Collection was modified; enumeration operation may not execute.

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C#

exceptions

Hi,

I am getting an exception when I try to remove item in foreach loop.
Collection was modified; enumeration operation may not execute.

In this short article ( http://www.dotnetperls.com/invalidoperationexception[^] ) they say that it cant be done this way but instead I could implement remove method in my own Plane class. -> but that doesn't work.
Is it possible to do it(to REMOVE item within foreach loop?)

Any comments or suggestions are welcome. Thank you.

// Developed by : XXX XXX

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Threading;

namespace MyApplication
{
    public partial class MainWindow : Window
    {
        // when dealing with time
        DispatcherTimer arrivalClock;
        List<Plane> planes = new List<Plane>();
        List<Plane> planesLanded = new List<Plane>();
        List<Plane> planesCrashed = new List<Plane>();
        Random rnd;

        public MainWindow()
        {
            rnd = new Random(System.Environment.TickCount);
            InitializeComponent();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            arrivalClock = new DispatcherTimer();
            // set the tick interval (pick ranomly between 1 - 5 seconds)
            arrivalClock.Interval = new TimeSpan(0, 0, rnd.Next(1, 5));
            // every time a tick event happens execute the method
            arrivalClock.Tick += new EventHandler(arrivalClock_Tick);
            // all set start the clock now
            arrivalClock.Start();
        }

        void arrivalClock_Tick(object sender, EventArgs e)
        {
            if (planes.Count() != 0)
            {
                // first check for any crashed or landed planes
                foreach (Plane p in planes)
                {
                    if (p.Fuel <= 0)
                    {
                        planesCrashed.Add(p);
                        refreshCrashedList();
                    }
                    else if(p.Distance <= 0)
                    {
                        planesLanded.Add(p);
                        refreshLandedList();
                    }

                    planes.Remove(p);
                    //p.Remove();
                    refreshPlanesList();
                }

                // every existing plane in my list will travel while time passes so their fuel, distance and other properties will change
                foreach(Plane p in planes)
                {
                    p.goForward();
                }
            }

            planes.Add(new Plane());
            refreshPlanesList();
        }

        private void refreshPlanesList()
        {
            lbxLanded.Items.Clear();

            foreach (Plane p in planes)
            {
                lbxLanded.Items.Add(p);
            }
        }

        private void refreshCrashedList()
        {
            lbxCrashed.Items.Clear();

            foreach (Plane p in planesCrashed)
            {
                lbxCrashed.Items.Add(p);
            }
        }

        private void refreshLandedList()
        {
            lbxLanded.Items.Clear();

            foreach (Plane p in planesLanded)
            {
                lbxLanded.Items.Add(p);
            }
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace MyApplication
{
    class Plane
    {
        string callSign;
        byte noOfPassengers;
        int fuelOnBoard;
        int fuelSpent;
        decimal speed;
        decimal distance;
        DateTime arrivedTime;
        Random rnd = new Random();

        // my default / dynamic constructor (i could create anotherone that takes in parameters but there is no need)
        public Plane()
        {
            callSign = getName();
            noOfPassengers = getPassengers();
            fuelOnBoard = getFuelOnBoard();
            fuelSpent = getFuelSpent();
            speed = getSpeed();
            distance = getDistance();
            arrivedTime = DateTime.Now;
        }

        // public properties
        #region

        public int Fuel
        {
            get { return fuelOnBoard; } 
        }

        public decimal Distance
        {
            get { return distance; }
        }

        #endregion

        public override string ToString()
        {
            return String.Format("{0} : passengers = {1}, fuel = {2}, distance = {3}", callSign, noOfPassengers, fuelOnBoard, distance);
        }

        private string getName()
        {
            char c = (char)rnd.Next(65, 91);
            return c.ToString();
        }

        private byte getPassengers()
        {
            byte b = (byte)rnd.Next(0, 255);
            return b;
        }

        private int getFuelOnBoard()
        {
            int i = (int)rnd.Next(2000, 10000);
            return i;
        }

        private int getFuelSpent()
        {
            int i = (int)rnd.Next(200, 1000);
            return i;
        }

        private decimal getSpeed()
        {
            decimal d = (decimal)rnd.Next(140, 400);
            return d;
        }

        private decimal getDistance()
        {
            decimal d = (decimal)rnd.Next(1000, 10000);
            return d;
        }

        public void goForward()
        {
            fuelOnBoard -= rnd.Next(500, 800);
        }

        //public void Remove()
        //{
        //    this.Remove();
        //}
    }
}