AspNetCore.Docs/aspnetcore/blazor/fundamentals/logging.md

title	author	description	monikerRange	ms.author	ms.custom	ms.date	no-loc	uid
ASP.NET Core Blazor logging	guardrex	Learn about logging in Blazor apps, including log level configuration and how to write log messages from Razor components.	>= aspnetcore-3.1	riande	mvc	06/10/2020	ASP.NET Core Identity cookie Cookie Blazor Blazor Server Blazor WebAssembly Identity Let's Encrypt Razor SignalR	blazor/fundamentals/logging

ASP.NET Core Blazor logging

Blazor WebAssembly

Configure logging in Blazor WebAssembly apps with the WebAssemblyHostBuilder.Logging property in Program.Main:

using Microsoft.AspNetCore.Components.WebAssembly.Hosting;

...

var builder = WebAssemblyHostBuilder.CreateDefault(args);

builder.Logging.SetMinimumLevel(LogLevel.Debug);
builder.Logging.AddProvider(new CustomLoggingProvider());

The Logging property is of type xref:Microsoft.Extensions.Logging.ILoggingBuilder, so all of the extension methods available on xref:Microsoft.Extensions.Logging.ILoggingBuilder are also available on Logging.

Logging configuration can be loaded from app settings files. For more information, see xref:blazor/fundamentals/configuration#logging-configuration.

Blazor Server

For general ASP.NET Core logging guidance, see xref:fundamentals/logging/index.

Blazor WebAssembly SignalR .NET client logging

Inject an xref:Microsoft.Extensions.Logging.ILoggerProvider to add a WebAssemblyConsoleLogger to the logging providers passed to xref:Microsoft.AspNetCore.SignalR.Client.HubConnectionBuilder. Unlike a traditional xref:Microsoft.Extensions.Logging.Console.ConsoleLogger, WebAssemblyConsoleLogger is a wrapper around browser-specific logging APIs (for example, console.log). Use of WebAssemblyConsoleLogger makes logging possible within Mono inside a browser context.

@using Microsoft.Extensions.Logging
@inject ILoggerProvider LoggerProvider

...

var connection = new HubConnectionBuilder()
    .WithUrl(NavigationManager.ToAbsoluteUri("/chathub"))
    .ConfigureLogging(logging => logging.AddProvider(LoggerProvider))
    .Build();

Log in Razor components

Loggers respect app startup configuration.

The using directive for xref:Microsoft.Extensions.Logging is required to support Intellisense completions for APIs, such as xref:Microsoft.Extensions.Logging.LoggerExtensions.LogWarning%2A and xref:Microsoft.Extensions.Logging.LoggerExtensions.LogError%2A.

The following example demonstrates logging with an xref:Microsoft.Extensions.Logging.ILogger in Razor components:

@page "/counter"
@using Microsoft.Extensions.Logging;
@inject ILogger<Counter> logger;

<h1>Counter</h1>

<p>Current count: @currentCount</p>

<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>

@code {
    private int currentCount = 0;

    private void IncrementCount()
    {
        logger.LogWarning("Someone has clicked me!");

        currentCount++;
    }
}

The following example demonstrates logging with an xref:Microsoft.Extensions.Logging.ILoggerFactory in Razor components:

@page "/counter"
@using Microsoft.Extensions.Logging;
@inject ILoggerFactory LoggerFactory

<h1>Counter</h1>

<p>Current count: @currentCount</p>

<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>

@code {
    private int currentCount = 0;

    private void IncrementCount()
    {
        var logger = LoggerFactory.CreateLogger<Counter>();
        logger.LogWarning("Someone has clicked me!");

        currentCount++;
    }
}

Additional resources

• xref:fundamentals/logging/index