制作 HTTPClient PostAsync 和 GetAsync 的正确方法？答案

【问题标题】：Poper way to make a HTTPClient PostAsync and GetAsync?制作 HTTPClient PostAsync 和 GetAsync 的正确方法？
【发布时间】：2019-06-12 16:20:25
【问题描述】：

我想发出一个正确的 HTTPClient 请求。我有一个代码，但我总是收到这样的异常：

Java.IO.IOException：套接字关闭

System.OperationCanceledException：操作已取消。

Java.Net.SocketException：连接重置

Java.Net.SocketException：软件导致连接中止

Java.Net.UnknownHostException：android_getaddrinfo 失败：EAI_NODATA（没有与主机名关联的地址）

Java.Net.UnknownHostException：无法解析主机“tbs.scratchit.ph”：没有与主机名关联的地址

Java.IO.IOException：isConnected 失败：ETIMEDOUT（连接超时）

Java.Net.SocketException：recvfrom 失败：ECONNRESET（对等方重置连接）

我总是遇到这些异常、错误。

我开始想知道如何正确创建 Post Async 和 GetAsync 以避免将来出现这些错误？

以下是我创建 HTTP 客户端的方法：
1. 我有一个类调用 Constants，我将在其中声明一个新的 HTTP 客户端，这样我的项目中只有 1 个 HTTPClient

public class Constants
{
    public static HttpClient client = new HttpClient();
}

2。我有一个函数，它通过 JSON 发送参数，通过 PHP API 从我的服务器获取数据。

public async void FirstTimeSyncUser(string host, string database, string contact, string ipaddress)
    {
        try
        {
            syncStatus.Text = "Checking internet connection";

            string apifile = "first-time-sync-user-api.php";

            if (CrossConnectivity.Current.IsConnected)
            {
                syncStatus.Text = "Initializing first-time user sync";

                var db = DependencyService.Get<ISQLiteDB>();
                var conn = db.GetConnection();

                var getData = conn.QueryAsync<UserTable>("SELECT * FROM tblUser WHERE ContactID = ? AND Deleted != '1'", contact);
                var resultCount = getData.Result.Count;

                var current_datetime = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss");
                int count = 1;

                var settings = new JsonSerializerSettings
                {
                    NullValueHandling = NullValueHandling.Ignore,
                    MissingMemberHandling = MissingMemberHandling.Ignore
                };

                if (resultCount == 0)
                {
                    syncStatus.Text = "Getting user data from the server";

                    var link = "http://" + ipaddress + "/" + Constants.apifolder + "/api/" + apifile;
                    string contentType = "application/json";
                    JObject json = new JObject
                    {
                        { "Host", host },
                        { "Database", database },
                        { "ContactID", contact }
                    };

                     Constants.client.DefaultRequestHeaders.ConnectionClose = true;

                    var response = await Constants.client.PostAsync(link, new StringContent(json.ToString(), Encoding.UTF8, contentType));

                    if (response.IsSuccessStatusCode)
                    {
                        var content = await response.Content.ReadAsStringAsync();

                        if (!string.IsNullOrEmpty(content))
                        {
                            try
                            {
                                var dataresult = JsonConvert.DeserializeObject<List<UserData>>(content, settings);
                                var datacount = dataresult.Count;

                                for (int i = 0; i < datacount; i++)
                                {
                                    syncStatus.Text = "Syncing user " + count + " out of " + datacount;

                                    var item = dataresult[i];
                                    var userid = item.UserID;
                                    var usrpassword = item.UsrPassword;
                                    var usertypeid = item.UserTypeID;
                                    var userstatus = item.UserStatus;
                                    var lastsync = DateTime.Parse(current_datetime);
                                    var lastupdated = item.LastUpdated;
                                    var deleted = item.Deleted;

                                    var insertdata = new UserTable
                                    {
                                        UserID = userid,
                                        UsrPassword = usrpassword,
                                        ContactID = contact,
                                        UserTypeID = usertypeid,
                                        UserStatus = userstatus,
                                        LastSync = lastsync,
                                        LastUpdated = lastupdated,
                                        Deleted = deleted
                                    };

                                    await conn.InsertOrReplaceAsync(insertdata);

                                    count++;
                                }

                                synccount += "Total synced user: " + count + "\n";

                                var logType = "App Log";
                                var log = "Initialized first-time sync (<b>User</b>)  <br/>" + "App Version: <b>" + Constants.appversion + "</b><br/> Device ID: <b>" + Constants.deviceID + "</b>";
                                int logdeleted = 0;

                                Save_Logs(contact, logType, log, database, logdeleted);

                                Preferences.Set("userchangeslastcheck", current_datetime, "private_prefs");

                                FirstTimeSyncSystemSerial(host, database, contact, ipaddress);
                            }
                            catch
                            {
                                var retry = await DisplayAlert("Application Error", "Syncing failed. Failed to send the data.\n\n Error:\n\n" + content + "\n\n Do you want to retry?", "Yes", "No");

                                if (retry.Equals(true))
                                {
                                    FirstTimeSyncUser(host, database, contact, ipaddress);
                                }
                                else
                                {
                                    First_Time_OnSyncFailed();
                                }
                            }
                        }
                        else
                        {
                            Preferences.Set("userchangeslastcheck", current_datetime, "private_prefs");

                            FirstTimeSyncSystemSerial(host, database, contact, ipaddress);
                        }
                    }
                    else
                    {
                        var retry = await DisplayAlert("Application Error", "Syncing failed. Server is unreachable.\n\n Error:\n\n"+ response.StatusCode +" Do you want to retry?", "Yes", "No");

                        if (retry.Equals(true))
                        {
                            FirstTimeSyncUser(host, database, contact, ipaddress);
                        }
                        else
                        {
                            First_Time_OnSyncFailed();
                        }
                    }
                }
                else
                {
                    SyncUserClientUpdate(host, database, contact, ipaddress);
                }
            }
            else
            {
                var retry = await DisplayAlert("Application Error", "Syncing failed. Please connect to the internet to sync your data. Do you want to retry?", "Yes", "No");

                if (retry.Equals(true))
                {
                    FirstTimeSyncUser(host, database, contact, ipaddress);
                }
                else
                {
                    First_Time_OnSyncFailed();
                }
            }
        }
        catch (Exception ex)
        {
            Crashes.TrackError(ex);
            var retry = await DisplayAlert("Application Error", "Syncing failed. Failed to send the data.\n\n Error:\n\n" + ex.Message.ToString() + "\n\n Do you want to retry?", "Yes", "No");

            if (retry.Equals(true))
            {
                FirstTimeSyncUser(host, database, contact, ipaddress);
            }
            else
            {
                First_Time_OnSyncFailed();
            }
        }
    }

3。在获得我需要的数据后，它将通过另一个 POSTASYNC 调用执行另一个函数。在上面的代码中，当我从服务器获取用户数据时，它将执行下一个函数，即 FirstTimeSyncSystemSerial(host, database, contact, ipaddress);

我做错了什么？以及如何改进这一点，以避免这些异常？

【问题讨论】：

所有这些异常似乎都表明互联网连接不好......
所有这些异常似乎要么是坏连接，要么是对我的坏反应！并且与你在Mono 侧的HttpClient 无关...
@SushiHangover 有没有办法改进我的代码以至少避免这些异常？
@G.hakim 有没有办法改进我的代码以至少避免这些异常？
@G.hakim 你能远程我吗？使用 anydesk 来查看我需要做哪些改进？我的 anydesk 是 782 114 930

标签： xamarin xamarin.forms xamarin.android

【解决方案1】：

调试您的代码以找出引发异常的位置。在该代码块周围放置一个 try catch 阻塞。然后捕获所有预期的异常并再次尝试回送一段时间。

【讨论】：

如果您知道自己遇到了可能会被修复的错误，那么使用 try catch 而不是修复问题不是一个合适的答案。这只是“掩盖”问题。

【解决方案2】：

您可以进行通用自定义服务调用，在需要时可以在任何地方调用

 public class RestClient : IRestClient
{
    private const string TokenHeaderKey = "Any Token Header";
    private HttpClient _httpclient = new HttpClient();

    public async Task<T> GetAsync<T>(string url, string token) where T : new()
    {
        var responseContent = await ExecuteRequest(
            async () =>
            {
                try
                {
                    AddTokenToDefaultRequestsHeader(token);
                    return await _httpclient.GetAsync(url);
                }
                finally
                {
                    ClearAuthenticationHeader();
                }
            });

        return await Deserialize<T>(responseContent);
    }

    private void AddTokenToDefaultRequestsHeader(string token)
    {
        _httpclient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(TokenHeaderKey, token);
    }

    private void ClearAuthenticationHeader()
    {
        _httpclient.DefaultRequestHeaders.Authorization = null;
    }

    private static async Task<HttpContent> ExecuteRequest(Func<Task<HttpResponseMessage>> requestFunc)
    {
        HttpResponseMessage response = null;
        try
        {
            response = await requestFunc();
            if (!response.IsSuccessStatusCode)
            {
                var message = $"Executed HTTP request returned status code {response.StatusCode} and reason phrase {response.ReasonPhrase}";

                if (response.StatusCode == HttpStatusCode.Unauthorized)
                {
                    throw new Exception(message);
                }

                throw new Exception(message);
            }

            return response.Content;
        }
        catch (Exception exception)
        {
            if (exception is HttpRequestException || exception is WebException || exception is TaskCanceledException)
            {
                throw new Exception(
                    "Could not connect to service.");
            }

            throw;
        }
    }

    private static async Task<T> Deserialize<T>(HttpContent responseContent) where T : new()
    {
        try
        {
            var responseContentString = await responseContent.ReadAsStringAsync();
            return JsonConvert.DeserializeObject<T>(responseContentString);
        }

        catch (Exception exception)
        {
            if (exception is TaskCanceledException || exception is JsonException)
            {
                throw new Exception("Could not deserialize response content.", exception);
            }
            throw;
        }
    }

并添加一个应用设置类

 public class AppSettings : IAppSettings
{
    public string Server => "server url";
    public string ServerEndPoint => "End point";

    public string Token => "Token If you Have any";
}

然后这样调用

 public class Servicecall 
{
    private readonly IRestClient _restClient;
    private readonly IAppSettings _appSettings;

    public PatientService(IRestClient restClient, IAppSettings appSettings)
    {
        _restClient = restClient;
        _appSettings = appSettings;
    }

    public async Task<IList<PatientViewModel>> GetPatients()
    {
        var url = _appSettings.Server + _appSettings.EndPoint ;
        var token = _appSettings.Token;
        return GetPatientList(await _restClient.GetAsync<List<ListModelClass>>(url, token));
    }

    public IList<Model> GetPatientList(IList<ListModelClass> List)
    {
        return List.Select(p => new Model(p)).ToList();
    }
}

这样你就可以调用不同的服务而不需要输入大量的代码这样您就可以真正轻松地调用服务

【讨论】：

你能把它设计成我的代码吗？这样我就可以了解它的要点
这对你有帮助吗