我开始在MacBook Pro上使用Xamarin Studio开发Xamarin.Forms。我构建了一个应用程序，其目的是查询PrestaShop网站，检索产品并显示它们。
将应用程序部署到Android时，棉花糖以下的版本存在一些问题，但是我已解决了这些问题，因此在此不再赘述。
将应用程序部署到iOS（模拟器）时，我仍然遇到严重问题。该应用程序运行，但是当我单击该按钮以检索数据时，它崩溃，给了我System.ObjectDisposedException，其消息是“ CancellationTokenSource已被处置”。我将在此处粘贴相关的源代码：
async void button1_Click(object sender, System.EventArgs e)
{
try
{
HttpClientHandler hnd = new HttpClientHandler();
hnd.Credentials = new NetworkCredential("[apikey]", "");
string res;
using (var client = new HttpClient(hnd))
{
var responseText = await client.GetStringAsync("[endpoint]/products");
using (MemoryStream stream = new MemoryStream())
using (StreamWriter writer = new StreamWriter(stream))
{
writer.Write(responseText.Replace("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n", string.Empty));
writer.Flush();
stream.Position = 0;
XDocument doc = XDocument.Load(stream);
res = JsonConvert.SerializeXNode(doc, Formatting.Indented, true);
}
var data = JsonConvert.DeserializeObject<Dictionary<string, object>>(res);
//Result.Text = data["products"].GetType().ToString() + Result.Text;
Func<string, Task> creator_method = async (string id) =>
{
try
{
var responseProd = await client.GetStringAsync($"[endpoint]/products/{id}"); // AT THIS ROW THE EXCEPTION IS RAISED!!!
using (MemoryStream stream = new MemoryStream())
using (StreamWriter writer = new StreamWriter(stream))
{
writer.Write(responseProd.Replace("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n", string.Empty));
writer.Flush();
stream.Position = 0;
XDocument doc = XDocument.Load(stream);
res = JsonConvert.SerializeXNode(doc, Formatting.Indented, true);
}
var product_rawData = JsonConvert.DeserializeObject<Dictionary<string, object>>(res);
var productData = (JObject)product_rawData["product"];
try
{
views.Children.Add(new ProductXaml(productData["name"]["language"]["#cdata-section"].ToString(), float.Parse(productData["price"]["#cdata-section"].ToString().Replace('.', ',')), productData["id_default_image"]["@xlink:href"].ToString()));
}
catch (NullReferenceException nre)
{
views.Children.Add(new ProductXaml(productData["name"]["language"]["#cdata-section"].ToString(), float.Parse(productData["price"]["#cdata-section"].ToString().Replace('.', ',')), ""));
}
}
catch (Exception gex) { throw; }
};
foreach (var product in ((JObject)data["products"])["product"])
try
{
Device.BeginInvokeOnMainThread(async () => { await creator_method.Invoke(product["@id"].ToString()); });
}
catch (TaskCanceledException tce) { continue; }
catch (WebException we) { continue;}
}
}
catch (HttpRequestException ex)
{
Result.Text = ex.Message;
}
}
我该如何解决这个问题？
参考方案
“ CancellationTokenSource已被处置”
您的using (var client = new HttpClient())...的CancellationToken似乎已经被第一个client.GetStringAsync()调用所消耗。
如何解决这个问题
我建议您将第二个呼叫放在自己的using块中，以避免出现这种情况。
这是您的代码现在的样子，带有第二个using语句：
async void button1_Click(object sender, System.EventArgs e)
{
try
{
HttpClientHandler hnd = new HttpClientHandler();
hnd.Credentials = new NetworkCredential("[apikey]", "");
string res;
using (var client = new HttpClient(hnd))
{
var responseText = await client.GetStringAsync("[endpoint]/products");
using (MemoryStream stream = new MemoryStream())
using (StreamWriter writer = new StreamWriter(stream))
{
writer.Write(responseText.Replace("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n", string.Empty));
writer.Flush();
stream.Position = 0;
XDocument doc = XDocument.Load(stream);
res = JsonConvert.SerializeXNode(doc, Formatting.Indented, true);
}
var data = JsonConvert.DeserializeObject<Dictionary<string, object>>(res);
//Result.Text = data["products"].GetType().ToString() + Result.Text;
Func<string, Task> creator_method = async (string id) =>
{
try
{
using (var newClient = new HttpClient(hnd)) // Create a new client to avoid your other one's token being consumed
{
var responseProd = await newClient.GetStringAsync($"[endpoint]/products/{id}");
using (MemoryStream stream = new MemoryStream())
using (StreamWriter writer = new StreamWriter(stream))
{
writer.Write(responseProd.Replace("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n", string.Empty));
writer.Flush();
stream.Position = 0;
XDocument doc = XDocument.Load(stream);
res = JsonConvert.SerializeXNode(doc, Formatting.Indented, true);
}
var product_rawData = JsonConvert.DeserializeObject<Dictionary<string, object>>(res);
var productData = (JObject)product_rawData["product"];
try
{
views.Children.Add(new ProductXaml(productData["name"]["language"]["#cdata-section"].ToString(), float.Parse(productData["price"]["#cdata-section"].ToString().Replace('.', ',')), productData["id_default_image"]["@xlink:href"].ToString()));
}
catch (NullReferenceException nre)
{
views.Children.Add(new ProductXaml(productData["name"]["language"]["#cdata-section"].ToString(), float.Parse(productData["price"]["#cdata-section"].ToString().Replace('.', ',')), ""));
}
}
}
catch (Exception gex) { throw; }
};
foreach (var product in ((JObject)data["products"])["product"])
try
{
Device.BeginInvokeOnMainThread(async () => { await creator_method.Invoke(product["@id"].ToString()); });
}
catch (TaskCanceledException tce) { continue; }
catch (WebException we) { continue;}
}
}
catch (HttpRequestException ex)
{
Result.Text = ex.Message;
}
}
希望这可以帮助！ 🙂
当回复有时是一个对象有时是一个数组时，如何在使用改造时解析JSON回复？ - java我正在使用Retrofit来获取JSON答复。这是我实施的一部分-@GET("/api/report/list") Observable<Bills> listBill(@Query("employee_id") String employeeID); 而条例草案类是-public static class…
Mongo汇总 - javascript我的收藏中有以下文件{ "_id": ObjectId("54490b8104f7142f22ecc97f"), "title": "Sample1", "slug": "samplenews", "cat": …
Div单击与单选按钮相同吗？ - php有没有一种方法可以使div上的click事件与表单环境中的单选按钮相同？我只希望下面的div提交值，单选按钮很丑代码输出如下：<input id="radio-2011-06-08" value="2011-06-08" type="radio" name="radio_date&#…
使用Json.NET反序列化复杂对象 - c#我需要反序列化从grogle maps api返回的json：{ "destination_addresses": [ "Via Medaglie D'Oro, 10, 47121 Forlì FC, Italia", "Via Torino, 20123 Milano, Italia",…
将python scikit学习模型导出到pmml - python我想将python scikit-learn模型导出到PMML。哪个python软件包最合适？我阅读了有关Augustus的内容，但是我无法使用scikit-learn模型找到任何示例。 python大神给出的解决方案 SkLearn2PMML是 JPMML-SkLearn命令行应用程序周围的薄包装。有关受支持的Scikit-Learn Estimator和…