Asp.net-core – ASP.NET Core 2.2 -> 3.0 upgrade. env.IsDevelopment() not found

I have resolved this problem after asking the same question.

You must either remove SWT.VIRTUAL or update to the SVN build of SWT. I've posted a bug report on the SWT bug page.

Edit: your code snippet has a bug in it that is causing the ArrayIndexOutOfBoundsException. You can resolve it by changing lines containing listenerSD:

public void handleEvent(Event event) {
    Collection<?> collectionW = (Collection<?>) event.widget
            .getData(DATA_COLLECTION);
    if (collectionW.size() > event.index) {
        Object object = collectionW
                .toArray(new Object[collectionW.size()])[event.index];
        ((TableItem) event.item).setText(0, object
                .toString());
    }
}

As part of ASP.NET Core 3.0, the team moved away from including Json.NET by default. You can read more about that in general in the announcement on breaking changes to Microsoft.AspNetCore.App.

Instead of Json.NET, ASP.NET Core 3.0 and .NET Core 3.0 include a different JSON API that focuses a bit more on performance. You can learn about that more in the announcement about “The future of JSON in .NET Core 3.0”.

The new templates for ASP.NET Core will no longer bundle with Json.NET but you can easily reconfigure the project to use it instead of the new JSON library. This is important for both compatibility with older projects and also because the new library is not supposed to be a full replacement, so you won't see the full feature set there.

In order to reconfigure your ASP.NET Core 3.0 project with Json.NET, you will need to add a NuGet reference to Microsoft.AspNetCore.Mvc.NewtonsoftJson, which is the package that includes all the necessary bits. Then, in the Startup’s ConfigureServices, you will need to configure MVC like this:

services.AddControllers()
    .AddNewtonsoftJson();

This sets up MVC controllers and configures it to use Json.NET instead of that new API. Instead of controllers, you can also use a different MVC overload (e.g. for controllers with views, or Razor pages). That AddNewtonsoftJson method has an overload that allows you to configure the Json.NET options like you were used to with AddJsonOptions in ASP.NET Core 2.x.

services.AddControllers()
    .AddNewtonsoftJson(options =>
    {
        options.SerializerSettings.ContractResolver = new DefaultContractResolver();
    });