Build status NuGet Samples

Logging to elmah.io from Blazor

Blazor Server App

To start logging to elmah.io from a Blazor Server App, install the Elmah.Io.Extensions.Logging NuGet package:

Install-Package Elmah.Io.Extensions.Logging

dotnet add package Elmah.Io.Extensions.Logging

<PackageReference Include="Elmah.Io.Extensions.Logging" Version="5.*" />

paket add Elmah.Io.Extensions.Logging

In the Program.cs file, add elmah.io logging configuration:

builder.Logging.AddElmahIo(options =>
{
    options.ApiKey = "API_KEY";
    options.LogId = new Guid("LOG_ID");
});

Replace API_KEY with your API key (Where is my API key?) and LOG_ID with the ID of the log you want messages sent to (Where is my log ID?). The package can be configured through settings if you prefer. Check out appsettings.json configuration for details.

All uncaught exceptions are automatically logged to elmah.io. Exceptions can be logged manually, by injecting an ILogger into your view and adding try/catch:

@using Microsoft.Extensions.Logging
@inject ILogger<FetchData> logger

<!-- ... -->

@functions {
    WeatherForecast[] forecasts;

    protected override async Task OnInitAsync()
    {
        try
        {
            forecasts = await Http
                .GetJsonAsync<WeatherForecast[]>("api/SampleData/WeatherForecasts-nonexisting");
        }
        catch (Exception e)
        {
            logger.LogError(e, e.Message);
        }
    }
}

Information and other severities can be logged as well:

@using Microsoft.Extensions.Logging
@inject ILogger<Counter> logger

<!-- ... -->

@functions {
    int currentCount = 0;

    void IncrementCount()
    {
        currentCount++;
        logger.LogInformation("Incremented count to {currentCount}", currentCount);
    }
}

Include details from the HTTP context

Microsoft.Extensions.Logging doesn't know that it is running inside a web server. That is why Elmah.Io.Extensions.Logging doesn't include HTTP contextual information like URL and status code as default. To do so, install the Elmah.Io.AspNetCore.ExtensionsLogging NuGet package:

Install-Package Elmah.Io.AspNetCore.ExtensionsLogging

dotnet add package Elmah.Io.AspNetCore.ExtensionsLogging

<PackageReference Include="Elmah.Io.AspNetCore.ExtensionsLogging" Version="5.*" />

paket add Elmah.Io.AspNetCore.ExtensionsLogging

And add the following code to the Program.cs file:

app.UseElmahIoExtensionsLogging();

Make sure to call this method just before the call to UseRouting and UseEndpoints. This will include some of the information you are looking for.

There's a problem when running Blazor Server where you will see some of the URLs logged as part of errors on elmah.io having the value /_blazor. This is because Blazor doesn't work like traditional websites where the client requests the server and returns an HTML or JSON response. When navigating the UI, parts of the UI are loaded through SignalR, which causes the URL to be /_blazor. Unfortunately, we haven't found a good way to fix this globally. You can include the current URL on manual log statements by injecting a NavigationManager in the top of your .razor file:

@inject NavigationManager navigationManager

Then wrap your logging code in a new scope:

Uri.TryCreate(navigationManager.Uri, UriKind.Absolute, out Uri url);
using (Logger.BeginScope(new Dictionary<string, object> 
{
    { "url", url.AbsolutePath }
}))
{
    logger.LogError(exception, "An error happened");
}

The code uses the current URL from the injected NavigationManager object.

Blazor WebAssembly App (wasm)

To start logging to elmah.io from a Blazor Wasm App, install the Elmah.Io.Blazor.Wasm NuGet package:

Install-Package Elmah.Io.Blazor.Wasm

dotnet add package Elmah.Io.Blazor.Wasm

<PackageReference Include="Elmah.Io.Blazor.Wasm" Version="4.*" />

paket add Elmah.Io.Blazor.Wasm

In the Program.cs file, add elmah.io logging configuration:

builder.Logging.AddElmahIo(options =>
{
    options.ApiKey = "API_KEY";
    options.LogId = new Guid("LOG_ID");
});

Replace API_KEY with your API key (Where is my API key?) and LOG_ID with the ID of the log you want messages sent to (Where is my log ID?).

All uncaught exceptions are automatically logged to elmah.io after calling AddElmahIo. Errors and other severities can be logged manually, by injecting an ILogger into your view and adding try/catch or by implementing error boundaries:

@page "/"
@inject ILogger<Index> logger

@code {
    protected override void OnInitialized()
    {
        logger.LogInformation("Initializing index view");

        try
        {
            object text = "Text";
            var cast = (int)text;
        }
        catch (InvalidCastException e)
        {
            logger.LogError(e, "An error happened");
        }
    }
}

The following may be implemented by the package later:

  • Additional information about the HTTP context (like cookies, URL, and user).
  • Internal message queue and/or batch processing like Microsoft.Extensions.Logging.
  • Support for logging scopes.

Configuration in appsettings.json

Blazor WebAssembly doesn't provide an appsettings.json file as part of the default template. To add one, create a new file named appsettings.json in the wwwroot directory. Make sure to set Build Action to Content and Copy to Output Directory to Copy if Newer. In the file, add the following content:

{
  "ElmahIo": {
    "ApiKey": "API_KEY",
    "LogId": "LOG_ID"
  }
}

As before, API_KEY and LOG_ID should be replaced with real values. In the Program.cs file you can load the config and set up Elmah.Io.Blazor.Wasm using the overloaded AddElmahIo method:

builder.Services.Configure<ElmahIoBlazorOptions>(builder.Configuration.GetSection("ElmahIo"));
builder.Logging.AddElmahIo();

The AddElmahIo mehtod without parameters was introduced in Elmah.Io.Blazor.Wasm v5 package. For earlier versions, provide empty options like this: builder.Logging.AddElmahIo(options => {});

Blazor (United) App

.NET 8 introduces a new approach to developing Blazor applications, formerly known as Blazor United. We have started experimenting a bit with Blazor Apps which have the option of rendering both server-side and client-side from within the same Blazor application. As shown in the sections above, using server-side rendering needs Elmah.Io.Extensions.Logging while client-side rendering needs Elmah.Io.Blazor.Wasm. You cannot have both packages installed and configured in the same project so you need to stick to one of them for Blazor (United) Apps. Since the Elmah.Io.Extensions.Logging package doesn't work with Blazor WebAssembly, we recommend installing the Elmah.Io.Blazor.Wasm package if you want to log from both server-side and client-side. Once the new Blazor App framework matures, we will probably consolidate features from both packages into an Elmah.Io.Blazor package or similar.


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