Question

I am receiving an error at this line

return folder.SubFolders.Aggregate(count, (current, subfolder) =>
               GetFilesCount(subfolder, current));

Error is

Error 1 ‘Microsoft.SharePoint.SPFolderCollection’ does not contain a definition for ‘Aggregate’ and no extension method ‘Aggregate’ accepting a first argument of type ‘Microsoft.SharePoint.SPFolderCollection’ could be found (are you missing a using directive or an assembly reference?)

Rest of code is

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Linq;
using System.Windows.Forms;
using Microsoft.SharePoint;
using System.Windows.Controls;
using System.IO;
using System.Collections;

 namespace WindowsFormsApplication1
 {
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                using (SPSite currentSite = new SPSite(txtSiteAddress.Text))
                {
                    SPWeb currentweb = currentSite.OpenWeb();
                    var webtree = new TreeViewItem();
                    webtree.Header = currentweb.Title;
                    webtree.Tag = currentweb;
                    MapFolders(currentweb.Folders, webtree);    
                }
             }
             catch (Exception a)
             {
                MessageBox.Show(a.ToString());
             }
        }

        private void MapFolders(SPFolderCollection folderList,
                                             TreeViewItem treeNode)
        {
            for (var i = 0; i < folderList.Count; i++)
            {
                var item = new TreeViewItem();
                item.Header = string.Format("{0} ({1})", folderList[i].Name,
                                             GetFilesCount(folderList[i], 0));
                item.Tag = folderList[i];

                treeNode.Items.Add(item);

                if (folderList[i].SubFolders.Count > 0)
                    MapFolders(folderList[i].SubFolders, item);
            }
        }

        private int GetFilesCount(SPFolder folder, int count)
        {
            count += folder.Files.Count;

            return folder.SubFolders.Aggregate(count, (current, subfolder) =>
                   GetFilesCount(subfolder, current));
        }



    }
}

I am trying to make a windows form application, as in link below,

enter link description here

I Made Changes to the line to use cast but its says

return folder.SubFolders.Cast(count, (current, subfolder) =>
               GetFilesCount(subfolder, current));

and new Error is

Error 1 No overload for method ‘Cast’ takes ‘2’ arguments

Answer 1

LINQ only works on generic collections.
SPFolderCollection implements IEnumerable, but not IEnumerable<SPFolder>.

You need to call .Cast<SPFolder>().