- Modern Web Development with ASP.NET Core 3
- Ricardo Peres
- 353字
- 2021-06-18 18:36:04
Logging and diagnostics
As usual, you can obtain a reference to ILogger<T> from the DI framework and use it in your views, like this:
@inject ILogger<MyView> Logger
But there is also another built-in mechanism, the DiagnosticSource class, and property, which is declared in the RazorPage base class. By calling its Write method, you can write custom messages to a diagnostics framework. These messages can be any .NET object, even an anonymous one, and there is no need to worry about its serialization. Have a look at the following code snippet:
@{
DiagnosticSource.Write("MyDiagnostic", new { data = "A diagnostic" });
}
What happens with this diagnostic message is actually somewhat configurable. First, let's add the Microsoft.Extensions.DiagnosticAdapter NuGet package, and then create a custom listener for the events generated for this diagnostic source, like this:
public class DiagnosticListener
{
[DiagnosticName("MyDiagnostic")]
public virtual void OnDiagnostic(string data)
{
//do something with data
}
}
We can add as many listeners as we want, targeting different event names. The actual method name does not matter, as long as it has a [DiagnosticName] attribute applied to it that matches an event name. We need to register and hook it to the .NET Core framework, in the Configure method, by adding a reference to the DiagnosticListener service so that we can interact with it, like this:
public void Configure(IApplicationBuilder app, DiagnosticListener diagnosticListener)
{
var listener = new DiagnosticListener();
diagnosticListener.SubscribeWithAdapter(listener);
//rest goes here
}
Notice that the name in the [DiagnosticName] attribute and DiagnosticSource.Write call match, and also, the name, data, of the anonymous type in the Write call matches the parameter name (and type) of the OnDiagnostic method.
Built-in .NET Core classes produce diagnostics for the following:
- Microsoft.AspNetCore.Diagnostics.HandledException
- Microsoft.AspNetCore.Diagnostics.UnhandledException
- Microsoft.AspNetCore.Hosting.BeginRequest
- Microsoft.AspNetCore.Hosting.EndRequest
- Microsoft.AspNetCore.Hosting.UnhandledException
- Microsoft.AspNetCore.Mvc.AfterAction
- Microsoft.AspNetCore.Mvc.AfterActionMethod
- Microsoft.AspNetCore.Mvc.AfterActionResult
- Microsoft.AspNetCore.Mvc.AfterView
- Microsoft.AspNetCore.Mvc.AfterViewComponent
- Microsoft.AspNetCore.Mvc.BeforeAction
- Microsoft.AspNetCore.Mvc.BeforeActionMethod
- Microsoft.AspNetCore.Mvc.BeforeActionResult
- Microsoft.AspNetCore.Mvc.BeforeView
- Microsoft.AspNetCore.Mvc.BeforeViewComponent
- Microsoft.AspNetCore.Mvc.Razor.AfterViewPage
- Microsoft.AspNetCore.Mvc.Razor.BeforeViewPage
- Microsoft.AspNetCore.Mvc.Razor.BeginInstrumentationContext
- Microsoft.AspNetCore.Mvc.Razor.EndInstrumentationContext
- Microsoft.AspNetCore.Mvc.ViewComponentAfterViewExecute
- Microsoft.AspNetCore.Mvc.ViewComponentBeforeViewExecute
- Microsoft.AspNetCore.Mvc.ViewFound
- Microsoft.AspNetCore.Mvc.ViewNotFound
Hopefully, the names should be self-explanatory. Why would you use this mechanism over the ILogger-based one? This one makes it very easy to add listeners to a diagnostic source, with strongly typed methods. I will talk more about the differences between the two in Chapter 12, Logging, Tracing, and Diagnostics.
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