Azure webjobs JobHostConfiguration missing and can

I want to rewrite my current webjobs config to the version 3.0 but I can't get it to work with the documentation because I have no idea how to set the dashboardconnectionstring or storageconnectionstring without a config file.

JobHostConfiguration config = new JobHostConfiguration
{
    NameResolver = new WebJobsNameResolver()
};

string defaultStorageConnectionString = string.Format( "Some dynamically generation string" );
config.DashboardConnectionString = defaultStorageConnectionString;
config.StorageConnectionString = defaultStorageConnectionString;

using(JobHost host = new JobHost(config))
{
    // The following code ensures that the WebJob will be running continuously
    host.RunAndBlock();
}

I want to make it run continuously with the correct storage and dashboard connection string, without using a config file.

The 3.0.0 NuGet package update (non-beta) brought breaking changes. It's based on the generic host which is similar to the asp.net host. You could refer to the steps as below:

1.Add this line of code in your program.cs.

.ConfigureAppConfiguration((context, config) => {
    config.AddJsonFile("appsettings.json", optional: false, reloadOnChange: true);
})

The whole code in Program.cs.

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace WebJob1template
{
    class Program
    {
        static void Main()
        {

            var builder = new HostBuilder()
                .UseEnvironment("Development")
                .ConfigureAppConfiguration((context, config) => {
                    config.AddJsonFile("appsettings.json", optional: false, reloadOnChange: true);
                })
                .ConfigureWebJobs(
                b =>
                {
                    b.AddAzureStorageCoreServices()
                    .AddAzureStorage()
                    .AddTimers()
                    .AddFiles();
                    //.AddDashboardLogging();
                })
                .ConfigureLogging((context, b) =>
                {
                    b.SetMinimumLevel(LogLevel.Debug);
                    b.AddConsole();
                })
                .UseConsoleLifetime();


            var host = builder.Build();

            using (host)
            {
                host.Run();
            }
        }
    }
}

2.Set appsettings.json(note that set it's property Copy to Output Directory or Copy always):

{
  "ConnectionStrings": {
    "AzureWebJobsDashboard": "xxxx",
    "AzureWebJobsStorage": "xxxx"
  }
}

3.Functions.cs:

using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;

namespace WebJob1template
{
    public class Functions
    {        
        public static void ProcessQueueMessage([QueueTrigger("queue")] string message, ILogger log)
        {
            //log.WriteLine(message);
            log.LogInformation(message);
        }
    }
}

4.The output:

For more details, you could refer to this tutorial.

Update:

As Joey said, we could use

config.AddInMemoryCollection(settings);

with

public static Dictionary<string, string> settings = new Dictionary<string, string>
{
    {"ConnectionStrings:AzureWebJobsDashboard:0", "xxxxxxx"},
    {"ConnectionStrings:AzureWebJobsStorage:1", "xxxxxx"},
};

So that it will not use the config file. Here is the article about how to use AddInMemoryCollection