Open the project and review the code

$1.$Open the InventoryMaintenance project. This is an enhanced version of the Inventory Maintenance application from module six that uses a list class.

InventoryMaintenance $(5).$zipDownload InventoryMaintenance $(5).$zip

$2.$Review the code for the InvItemList class so you understand how it works. Then, review the code for the Inventory Maintenance form to see how it uses this class. Finally, run the application to see how it works.

$$

Add an index to the InvItemList class

$3.$Delete the GetItemByIndex method from the InvItemList class, and replace it with an indexer that receives an int value. This indexer should include both get and set accessors, and the get accessor should check that the value that$$s passed to it is a valid index. If the index isn$$t valid, the accessor should throw an ArgumentOutOfRangeException with a message that consists of the index value.

$4.$Modify the Invoice Maintenance form to use this indexer instead of the GetItemByIndex method. Then, test the application to be sure it still works.

$$

Add overloaded operators to the InvItemList class

$5.$Add overloaded $+$ and $-$ operators to the InvItemList class that add and remove an inventory item from the inventory item list.

$6.$Modify the Inventory Maintenance form to use these operators instead of the Add and Remove methods. Then, test the application to be sure it still works.

Add a delegate and an event to the InvItemList class

$7.$Add a delegate named ChangeHandler to the InvItemList class. This delegate should specify a method with a void return type and an InvItemList parameter.

$8.$Add an event named Changed to the InvItemList class. This event should use the ChangeHandler delegate and should be raised any time the inventory item list changes.

$9.$Modify the Inventory Maintenance form to use the Changed event to save the inventory items and refresh the list box any time the list changes. To do that, you$$ll need to code an event handler that has the signature specified by the delegate, you$$ll need to wire the event to the event handler, and you$$ll need to remove any unnecessary code from the event handlers for the Save and Delete buttons. When you$$re done, test the application to be sure it still works. Take a screenshot.

The code I$\text{'}$m working with below

invitemlist.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace InventoryMaintenance

$\{$

public class InvItemList

$\{$

private List invItems;

public InvItemList$()$

$\{$

invItems $=$ new List$()$;

$\}$

public int Count $=>$ invItems.Count;

public InvItem GetItemByIndex$($int i$)=>$ invItems$[$i$]$;

public void Add$($InvItem invItem$)=>$ invItems.Add$($invItem$)$;

public void Add$($int itemNo, string description, decimal price$)$

$\{$

InvItem i $=$ new InvItem$($itemNo$,$ description, price$)$;

invItems.Add$($i$)$;

$\}$

public void Remove$($InvItem invItem$)=>$ invItems.Remove$($invItem$)$;

public void Fill$()=>$ invItems $=$ InvItemDB.GetItems$()$;

public void Save$()=>$ InvItemDB.SaveItems$($invItems$)$;

$\}$

$\}$

frminvmaint.cs

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;

namespace InventoryMaintenance

$\{$

public partial class frmInvMaint : Form

$\{$

public frmInvMaint$()$

$\{$

InitializeComponent$()$;

$\}$

private InvItemList invItems $=$ new InvItemList$()$;

private void frmInvMaint$\_$Load$($object sender$,$ EventArgs e$)$

$\{$

invItems.Fill$()$;

FillItemListBox$()$;

$\}$

private void FillItemListBox$()$

$\{$

InvItem item;

lstItems.Items.Clear$()$;

for $($int i $=0$; i $<$ invItems.Count; i$++)$

$\{$

item $=$ invItems.GetItemByIndex$($i$)$;

lstItems.Items.Add$($item$.$GetDisplayText$())$;

$\}$

$\}$

private void btnAdd$\_$Click$($object sender$,$ EventArgs e$)$

$\{$

frmNewItem newItemForm $=$ new frmNewItem$()$;

InvItem invItem $=$ newItemForm.GetNewItem$()$;

if $($invItem $!=$ null$)$

$\{$

invItems.Add$($invItem$)$;

invItems.Save$()$;

FillItemListBox$()$;

$\}$

$\}$

private void btnDelete$\_$Click$($object sender$,$ EventArgs e$)$

$\{$

int i $=$ lstItems.SelectedIndex;

if $($i $!=-1)$

$\{$

InvItem invItem $=$ invItems.GetItemByIndex$($i$)$;

string message $=$ "Are you sure you want to delete $"$

$+$ invItem.Description $+"?"$;

DialogResult button $=$

MessageBox.Show$($message$,$ "Confirm Delete",

MessageBoxButtons.YesNo$)$;

if $($button $==$ DialogResult.Yes$)$

$\{$

invItems.Remove$($invItem$)$;

invItems.Save$()$;

FillItemListBox$()$;

$\}$

$\}$

$\}$

private void btnExit$\_$Click$($object sender$,$ EventArgs e$)$

$\{$

this.Close$()$;

$\}$

$\}$

$\}$