I have a problem with my app. In my computer everything work good. I have problem with app on my notebook. I must debug app but my response doesn't work, this is Exception The operation was canceled. Api work, because i tested in PostMan. My code:
if (httpClient != null)
{
Task<string> response = httpClient.GetStringAsync($"myUrl");
string res = response.GetAwaiter().GetResult();
if (!string.IsNullOrEmpty(res))
{
myModel = JsonConvert.DeserializeObject<Model>(res);
}
}
somebody know why i have a problem on notebook?
Change your code to the following:
if (httpClient != null)
{
string response = await httpClient.GetStringAsync($"myUrl");
if (!string.IsNullOrEmpty(response ))
{
myModel = JsonConvert.DeserializeObject<Model>(response);
}
}
No need to use GetAwaiter()
This method is intended for compiler use rather than for use in application code.
You need to await in async calls, in order to execute the actual call.
Related
I'm posting a bytearray from an Android App in Xamarin.Forms to an .NET Core 2.0 WebAPI. However, I'm getting an exception saying that the NetworkStream already is disposed;
Code making the request;
public async Task PostImageAsync(ImageDTO image)
{
var content = new MultipartFormDataContent();
var byteArrayContent = new ByteArrayContent(image.Content);
content.Add(byteArrayContent, image.FileTile, image.FileName);
try
{
using (var httpClient = GetNewHttpClient())
{
SetBearerToken(httpClient);
var response = await httpClient.PostAsync($"{_apiUrl}/api/images/upload", content);
if (response.IsSuccessStatusCode)
{
}
else
{
}
}
}
catch (Exception e)
{
//Exception occurs here
var msg = e.GetBaseException().Message;
throw;
}
}
Code to get the HttpClient
private HttpClient GetNewHttpClient()
{
//HttpClientHandler is a global variable
var httpClient = new HttpClient(HttpClientHandler, false) {BaseAddress = new Uri(_apiUrl)};
return httpClient;
}
API Endpoint
[HttpPost]
public async Task<IActionResult> Upload(IFormFile file)
{
if (file == null || file.Length == 0) return BadRequest();
return Ok();
}
EDIT - SetBearerToken Method
private static void SetBearerToken(HttpClient client)
{
client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", App.StoredToken);
}
The Exception:
cannot access a disposed object. Object name: 'System.Net.Sockets.NetworkStream'.
It feels like a really obvious mistake I'm making here, but I can't get my head around it. Anybody has any ideas?
Don't dispose objects inside async functions
A using statement in an async method is "odd" in that the Dispose
call may execute in a different thread to the one which acquired the
resource (depending on synchronization context etc) but it will still
happen... assuming the thing you're waiting for ever shows up or
fail, of course. (Just like you won't end up calling Dispose in
non-async code if your using statement contains a call to a method
which never returns.)
#jon-skeet https://stackoverflow.com/a/16566605/2228916
Don’t dispose of the HttpClient:
https://aspnetmonsters.com/2016/08/2016-08-27-httpclientwrong/
Also noticed that you set _apiUrl as the BaseAddress and prefix the url in the post. Pick one or the other.
I am using HttpClient class in my asp.net web api 2 application to post some information to a endpoint. I just want to post the information without waiting for a response. Is this the right syntax
using (var client = new HttpClient())
{
client.BaseAddress = new Uri("http://localhost:9000/");
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
// HTTP POST
var gizmo = new Product() { Name = "Gizmo", Price = 100, Category = "Widget" };
var response = await client.PostAsJsonAsync("api/products", gizmo);
}
I just want to post the information without waiting for a response
Not awaiting an async method in WebAPI will result in a runtime exception, as the AspNetSynchronizationContext is aware of any triggered asynchronous operations. If it notices a controller action completes before the async operation has, it will trigger the said exception. More on that in ASP.NET Controller: An asynchronous module or handler completed while an asynchronous operation was still pending
If you want to use a fire and forget semantics, you need to queue the delegate via HostingEnvironment.QueueBackgroundWorkItem if you're using .NET 4.5.2 and above. If not, you can defer to using BackgroundTaskManager
Keep in mind this kind of design isn't really suitable for WebAPI. It doesn't scale if you're triggering this action call frequently. If this style happens often, consider using something more suitable such as a message broker.
To implement the async Task in ASP.NET refer to the following sample syntax:
protected void Page_Load(object sender, EventArgs e)
{
try
{
RegisterAsyncTask(new PageAsyncTask(LoadUrlContent));
}
catch {}
}
protected async Task LoadUrlContent()
{
try
{
// Add your code here, for example read the content using HttpClient:
string _content = await ReadTextAsync(YourUrl, 10);
}
catch { throw; }
}
Also, set <%# Page ... Async="true" %> at page level.
Following sample code snippet shows the use of HttpClient (call this sample function from LoadUrlContent():
protected async Task<string> ReadTextAsync(string Url, int TimeOutSec)
{
try
{
using (HttpClient _client = new HttpClient() { Timeout = TimeSpan.FromSeconds(TimeOutSec) })
{
_client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("text/html"));
using (HttpResponseMessage _responseMsg = await _client.GetAsync(Url))
{
using (HttpContent content = _responseMsg.Content)
{
return await content.ReadAsStringAsync();
}
}
}
}
catch { throw; }
}
You can modify this code base pertinent to your particular task.
Hope this may help.
Is there anything wrong with my code here? I keep getting this error:
System.InvalidOperationException: The request message was already sent. Cannot send the same request message multiple times.
My HttpRequestMessage is inside a Func so I figured I get a brand new request each time I pass in func().
public async Task<HttpResponseMessage> GetAsync(HttpRequestMessage request)
{
return await RequestAsync(() => request);
}
public async Task<HttpResponseMessage> RequestAsync(Func<HttpRequestMessage> func)
{
var response = await ProcessRequestAsync(func);
if (response.StatusCode == HttpStatusCode.Unauthorized)
{
WaitForSomeTime();
response = await ProcessRequestAsync(func);
}
return response;
}
private async Task<HttpResponseMessage> ProcessRequestAsync(Func<HttpRequestMessage> func)
{
var client = new HttpClient();
var response = await client.SendAsync(func()).ConfigureAwait(false);
return response;
}
You are calling the same func parameter twice:
var response = await ProcessRequestAsync(func);
//...
response = await ProcessRequestAsync(func);
In this case func returns the same request every single time. It doesn't generate a new one every time you call it. If you truly need a different request each time then func needs to return a new message each call:
var response = await GetAsync(() => new HttpRequestMessage()); // Create a real request.
public async Task<HttpResponseMessage> GetAsync(Func<HttpRequestMessage> requestGenerator)
{
return await RequestAsync(() => requestGenerator());
}
I had the same issue, but no repetition in my code. Turned out I had added a watch on an asynchronous process. That watch called the process while I stepped through the code, so that when I got to the line I was trying to debug it crashed with this error message.
Removing all watches solved the problem.
Leaving this here for other people who might have the same problem.
I am looking for c# HTTP client that doesn't throw when it gets an HTTP error (404 for example).
This is not just a style issue; its perfectly valid for a non 2xx reply to have a body but I cant get at it if the HTTP stack throws when doing a GetResponse()
All the System.Net.Http.HTTPClient methods that return Task<HttpResponseMessage> do NOT throw on any HttpStatusCode. They only throw on timeouts, cancellations or inability to connect to a gateway.
If you are using the HttpClient in System.Net.Http, you can do something like this:
using (var client = new HttpClient())
using (var response = await client.SendAsync(request))
{
if (response.IsSuccessStatusCode)
{
var result = await response.Content.ReadAsStreamAsync();
// You can do whatever you want with the resulting stream, or you can ReadAsStringAsync, or just remove "Async" to use the blocking methods.
}
else
{
var statusCode = response.StatusCode;
// You can do some stuff with the status code to decide what to do.
}
}
Since almost all methods on HttpClient are thread safe, I suggest you actually create a static client to use elsewhere in your code, that way you aren't wasting memory if you make a lot of requests by constantly creating a destroying clients for just one request when they can make thousands.
What about implementing a class that is wrapping the HttpClient?
Let it implement the desired methods which are delegated to the client object and try/catch the exceptions in these delegating methods.
class MyClient
{
HttpClient client;
[...]
public String WrappedMethodA()
{
try {
return client.MethodA();
} catch(Exception x) {
return ""; // or do some other stuff.
}
}
}
After implementing your own client, you'll get rid of these exceptions.
If you need a HttpClient instance, inherit from HttpClient and override it's methods it like this:
public String WrappedMethodA()
{
try {
return base.MethodA(); // using 'base' as the client object.
} catch(Exception x) {
return ""; // or do some other stuff.
}
}
I have this line of code
var response = new HttpClient().PostAsJsonAsync(posturi, model).Result;
The Called WebAPI controller returns a bool to make sure the object was saved, but how do I return that bool response?
Continue to get from content:
var httpClient = new HttpClient();
var response = httpClient.PostAsJsonAsync(posturi, model).Result;
bool returnValue = response.Content.ReadAsAsync<bool>().Result;
But, this is really naive approach for quick way to get result. PostAsJsonAsync and ReadAsAsync is not designed to do like this, they are designed to support async await programming, so your code should be:
var httpClient = new HttpClient();
var response = await httpClient.PostAsJsonAsync(posturi, model);
bool returnValue = await response.Content.ReadAsAsync<bool>();
Also, instead of using a flag to check whether an object is saved or not, you should make use of HTTP codes by returning 200 OK to determine that saving is successfully.
The accepted answer is technically correct but blocks the current thread on calls to .Result. If you are using .NET 4.5 or higher, you should avoid that in almost all situations. Instead, use the equivalent asynchronous (non-blocking) version:
var httpClient = new HttpClient();
var response = await httpClient.PostAsJsonAsync(posturi, model);
bool returnValue = await response.Content.ReadAsAsync<bool>();
Note that the method containing the above code needs to be marked async, and should itself be awaited.
Since its an Async operation don't immediately do .Result as its wrong
Instead you need to do it async by doing this:
var httpClient = new HttpClient()
var task = httpClient.PostAsJsonAsync(posturi, model)
.ContinueWith( x => x.Result.Content.ReadAsAsync<bool>().Result);
// 1. GETTING RESPONSE - NOT ASYNC WAY
task.Wait(); //THIS WILL HOLD THE THREAD AND IT WON'T BE ASYNC ANYMORE!
bool response = task.Result
// 2. GETTING RESPONSE - TASK ASYNC WAY (usually used in < .NET 4.5
task.ContinueWith( x => {
bool response = x.Result
});
// 3. GETTING RESPONSE - TASK ASYNC WAY (usually used in >= .NET 4.5
bool response = await task;
NOTE: I just wrote them in here, so I didnt actually test them but more or less that's what you want.
I hope it helps!
I used HttpStatusCode to check the result.
public HttpStatusCode PostStaffPositions(Foo foo)
{
string uri = myapiuri;
using (HttpClient httpClient = new HttpClient())
{
var response = httpClient.PostAsJsonAsync(uri, foo).Result;
return response.StatusCode;
}
}
And then in Controller check it like this:
HttpStatusCode update = staffrest.PostStaffPositions(foo);
if (update == HttpStatusCode.OK)
{
//Update Succeed
}
else
{
//Update Failed
}
If you call the generic version, it should give you back the bool:
var response = new HttpClient().PostAsJsonAsync<bool>(posturi, model).Result;
At least according to the docs.
It's July 2021 and I'm using .net 5 (namely the .net core 5).
I did not see any generic methods above in System.Net.Http. Now the code looks like this (tested):
using (var client = new HttpClient())
{
client.BaseAddress = new Uri("https://localhost:44330/api/Book/Add");
var response = client.PostAsJsonAsync(client.BaseAddress,
JsonSerializer.Serialize(_teamSummaries));
MessageBox.Show(#"Result is " + JsonSerializer.Serialize(response));
var returnValue = response.Result.Content.ReadAsStringAsync();
MessageBox.Show(#"Return value is " + returnValue.Result);
}
There are also ReadAsStringAsync, ReadAsByteArrayAsync, ReadAsStream, ReadFromJsonAsync, ReadFromJsonAsync<T> (this method returns Task<T>).
But from the text meaning "ReadFromJsonAsync", I think the T is not the bool mentioned above, but a class that contains the bool member. If you want to return something like book, give it a try.
On the other hands, since code on the server looks like this(.net 5):
[HttpPost]
[Route("Add")]
public async Task<ActionResult<IEnumerable<Book>>> Add(string value)
{
var all = await _dbCollection.FindAsync(Builders<Book>.Filter.Empty);
return Ok("Everything is ok.");
}
So, if we want to return true by bool, we should return Ok(...). If we want to return false by bool, we should return something else. There are more than 20 other types of results, which contains much more information rather than just "false".