boxDownloadAllFilesInFolder.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Box.V2.Config;
using Box.V2.JWTAuth;

namespace BoxGetAllUsers
{
    class Program
    {
        static void Main(string[] args)
        {
            ExecuteMainAsync().Wait();
        }
        private static async Task ExecuteMainAsync()
        {
            using (FileStream fs = new FileStream($"./config.json", FileMode.Open))
            {
                var session = new BoxJWTAuth(BoxConfig.CreateFromJsonFile(fs));
                var client = session.AdminClient(session.AdminToken());
                var folderId = "43491738095";
                var folder = await client.FoldersManager.GetInformationAsync(folderId);
                var folderName = folder.Name;
                var localFolderPath = Path.Combine(Directory.GetCurrentDirectory(), folderName);
                ResetLocalFolder(localFolderPath);

                var items = await client.FoldersManager.GetFolderItemsAsync(folderId, 1000, autoPaginate: true);
                var fileDownloadTasks = new List<Task>();
                var files = items.Entries.Where(i => i.Type == "file");
                foreach (var file in files)
                {
                    fileDownloadTasks.Add(client.FilesManager.DownloadStreamAsync(file.Id).ContinueWith((t) =>
                    {
                        var localFile = File.Create(Path.Combine(localFolderPath, file.Name));
                        return t.Result.CopyToAsync(localFile);
                    }));
                }
                await Task.WhenAll(fileDownloadTasks);
            }
        }

        private static void ResetLocalFolder(string localFolderPath)
        {
            if (!Directory.Exists(localFolderPath))
            {
                Directory.CreateDirectory(localFolderPath);
            }
            else
            {
                foreach (var file in Directory.EnumerateFiles(localFolderPath))
                {
                    File.Delete(Path.Combine(localFolderPath, file));
                }
                Directory.Delete(localFolderPath);
                Directory.CreateDirectory(localFolderPath);
            }
        }
    }
}