Announcements
• Let’s reflect on the course: How are you doing? • Let me know in the survey!
• HW4 is posted! This is the beginning of the spreadsheet application – have fun!J
Spreadsheet Application Design Overview
Cpt S 321 Washington State University
Recall: Decouple Logic/Data and UI
UI
Engine (Data/Logic)
Spreadsheet Design
UI (WinForms app)
Engine (class library)
The spreadsheet solution consists of a WinForms project for UI and a DLL class library project for the engine
Spreadsheet Design
Cell class
Spreadsheet class
Inside the logic engine are classes for Cell and Spreadsheet.
UI
Spreadsheet Design
Cell class
Spreadsheet class
UI
Changes in the Spreadsheet will bubble-up to the UI through property-change notifications. UI will update appropriately.
Follow the Model-View Separation Principle
• States that: Model (domain) objects should not have direct
knowledge of view (UI) objects.
• Thus in the Spreadsheet application the Cell and Spreadsheet classes will not directly reference neither send messages to the WinForm class.
• Also, the WinForm class will not contain any logic (such as formula calculation). UI objects should only initialize UI elements, receive UI events (such as a mouse click on a button), and delegate requests for application logic on to non-UI objects (such as domain objects).
Spreadsheet Design (Engine)
• Cell class: members
• Text (public string property)
• Represents the exact text that was entered into the cell. • Value (public string property)
• Represents the evaluated value of the cell. If the cell has a formula this will be the result of computing that formula. Otherwise it has the same value as the Text property (hence the string type)
• Read-only to the world outside of the Spreadsheet class (Why?)
• (more properties will come later with the introduction of new features)
Spreadsheet Design (Engine)
• Cell class: purpose
• Store the text and value for a single cell
• Protect Value property from being set by anything other than the Spreadsheet class
• You will need to figure out how to use C# language features to achieve this on the homework
• Provide the ability to notify of property changes
• Cell class will implement INotifyPropertyChanged interface • When Text or Value changes, invoke notification event
Spreadsheet Design (Engine)
• Spreadsheet class: members
• Cell GetCell(int columnIndex, int rowIndex)
• Member function to the cell at the specified column and row indices • Indices are zero-based
• Cell GetCell(string cellName)
• Member function to get a cell by name (e.g. “A1”)
• Can be implemented by parsing the string and calling the other overload
Spreadsheet Design (Engine)
• Spreadsheet class: purpose
• Store the 2D array of cells in the spreadsheet
• Allow observers to subscribe to change events and provide notifications of any change in the spreadsheet
• Subscribe to change events in all internally managed cells
• When they change, forward the event to observers of the spreadsheet CellPropertyChanged event
Important: Follow Good Design Principles/Patterns!
• Follow the Model-View Separation Principle
• Promote encapsulation (i.e., set the proper access modifiers to your
entities)
• Use all principles/patterns that
1. Apply for the current HW and
2. we have seen in class
General Responsibility Assignment Software Patterns/Principles: GRASP
• Guidelines for assigning responsibility to classes and objects in object- oriented design
• Guided by one main question “Whose responsibility is it?”
• Nine principles and we are already familiar with some of them:
• Information Expert: Assign the right responsibilities to the right entities (i.e., to the right classes, methods, etc.).
Problem: What is a basic principle by which to assign responsibilities to objects?
• Solution: Assign a responsibility to the class that has the information needed to fulfill it.
GRASP (cont.)
• Low Coupling
• Problem: How to reduce the impact of change?
• Solution: Assign responsibilities so that (unnecessary) coupling remains low. Use this principle to evaluate alternatives.
• High Cohesion
• Problem: How to keep objects focused, understandable, and manageable, and as
• Solution: Assign responsibilities so that cohesion remains high. Use this to evaluate alternatives.
• Polymorphism
• Problem: How handle alternatives based on type?
• Solution: When related alternatives or behaviors vary by type, assign responsibility for the behavior using polymorphic operations to the types for which the behavior varies (instead of explicit branching based on type).
a side effect, support Low Coupling?