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System.NullReferenceException: 'Object reference not set to an instance of an object.' Microsoft.AspNetCore.Http.IHttpContextAccessor.HttpContext.get

See original GitHub issue

I’m running into this error on startup with a fresh clone of the repo today:

System.NullReferenceException: 'Object reference not set to an instance of an object.'

Microsoft.AspNetCore.Http.IHttpContextAccessor.HttpContext.get

It is coming from here: https://github.com/enkodellc/blazorboilerplate/blob/141cfdc51c6fb4613899483cbe2ff6a8fa38f311/src/Server/BlazorBoilerplate.Server/Startup.cs#L553

I have blazorboilerplate running on another computer without issue. I’m not sure why there’s an error on this one. I’m able to get around the error by patching it with:

diff --git a/src/Server/BlazorBoilerplate.Server/Startup.cs b/src/Server/BlazorBoilerplate.Server/Startup.cs
index 186bd58..cf501a0 100644
--- a/src/Server/BlazorBoilerplate.Server/Startup.cs
+++ b/src/Server/BlazorBoilerplate.Server/Startup.cs
@@ -550,7 +550,7 @@ namespace BlazorBoilerplate.Server
                 // creating the URI helper needs to wait until the JS Runtime is initialized, so defer it.
                 var navigationManager = s.GetRequiredService<NavigationManager>();
                 var httpContextAccessor = s.GetRequiredService<IHttpContextAccessor>();
-                var cookies = httpContextAccessor.HttpContext.Request.Cookies;
+                var cookies = httpContextAccessor.HttpContext == null ? null : httpContextAccessor.HttpContext.Request.Cookies;
                 var httpClientHandler = new HttpClientHandler(){ UseCookies = false };
                 if (_environment.IsDevelopment())
                 {
@@ -558,7 +558,7 @@ namespace BlazorBoilerplate.Server
                     httpClientHandler.ServerCertificateCustomValidationCallback = (message, cert, chain, errors) => { return true; };
                 }
                 var client = new HttpClient(httpClientHandler);
-                if (cookies.Any())
+                if (cookies != null && cookies.Any())
                 {
                     var cks = new List<string>();

Issue Analytics

State:
Created 2 years ago
Comments:7 (4 by maintainers)

Top GitHub Comments

1reaction

oneparametercommented, May 26, 2021

Although this has been a highly debated subject, the consensus is to not rely on the HTTP context anywhere in a Blazor application. What 12step describes in his comment is something in the line of this:

@inject Microsoft.AspNetCore.Http.IHttpContextAccessor HttpContextAccessor
@{
    var cookies = new SomeInitialApplicationStateObject
    {
        SomeCookie = await HttpContextAccessor.HttpContext.Request.Cookies
    };
}
<!DOCTYPE html>
<html lang="en">
<head>
  ....
</head>
<body>
    <app>
        <component type="typeof(App)" render-mode="Server" param-InitialApplicationState="@cookies" />
    </app>
</body>
</html>

That’d expose the cookie to the main component. The only hard part is handling cookie expiration. Since the parameters are only really set during the initial request of the page, you will run into expired cookies at some point in time, if the user keeps their browser open for as long as it takes.

So you might opt to put the whole HTTPContext into the model. Which would be a mistake too, because that would keep the one instance of the http context in memory forever. When you do that, it means no more updates can be done to the HttpContext, no updating of cookies that is. Since the HTTP context cookies cannot be edited when the response has started.

What you really want to do is go with another source of state, don’t use cookies, it will only give you problems.

0reactions

enkodellccommented, Aug 13, 2021

I got this issue on my win7 laptop. Used @EmergentCybernetics adjusted code and it seems work for me until I get back to my win10 box. I am closing issue.