My System.CommandLine app won't build! It can't find a CommandHandler. Do I need to write-CodePudding

I am using VS 2022, .Net 6.0, and trying to build my first app with System.CommandLine.

Problem: when I build it, I get a complaint that The name 'CommandHandler' does not exist in the current context

The code I'm trying to build is the sample app from the GitHub site: https://github.com/dotnet/command-line-api/blob/main/docs/Your-first-app-with-System-CommandLine.md , without alteration (I think).

It looks like this:

using System;
using System.CommandLine;
using System.IO;

static int Main(string[] args)
{
    // Create a root command with some options
    var rootCommand = new RootCommand
        { 
        new Option<int>(
            "--int-option",
            getDefaultValue: () => 42,
            description: "An option whose argument is parsed as an int"),
        new Option<bool>(
            "--bool-option",
            "An option whose argument is parsed as a bool"),
        new Option<FileInfo>(
            "--file-option",
            "An option whose argument is parsed as a FileInfo")
    };

    rootCommand.Description = "My sample app";

    // Note that the parameters of the handler method are matched according to the names of the options
    rootCommand.Handler = CommandHandler.Create<int, bool, FileInfo>((intOption, boolOption, fileOption) =>
    {
        Console.WriteLine($"The value for --int-option is: {intOption}");
        Console.WriteLine($"The value for --bool-option is: {boolOption}");
        Console.WriteLine($"The value for --file-option is: {fileOption?.FullName ?? "null"}");
    });

        // Parse the incoming args and invoke the handler
        return rootCommand.InvokeAsync(args).Result;
}

I have installed the latest version of System.Commandline: 2.0.0-beta2.21617.1

SURELY I am just being a big fat idiot in some respect. But I don't see it.

Any insight would be welcomed.

CodePudding user response：

This issue is caused by updating the CommandLine 2.0 Beta 2 package. Add the reference System.CommandLine.NamingConventionBinder to the references to fix the problem. Follow the announcements on command-line-api's GitHub account:

> In your project, add a reference to System.CommandLine.NamingConventionBinder.

> In your code, change references to the System.CommandLine.Invocation namespace to
  use System.CommandLine.NamingConventionBinder, where the CommandHandler.Create
  methods are now found. (There’s no longer a CommandHandler type in 
  System.CommandLine, so after you update you’ll get compilation errors until you
  reference System.CommandLine.NamingConventionBinder.)

If you want to continue with the old habits, try using older versions of the System.CommandLine package.

Resources

Announcing System.CommandLine 2.0 Beta 2 and the road to GA

CodePudding user response：

Think you're missing a using line:

using System;
using System.CommandLine;
using System.CommandLine.Invocation;
using System.IO;

I can't swear that's it, but it looks like CommandHandler is defined in a namespace not referenced by a using (in your current code), so System.CommandLine.Invocation may be the key!