ASP.NET Core 2.2 -> 3.0 upgrade. env.IsDevelopment() not found

Question

I upgraded an existing 2.2 project to 3.0. I copied the new code for Program/Startup from a new 3.0 project to my existing 2.2 project. It worked, but the IsDevelopment() below:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env) {    if (env.IsDevelopment())    {       app.UseDeveloperExceptionPage();    } } 

Results in this error:

'IWebHostEnvironment' does not contain a definition for 'IsDevelopment' and the best extension method overload 'HostingEnvironmentExtensions.IsDevelopment(IHostingEnvironment)' requires a receiver of type 'IHostingEnvironment'

The same line did not caused a newly created 3.0 project. What do I need to modify/add to the project upgraded from 2.2?

Answer 1

The new IHostEnvironment, IsDevelopment, IsProduction etc. extension methods are in the Microsoft.Extensions.Hosting namespace which may need to be added to your app.

Reference:

https://docs.microsoft.com/en-us/aspnet/core/migration/22-to-30?view=aspnetcore-3.0&tabs=visual-studio#migrate-startupconfigure

https://github.com/aspnet/AspNetCore/issues/7749