I am using VS 2022, .Net 6.0, and trying to build my first app using System.CommandLine.
Problem: when I build it, I get an error
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.
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!
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.