MapGet

When we create an ASP.NET Core Web Application, we must specify a lambda in the UseEndpoints method in Configure. MapGet calls are often used here.

With this method, we map a pattern to a method call. When the page is accessed in a browser, we can then invoke the method and dynamically generate the page HTML.

An example

Here we modify the Configure method in an ASP.NET Core Web Application. Specify that you want to create an Empty web application in Visual Studio, and then edit Startup.

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Hosting;

namespace WebApplication3 // Date: 3/23/2020.
{
    public class Startup
    {
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseRouting();

            app.UseEndpoints(endpoints =>
            {
                // First MapGet call.
                endpoints.MapGet("/", async context =>
                {
                    await context.Response.WriteAsync("Home");
                });
                // Add a second MapGet call to the endpoints lambda.
                endpoints.MapGet("/bird", async context =>
                {
                    await context.Response.WriteAsync(GetBirdPage());
                });
            });
        }

        string GetBirdPage()
        {
            // Get HTML for bird page.
            return "Bird page";
        }
    }
}
Visit /bird:

Bird page

MapGet in UseEndpoints

We can add multiple MapGet calls in UseEndpoints—the calls to MapGet are enclosed in an anonymous function body. This is compiled into an Action instance.

A summary

By calling MapGet in the lambda expression argument to UseEndpoints, we can specify multiple page URLs. These are resolved by calling asynchronous methods in ASP.NET Core.