Question

我开发了一个带有xamarin表单的应用程序。当我让应用程序在后台运行很长时间（2-3小时）时，应用程序将进入一个无法进行任何休息呼叫的状态。它抛出一个未设置为对象实例的＆＃34;对象引用＆＃34;我尝试创建httpClient时出错。

这是代码，

var client = new HttpClient(new NativeMessageHandler());

这是执行我的一个服务调用

声明了一种处理服务调用的通用方法。所以我用var response = await Session.Instance.LoadList<Entity>();

2.it触发此

public Task<GetListResponse<T>> LoadList<T>()
    {
        return LoadList<T>(null);
    }

3.then，

async public Task<GetListResponse<T>> LoadList<T>(GetListRequest request)
    {
        var typeName = typeof(T).Name;

        if (request == null)
        {
            request = new GetListRequest() { Index = 0 };
        }

        var response = await Request<GetListResponse<T>>(string.Format("{0}/list", typeName.ToLower()), Newtonsoft.Json.JsonConvert.SerializeObject(request));

        return response;
    }

最后这里是几个处理api调用的方法，

async public Task<T> Request<T>(string subUrl, string content) where T : ApiResponse
{
    if (content == null)
    {
        System.Diagnostics.Debug.WriteLine("GET. " + subUrl);
        return await Request<T>(subUrl);
    }
    else
    {
        System.Diagnostics.Debug.WriteLine("POST. {0}, Content: {1}", subUrl, content);
        return await Request<T>(subUrl, new StringContent(content, UTF8Encoding.UTF8, "application/json"));
    }
}

请求（）实施，

async public Task<T> Request<T>(string subUrl, HttpContent content = null, int transientRetryCount = 5) where T : ApiResponse'
    {
        try
        {
            HttpResponseMessage response = null;

            using (var client = CreateClient())
            {
                if (content == null)
                    response = await client.GetAsync(Session.Instance.m_url + string.Format("/api/{0}", subUrl));
                else
                    response = await client.PostAsync(Session.Instance.m_url + string.Format("/api/{0}", subUrl), content);
            }

            var responseContent = string.Empty;
            if (response.Content != null)
                responseContent = await response.Content.ReadAsStringAsync();

            if (response.StatusCode != System.Net.HttpStatusCode.OK)
            {
                System.Diagnostics.Debug.WriteLine("Response. {0}, Content: {1}", response.StatusCode, responseContent);

                if ((response.StatusCode == System.Net.HttpStatusCode.BadGateway ||
                    response.StatusCode == System.Net.HttpStatusCode.ServiceUnavailable) && transientRetryCount > 0)
                {
                    //retry...this appears to be a transient error
                    return await Request<T>(subUrl, content, transientRetryCount--);
                }

                return null;
            }

我实际上并没有做任何想象。但无法找到问题所在：/

enter image description here

Answer 1

你的问题与xamarin表格没什么关系。我的猜测是垃圾收集运行并删除了你引用的一个对象。但在不知道你的应用程序的情况下很难分辨。你在测试什么平台？如果是它的android，也许一项服务更适合你的任务。

更新：xamarin表单的网络连接问题

1 个答案: