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Asp.net – Reference to IExceptionHandler interface not being resolved from Microsoft.AspNetCore.Diagnostics

I am adding a global exception handling project to my solution and have installed the Microsoft.AspNetCore.Diagnostics NuGet package. Although the package is recognized and listed in the project’s dependencies, I encounter an error when trying to use the IExceptionHandler interface. The error message is:

CS0234: The type or namespace name 'IExceptionHandler' does not exist in the namespace 'Microsoft.AspNetCore.Diagnostics' (are you missing an assembly reference?)

I am sharing this because similar issues on StackOverflow don’t address problems specific to the Microsoft.AspNetCore.Diagnostics package. Other references, like Microsoft.AspNetCore.Mvc and System.Data.SqlClient, resolve fine for my project. An older but similar issue was posted here. However, it does not exactly match my scenario.

Here are a few observations:

  • Uninstalling the Microsoft.AspNetCore.Diagnostics package doesn’t cause VS to flag the using statement.

  • A working project doesn’t have this package in its dependencies, which is puzzling.

  • I have reset VS settings, cleared caches, and reinstalled VS, but the issue persists.

  • The project builds despite the errors, which is also confusing.

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2

Answers


  1. Chosen as BEST ANSWER
    0

    Adding the following code in my .csproj file resolved the issue:

    <ItemGroup>
<PackageReference Include="Microsoft.AspNetCore.App" />

    I'd appreciate it if someone could explain what was wrong and how this fix resolved the issue.


  2. 0

    If you want to handle exceptions in a custom class, you still need to register it. As mentioned on this article, if you have a class CustomExceptionHandler you need to add it to the IServiceCollection like the example below:

    var builder = WebApplication.CreateBuilder(args);

builder.Services.AddExceptionHandler<CustomExceptionHandler>();

var app = builder.Build();

if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
}

    Here the address "/Error" can be replaced by any page you want to use as error handling. If you don’t call the UseExceptionHandler, the WebApplication won’t be able to redirect the user to an error handling page.

    If you wish to leave error redirection to another software (eg. Nginx) you should call the method UseStatusCodePages like the example below:

    var builder = WebApplication.CreateBuilder(args);

builder.Services.AddExceptionHandler<CustomExceptionHandler>();

var app = builder.Build();

app.UseStatusCodePages();

    Further examples can be found on the aforementioned Microsoft documentation.

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