Updating custom header value added as DefaultRequestHeaders of HttpClient

Question

I have a static httpclient shared across requests and I want to add one custom header to it.

httpClient.DefaultRequestHeaders.Add("customHeader", somevalue.ToString());

But I noticed that on every request the value is getting added to that header which I intend to replace on each request. I try to remove the header if it is already exist and add again but it gives me an errors on load test.

if (httpClient.DefaultRequestHeaders.Contains("customHeader"))
        {
            httpClient.DefaultRequestHeaders.Remove("customHeader");
        }
httpClient.DefaultRequestHeaders.Add("customHeader",somevalue.ToString());

Errors -

System.ArgumentException: An item with the same key has already been added.
System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
System.ArgumentNullException: Value cannot be null.

How can I update the custom header value on each request?

Answer 1

The error I was getting: An item with the same key has already been added. Key: x

Example code for mahesh_ing answer:

var request = new HttpRequestMessage
{
    Method = this.method,
    RequestUri = new Uri(this.requestUri),
};

request.Headers.Add("Key", "Value");

var client = new System.Net.Http.HttpClient
{
    Timeout = this.timeout
};

return await client.SendAsync(request);