AsyncCommand.cs

public abstract class AsyncCommand : Command
{
    public override void Execute(CommandContext context)
    {
        if (context == null)
            return;

        try
        {
            Context.ClientPage.Start(this, "Run", PrepareArgs(context));
        }
        catch (Exception ex)
        {
            Sitecore.Diagnostics.Log.Error(ex.Message, ex, this);
            throw;
        }
    }

    protected virtual NameValueCollection PrepareArgs(CommandContext context)
    {
        var item = context.Items[0];

        var args = new NameValueCollection()
        {
            { "id", item.ID.ToString() },
            { "language", item.Language.ToString() },
            { "version", item.Version.ToString() },
        };

        return args;
    }

    protected abstract void Run(ClientPipelineArgs args);
}