Please Answer In C#$.$ Extra $15-1$ Create and use an interface

In this exercise, you'll create an IDisplayable interface and then use it in the

InventoryItem class of the Inventory Maintenance app.

$1.$Open the InventoryMaintenance project in the ExtraStarts Chp $15$

InventoryMaintIDisplayable directory.

$2.$Create a public interface named IDisplayable. Then, add the declaration for a

method named GetDisplayText$()$ with no parameters and a string return value.

$3.$Display the code for the InventoryItem class, find the GetDisplayText$()$ method

that this class contains, and comment out this method.

$4.$Modify the declaration for the class to indicate that it implements the

IDisplayable interface. Then, generate a stub for the GetDisplayText$()$ method

that this interface defines.

$5.$Modify the declaration for the GetDisplayText$()$ method so it can be overridden.

Then, replace the generated code for this method with the code in the original

GetDisplayText$()$ method that you commented out in step $3.$

$6.$Test the app to be sure it still works.

$7.$Display the code for the Inventory Maintenance form. In the FillItemListBox$()$

method, change the type of the item variable from InventoryItem to IDisplayable.

$8.$Test the app to be sure it still works.

$9.$Modify the event handler for the Click event of the Add button to include the

following debugging code after the code that gets an InventoryItem object named

item from the New Item form:

Debug.Writeline $($$"Item type: $\{$item$.$GetType $()\}")$;

Debug.WriteLine$($$"Item is InventoryItem: $\{$item is InventoryItem$\}")$;

Debug.WriteLine$($$"Item is IDisplayable: $\{$item is IDisplayable$\}")$;

$10.$ Run the app and add a new Plant item and a new Supply item. After adding each item, check the Output window and review the information that's displayed. Here is the code I have so far starting with the main page $,$ then including the Inventory item class. using System.Diagnostics;

namespace InventoryMaintenance

$\{$

public partial class frmInventoryMaint : Form

$\{$

public frmInventoryMaint$()$

$\{$

InitializeComponent$()$;

$\}$

private InventoryItemList items $=$ new$()$;

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

$\{$

items.Changed $+=$ new InventoryItemList.ChangeHandler$($HandleChange$)$;

items.Fill$()$;

FillItemListBox$()$;

$\}$

private void FillItemListBox$()$

$\{$

IDisplayable item $=$GetSelectedItem$()$;

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

lstItems.Items.Clear$()$;

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

$\{$

item $=$ items$[$i$]$;

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

$\}$

$\}$

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

$\{$

IDisplayable item $=$ GetNewItem$()$;

frmNewItem newItemForm $=$ new$()$;

InventoryItem item $=$ newItemForm.GetNewItem$()$;

if $($item $!=$ null$)$

$\{$

items $+=$ item;

$\}$

Debug.WriteLine$($$"Item type: $\{$item$.$GetType$()\}")$;

Debug.WriteLine$($$"Item is InventoryItem: $\{$item is InventoryItem$\}")$;

Debug.WriteLine$($$"Item is IDisplayable: $\{$item is IDisplayable$\}")$;

$\}$

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

$\{$

int i $=$ lstItems.SelectedIndex;

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

$\{$

MessageBox.Show$("$Please select an item to delete.", $"$No item selected"$)$;

$\}$

else

$\{$

InventoryItem item $=$ items$[$i$]$;

string message $=$ $"Are you sure you want to delete $\{$item$.$Description$\}?"$;

DialogResult result $=$

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

MessageBoxButtons.YesNo$)$;

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

$\{$

items $-=$ item;

$\}$

$\}$

$\}$

private void HandleChange$($InventoryItemList invItems$)$

$\{$

invItems.Save$()$;

FillItemListBox$()$;

$\}$

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

$\{$

this.Close$()$;

$\}$

$\}$

$\}//$ now the inventory item class using System.Reflection.Metadata.Ecma$335$;

namespace InventoryMaintenance

$\{$

public class InventoryItem : IDisplayable

$\{$

public InventoryItem$()\{\}$

public InventoryItem$($int itemNo, string description, decimal price$)$

$\{$

ItemNo $=$ itemNo;

Description $=$ description;

Price $=$ price;

$\}$

public int ItemNo $\{$ get; set; $\}$

public string Description $\{$ get; set; $\}=""$;

public decimal Price $\{$ get; set; $\}$

public virtual string GetDisplayText$()=>$ $$"\{$ItemNo$\}\{$Description$\}(\{$Price:c$\})"$;

$//$ public virtual string GetDisplayText$()$

$//\{$

$//$ return "Display text for inventory item"; $\}$