General requirements:

• You will need to follow the style laid out in the C# Coding Conventions

• Implement functionality for a creating and updating an order

Assignment requirements:

• Implement a base class or interface to provide a common type for all of your menu items

• Implement a class Order representing an order

• Write unit tests for the Order class

• Add the functionality for creating, updating, and displaying the order in the Point of Sale GUI

• Create automated tests for your GUI

• Update UML Diagrams

Purpose:

This assignment is intended to help you gain a greater grasp of creating complex objects and collections, data binding, customizing controls, and more complex relationships between objects. It also revisits testing in the context of GUI applications.

A Common Type for your Menu Items

An order needs to hold all kinds of items - drinks, entrees, sides, etc. To put all of those different types into a collection, ideally they will share a common type. That could be done through an interface they all inherit (i.e. IMenuItem) or a common base class (MenuItem). You can choose which strategy you prefer, but you need to write one of these, and make sure that all of your menu items can be treated as it.

You’ll also want to have that base class or interface define all the properties that all menu items have in common; namely a Name, Price, and Calories. You’ll also want to add a new property, SpecialInstructions, of type ICollection<String> (this can be satisfied by a List<string> or string[]) that will be used to indicate when a change from the normal way of preparing the menu item has been asked for. For example, if a PrehistoricPBJ is ordered without peanut butter, it should contain “Hold Peanut Butter”. If a AllosaurusAllAmerican is ordered with american cheese and bacon, it should contain “Add American Cheese” and “Add Bacon”.

You will need to refactor your menu item classes to support these additional requirements, and add the corresponding unit tests.

Implement functionality for the Order class

In the Data project, create an Order class to represent an order, which is a collection of IMenuItems. You will need to create public Add(IMenuItem item) and Remove(IMenuItem item) methods, which add or remove IMenuItems respectively. Additionally, you should implement a getter and setter for SalesTaxRate (a decimal, default 0.09) and getter-only properties for Subtotal (a decimal), Tax (a decimal), and Total (a decimal). The Subtotal is the total price for all items in the order, the Tax is the Subtotal multiplied by the SalesTaxRate, and Total is the sum of the Subtotal and Tax. It should also provide a property Calories which is a unsigned integer, and the sum of all the calories of the items in the order.

Additionally, the Order should have an identifying Number getter property, which is unique to each order. An easy way to ensure uniqueness is to have a private static field, i.e. nextOrderNumber, which is initialized to 1. In the Order constructor, set this order’s Number property to nextOrderNumber and then increment nextOrderNumber. When your next order is created, it will use the incremented value, and increment it again. Technically this only ensures a single Point of Sale terminal is using unique order numbers (as multiple terminals will have duplicate values), but it is sufficient for now.

Also, the Order should have a get-only DateTime property PlacedAt identifying the date and time the order was placed.

Finally, this class should implement the ICollection, INotifyCollectionChanged, and INotifyPropertyChanged interfaces. Each of these requires you to add specific properties and methods to the Order class. This also means triggering a host of events when specific actions are taken, i.e.:

• Adding an IMenuItem to the Order should trigger:
  1. A CollectionChanged event noting the addition of a new item
  2. A PropertyChanged event noting the Subtotal property has changed
  3. A PropertyChanged event noting the Tax property has changed
  4. A PropertyChanged event noting the Total property has changed
  5. A PropertyChanged event noting the Calories property has changed
• Removing an IMenuItem from the Order should trigger:
  1. A CollectionChanged event noting the removal of the item
  2. A PropertyChanged event noting the Subtotal property has changed
  3. A PropertyChanged event noting the Tax property has changed
  4. A PropertyChanged event noting the Total property has changed
  5. A PropertyChanged event noting the Calories property has changed
• Changing an item already in the order should trigger:
  1. PropertyChanged events for Subtotal, Tax, and Total when the item’s Price changes
  2. A PropertyChanged event for Calories when the item’s Calories changes

You may either write your collection class from scratch, use a private collection field and expose some of its methods through pass-through methods, or inherit from one of the existing collections and provide the extra functionality (such as ObservableCollection). Each of these approaches has its strengths and drawbacks.

  private List<IMenuItem> _items = new List<IMenuItem>();

  public IEnumerator<IMenuItem> GetEnumerator()
  {
    return _items.GetEnumerator();
  }

Order Unit Tests

Additionally, you should write unit tests to verify all of the expected functionality:

• Adding an item to the Order results in that item being included in the order
• Removing an item from the Order results in that item being removed from the order
• The order implements the INotifyCollectionChanged and INotifyPropertyChanged interfaces
• That adding an an item triggers a CollectionChanged event
• That removing an item triggers a CollectionChanged event
• That and that each of the CollectionChanged and PropertyChanged events described above occur in the described circumstances.

Integrate the Order into the Point of Sale Project

The Point of Sale GUI’s primary role is to build Order objects to match the customers’ requests. Thus, you will want to integrate your new Order class into the GUI to provide this functionality. The easiest way to accomplish this is to set your Order as the DataContext of one of your WPF elements - ideally towards the top of the tree. Then, all of the descendant elements will also have it as their DataContext.

You should replace this Order object any time the “New Order” or “Cancel Order” button (depending on your implementation) are clicked.

Clicking on one of the “Add to Order” buttons you implemented should add an instance of the associated order item to the current Order object.

The contents of the current Order should be displayed prominently in your GUI, for example, by using a <ListView>. You will want to display:

• The Menu Item’s name
• The Menu Item’s price
• The Menu Item’s special instructions

Hint: You can add a StringFormat attribute to a binding to display it as currency, i.e.: <TextBlock Text={Binding Path=Total, StringFormat={}{0:c}}>. This approach can also be used to add bullets or extra text to a bound string before it is displayed. See the docs for more details.

In addition, you will need to show:

• The Order’s Number property, formatted for readability, i.e. “Order #2”
• The Order’s PlacedDate property, formatted for readability, i.e. “3/20/2021 10:32 pm”
• The Order’s Subtotal property, formatted for readability, i.e. “Subtotal: $10.00”
• The Order’s Tax property, formatted for readability, i.e. “Tax: $1.20”
• The Order’s Total property, formatted for readability, i.e. “Total: $11.20”

One possible layout appears below:

The displayed order should update all of this displayed information as it changes. If you use data binding for binding the Order properties, and have implemented the CollectionChanged and PropertyChanged events as described above, this should happen automatically, with no further code required from you.

You should also allow the user to select an item already in the order display to customize, i.e. if they have a Prehistoric PB&J and a Cretaceous Coffee in the Order, and then need to change the PeanutButter property for the PrehistoricPBJ instance, they should be able to do so. There several approaches you might consider:

1. Putting the order items in a <ListView> and using its OnSelectionChanged event to swap to the customization screen. You can then either: a. Listen for the ListView.SelectionChanged routed event and use the SelectedChangedEventArgs.SelectedItem for the item to customize, or b. Setting the List’s IsSynchronizedWithCurrentItem property to true allows you to bind your customization screens to the CurrentItem Path of the Order, i.e. the item just selected in the <ListView>, or
2. Adding an edit button to the item in the <ListView>, following the same strategy detailed for the “Remove” button (below)

Finally, you should provide a means for removing an item from the Order. This is most commonly accomplished by adding a button to the ListBoxItem data template displaying the items in the <ListBox>, so that there is a delete button for each row in the order. Another approach would be to have a single “Remove Selected Item from Order” which removes the item currently selected in the <ListBox>. A third approach would be to put a “Remove from Order” button in the customization screen, that when clicked removes the item from the order an switches back to the menu item selection screen. Other approaches are possible, but should be easy for the user to intuit.

Update Your UML Diagrams

You will need to update your UML diagrams to reflect the changes you have made to the Data and Point of Sale projects. Remember to mark the associations between your Order and its various Menu Item instances.

Submitting the Assignment

Once your project is complete create a release tagged v0.7.0 with name "Milestone 7". Copy the URL for the release page and submit it to the Canvas assignment.

Grading Rubric

The grading rubric for this assignment will be:

15% Structure Did you implement the structure as laid out in the specification? Are the correct names used for classes, enums, properties, methods, events, etc? Do classes inherit from expected base classes?

15% Documentation Does every class, method, property, and field use the correct XML-style documentation? Does every XML comment tag contain explanatory text?

15% Design Are you appropriately using C# to create reasonably efficient, secure, and usable software? Does your code contain bugs that will cause issues at runtime?

15% UML Diagrams Does your UML diagram reflect the code actually in your release? Are all classes, enums, etc. included? Are associations correctly identified?

20% Functionality Does the program do what the assignment asks? Do properties return the expected values? Do methods perform the expected actions?

20% Testing Do you have unit tests for all classes? Do your unit tests cover all the functionality of those classes?