconnectOnError(ex);
            }
        }

        private void Reconnect()
        {
            // why this is called the number of times the attempt was made to fill the products?
        }      

        private string GetGDXJSONData(string apiUrl)
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(apiUrl);

            request.Method = "GET";
            request.ContentType = "application/json";
            request.UserAgent = "gdax-node-client";
            request.Accept = "application/json";

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            string responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();

            return responseString;
        }
    }

编辑 - 这是一个示例代码，一旦获取产品，我将在 Reconnect() 方法中做很多事情。 此外，如果在获取产品后发生错误，则不要获取产品，只需调用 Reconnect() 方法，这就是 else 的原因。

Edit2 - 请不要仅仅通过查看代码来回复。如果您创建了一个表单并自己运行它并且可以自己看到错误，那么请告知如何解决此问题。

更新 - 我知道我进入了无限迭代。我试过了，现在可以了：

    string apiUrl = "https://api.gdax.com/products";
    string json;

    private void Form1_Load(object sender, EventArgs e)
    {
        if (FillProducts()) // product need first
        {
        }
    }

    bool isOk = false;
    private string GetGDAXProducts()
    {
        try
        {
            json = GetGDXJSONData(apiUrl);
            return json;
        }
        catch (Exception ex)
        {               
            return "-1";
        }
    }

    int count = 0;
    private bool FillProducts()
    {
        bool isDone = false;
        string retVal = GetGDAXProducts();

        while (retVal == "-1")
        {
            retVal = GetGDAXProducts();
        }

        if (retVal != "-1")
        {
            JsonSerializer serializer = new JsonSerializer();
            DataTable dt = (System.Data.DataTable)Newtonsoft.Json.JsonConvert.DeserializeObject(json, (typeof(System.Data.DataTable)));

            count = dt.Rows.Count;

            if (count > 0)
                isDone = true;
        }

        return isDone;
    }

    private string GetGDXJSONData(string apiUrl)
    {
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(apiUrl);

        request.Method = "GET";
        request.ContentType = "application/json";
        request.UserAgent = "gdax-node-client";
        request.Accept = "application/json";

        HttpWebResponse response = (HttpWebResponse)request.GetResponse();
        string responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();

        return responseString;
    }

Answer 1

你这里有一个无意的循环：

如果FillProducts失败，它会调用自己...

1. 迭代：FP 失败
2. 迭代：FP 调用 ReconnectOnEx 调用 FP，再次失败
3. 迭代：FP 调用 ReconnectOnEx 调用 FP 调用 ReconnectOnEx ...

n.迭代：....调用成功并返回的FP。

现在整个堆栈将随着每次迭代调用 Reconnect 展开。

private bool FillProducts()
    {
        bool isDone = false;
        try
        {
            /* ... Fails if no connection ... */
        }
        catch (Exception ex)
        {               
            isDone = false;
            ReconnectOnError(ex); // ==> BLOCKS !!
        }
        return isDone;
    }

    int count = 0;
    private void ReconnectOnError(Exception errorMessage)
    {
        try
        {
            Thread.Sleep(1000);
            if (count < 1)
            {
                FillProducts();     // <== Will result in another call to this method. Returns on 1st Succeeding call to FillProducts.
                Reconnect();        // <== Will be called as soon as FillProducts returns.
            }
            else
            {
                Reconnect();
            }
        }
        catch (WebException ex)
        {
            ReconnectOnError(ex);
        }
    }

为避免这种情况，您可以将“重试”逻辑移到 FillProducts 方法中：

private bool FillProducts()
    {
        // To prevent waiting forever ...
        int retryCount = 10;

        bool isDone = false;
        while ( !isDone && (retryCount-- > 0) )
        {
            try
            {
                /* ... Fails if no connection ... */

                // OnSuccess=>
                isDone = true; // will break the loop.
            }
            catch (Exception ex) // You should actually catch a more specific Exception here
                                 // ... but that's a different question.
            {               
                isDone = false;
                // Just omit this! >>> ReconnectOnError(ex); // ==> BLOCKS !!
                // If you want, you can add a little delay here ...
                Thread.Sleep(1000);
                // From your code, I guess this has to be called on failure ...
                Reconnect();
            }
        }
        return isDone;
    }

需要考虑的其他几点：

1. 您不应该在 GUI 线程上执行网络 I/O。您的 GUI 可能会变得无响应。考虑使用 async/await（任务异步模式）

2. 捕捉Exception 可能不是最好的主意。您应该尽可能捕捉到最具体的异常，其余的则由调用者处理。

Answer 2

当没有互联网连接时。计数变量总是为零。

Answer 3

这是因为如果没有网络连接，那么调用 API url 将无法连接，并且在您的 catch 块中您正在尝试重新连接

        catch (Exception ex)
        {               
            isDone = false;
            ReconnectOnError(ex);
        }