Why is this HttpClient usage giving me an "Cannot access a disposed object." error?

Question

I've simplified the code a bit but basically this keep giving me a "Cannot access a disposed object." error and I cant work out why?

I have multiple tasks running simultaneously that perform a GET then parse some HTML then perform a POST depending on the results of the GET.

The method this code resides in returns an event object with results so I don't think I can use await because the method would need to return void?

foreach (Account accountToCheck in eventToCheck.accountsToRunOn)
{
    Task.Run(() =>
    {
        HttpClientHandler handler = new HttpClientHandler();
        CookieContainer cookies = new CookieContainer();
        handler.CookieContainer = cookies;
        using (var client = new HttpClient(handler))
        {
            ServicePointManager.ServerCertificateValidationCallback = delegate (object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) { return true; };
            client.Timeout = new TimeSpan(0, 0, 3);
            client.DefaultRequestHeaders.Add("Keep-Alive", "false");
            HttpResponseMessage response = client.GetAsync("https://test.com", HttpCompletionOption.ResponseContentRead).Result;
            string html = response.Content.ReadAsStringAsync().Result;

            var content = new FormUrlEncodedContent(new[]
            {
                new KeyValuePair<string, string>("test[username_or_email]",  accountToLogIn.accountHandle),
                new KeyValuePair<string, string>("test[password]",           accountToLogIn.accountPassword)
            });

            var loginPostResult = client.PostAsync("https://test.com/login", content).Result;

            loginHTMl = convertToUTF8(loginPostResult.Content.ReadAsStringAsync().Result);
        }
    });
}

Exception.

Unable to read data from the transport connection: Cannot access a disposed object.

Which line is giveing you that exception? Post the entire stack trace in your question. — CathalMF, Apr 18 '16 at 15:52
Can you post the actual stack trace of the exception that you are seeing., — CathalMF, Apr 18 '16 at 15:57
I've edited the question, hopefully that helps a little, let me know what else I can add :-) — Mr J, Apr 18 '16 at 15:58
I think, it is just, because You ran out of scope of Your using, after ReadStringAsync returns. So the loginPostresult is disposed automatically, because of the using directive. — icbytes, Apr 18 '16 at 15:59
In your actual running code is loginPostResult and the convertToUTF8 inside or outside of the Using block? — CathalMF, Apr 18 '16 at 16:03
@icbytes He said he simplified the code. The code posted is not what he is running. — CathalMF, Apr 18 '16 at 16:05
@jamie Remove the using block and see if the problem persists. — CathalMF, Apr 18 '16 at 16:12
Note that this might be one of the few exceptions where the using / dispose pattern isn't best practice - see https://stackoverflow.com/questions/15705092/do-httpclient-and-httpclienthandler-have-to-be-disposed — James Westgate, Jun 27 '18 at 18:26

score 55 · Accepted Answer · answered Apr 18 '16 at 16:20

55

Ok after a bit of research i found the issue. The HttpClientHandler will get disposed after the first request. You need to instruct your system not to dispose the handler.

Change your using to add false to the constructor.

using (var client = new HttpClient(handler, false))
{

}

answered Apr 18 '16 at 16:20

CathalMF

9,705
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3

Weird, I set this but it doesnt seem to make a difference – willem Jan 23 '18 at 14:47
You need to call ReadAsByteArrayAsync between "using" – Ergin Çelik May 22 '18 at 10:45
8

Do not use `HttpClient` in a using statement. https://aspnetmonsters.com/2016/08/2016-08-27-httpclientwrong/ – Sam Rueby Jan 30 '20 at 20:59
@SamRueby and comment author so the best idea is to not use using or to prevent the handler for disposing? – CDrosos Sep 07 '20 at 16:44
@CDrosos as the linked article suggests, it's best to make your `HttpClient` static and to not explicitly dispose. – Sam Rueby Sep 08 '20 at 15:38

score 9 · Answer 2 · answered Apr 19 '16 at 12:56

It's a good practice to reuse HttpClientHandler instance to prevent disposing.

Also personally I prefer more clear syntax with minimizing Task.Result calls.

// single setup of client handler
HttpClientHandler handler = new HttpClientHandler();

var tasks = eventToCheck.accountsToRunOn.Select(async () => {
    // ...
    using (var client = new HttpClient(handler, false)) // pass false to prevent Disposing
    {
        // ...
        var html = await response.Content.ReadAsStringAsync();
        // ...
        return loginHtml;
    }
});

// get array of results
string[] loginsHtml = await Task.WhenAll(tasks);

score 1 · Answer 3 · answered Jun 13 '23 at 22:07

If you are using .NET 6 and Dependency Injection, make sure AddScoped line is before the AddHttpClient line. Example:

builder.Services.AddScoped<IService, Service>();
builder.Services.AddHttpClient<IService, Service>();

Doing the other way around causes the cannot-access-a-disposed-object issue.

score 0 · Answer 4 · answered Apr 27 '21 at 03:37

0

If we are using containers for injecting the Dependency of HttpClient, then "using" is not required. The container will manage the life time by itself

answered Apr 27 '21 at 03:37

Ajith V S

56
3

score 0 · Answer 5 · answered Apr 29 '21 at 16:00

0

Another case I encountered is when operating an Azure Function. When the timeout expires, you get such a message for whatever service you are using.

answered Apr 29 '21 at 16:00

GeorgiG

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Why is this HttpClient usage giving me an "Cannot access a disposed object." error?

5 Answers5

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