I have created a indexer and I tried to set value for it but it keeps showing index out of range exception

Question

I have created a class called AirlineCompany which attribute have a collection of flight information. To have flight information, I created a class called Flight. Then in the AirlineCompany I created a indexer with type list for Flight, I also create a setter for it. In the main I tried to set value for the list but keep receive exception when running the code.

This is my class Flight:

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

namespace Assignment3
{
    class Flight
    {
        private int id;
        public int Id
        {
            get { return id; }
            set {  this.id = value; }
        }

        private string origin;
        public string Origin
        {
            get { return origin; }
            set { this.origin = value; }
        }

        private string destination;
        public string Destination
        {
            get { return destination; }
            set { this.destination = value; }
        }

        private string date;
        public string Date
        {
            get { return date; }
            set { this.date = value; }
        }

        private double price;
        public double Price
        {
            get { return price; }
            set { this.price = value; }
        }

        public Flight(int id, string origin, string destination, string date, double price) {
            this.id = id;
            this.origin = origin;
            this.destination = destination;
            this.date = date;
            this.price = price;
        }

        public bool FindFlight(int searchId)
        {
            if(searchId == this.id)
            {
                return true;
            }
            return false;
        }
        public override string ToString()
        {
            string s = "Flight ID: " + id + "\nOrigin: " + origin + "\nDestination: " + destination +
                        "\nDate: " + date + "\nPrice: " + price + "$";
            return s;
        }
    }
}

This is my AirlineCompany class:

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

namespace Assignment3
{
    class AirlineCompany
    {
        public static readonly string airlineName;
        static AirlineCompany()
        {
            airlineName = "Vietjet airline";
        }
        public List<Flight> flights= new List<Flight>(100);
        public Flight this[int index]
        {
            set
            {
                flights.Insert(index, value);
            }
            get
            {
                return flights[index];
            }
        }
    }
}

This is my main class:

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

namespace Assignment3
{
    class Program
    {
        static void Main(string[] args)
        {
            AirlineCompany vn = new AirlineCompany();
            Console.WriteLine(AirlineCompany.airlineName);
            vn.flights[0] = new Flight(1,"Viet Nam","Finland","24/11",169.9);
            vn.flights[1] = new Flight(2, "Finland", "Singapore", "25/11", 109.9);
            vn.flights[2] = new Flight(3, "Singapore", "Finland", "26/11", 129.9);
            vn.flights[3] = new Flight(4, "Holland", "Germany", "27/11", 69.9);
            Console.ReadLine();
        }
    }
}

This is the exception when I run code:

Answer 1

The int constructor argument of a List<T> e.g new List<Flight>(100) isn't its initial size, it's the Capacity.

Gets or sets the total number of elements the internal data structure can hold without resizing.

I.e. the pre-allocated internal backing array size.

Secondly, you are not using the Indexer you are using the member List property, you might as well just use the List for what it is

vn.flights.Add(new Flight(1,"Viet Nam","Finland","24/11",169.9));

If you wanted to use the Indexer, you would use the following syntax

vn[0] = new Flight(1,"Viet Nam","Finland","24/11",169.9);

However this is going to get you into all sorts of trouble fairly quickly, you would actually need to initialize the list with the appropriate size first (like you originally set out to do).

public List<Flight> flights= new List<Flight>(new Flight[100]);

In which case, why would you want this to be a list and not just an array?

public Flight[] flights = new Flight[100];

In short, an indexer seems like the wrong tool for the job here.

Though, if you really wanted to use it, it seems more normal just to proxy the call to the indexer of the list / array.

public Flight this[int index]
{
   set => flights[index] = value;
   get => flights[index];
}

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Further reading

Indexers (C# Programming Guide)