1. GUI and systems Presentation and models Views and presentation logic
GUI Architectures
GUI and systems
Presentation and models
Views and presentation logic

2. GUI Architectures GUI and systems Presentation and models
Views and presentation logic
XP: eXtreme Programming, Kent Beck et al
DSDM: Dynamic System Development Method, DSDM Consortium, UK
Crystal: Crystal Clear and other Crystal methods by Alistair Cockburn
Evo: Evolutionary development, Tom Gilb
FDD: Feature Driven Development, Jeff De Luca
Lean: Lean Software Development, Mary and Tom Poppendieck 2

3. Visual Interfaces and Application Logic
Yes,
with a widget-based system
it is easy to avoid having to think about the (required) separation
between the user interface
and the application domain objects,
but it is all too easy to allow
one’s domain code
to become inextricably linked with
the general interface logic.
From Dolphin Smalltalk design report
[TWISTING THE TRIAD] Design paper for Dolphin Smalltalk, 2000

4. How to Select an Application Architecture
Caching? State?
Users
Focus
UI Components 1
Presentation Layer
UI Process Components 2
”Interface logic”
Communication
Operational Management
Security
Service Interfaces
”Domain code”
Business Services Layer
Business Workflows
Business Components
Business Entities
Data Access Logic Components
Service Agents
Additional Services Layer
Data Layer
Data Sources
Services
[MSF], Microsoft Solution Framework, [MSPnP] patterns & practices: Architecture

5. Integrated Logic
Let us make a quick booking solution WizardForm with a BookingForms
Using the Visual Studio Design Wizard
Including direct access to the database
Generated code for saving a new booking
private void bookingBindingNavigatorSaveItem_Click (object sender, EventArgs e) {
this.Validate();
this.bookingBindingSource.EndEdit();
this.tableAdapterManager.UpdateAll(this.rBSDataSet); }

6. The Elements of the Integrated Program
Visual Studio creates a binding source-object
Acts as a data source for navigation bar and data grid
level of indirection with a uniform protocol
May be bound to different kinds of data sources
Is an adapter between the data clients and the data source
The binding source gets its data from the dataset
An off-line representation of part of the database
A table adapter synchronizes the dataset with the database
Fills the dataset and updates the database
Small group discussion
Identify the layers of this solution on the reengineered structure at the next slide
With permission from ProgramUtvikling as 6

7. Reengineering the Integrated Program
:RoomsForm
:RBSDataSet
:BindingSource
roomsBindingNavigator :
BindingNavigator
:RoomsTableAdapter
roomsDataGridView :
DataGridView
:Program
«table»
:Rooms
-roomsTableAdapter
-roomsBindingSource
«use»
«launch»
+DataSource
+BindingSource
-rBSDataSet
-event handler 7

8. Study the Application Logic
Identify the responsibilities of each layer
The presentation layer
Knows how to present, receive and navigate through data
The data source layer
Knows how to make data available to the presentation layer
Keeps track of which data have been removed, added or changed
Knows how to move data between the data source and the off-line data representation
There is no domain logic in this application
Information about the rules for using the data
It is with the user alone 8

9. Add some Domain Logic Add data validation
Entered number of seats cannot be negative
Class Discussion: Evaluate alternative strategies
Add constraint to the database
CK_SeatsNonNegative: ([Seats]>=(0))
Discussion:
Add constraint to the dataset
Add validation code run during data input
Event handling for cell value changed 9

10. Some Possible Considerations
Add constraint to the database
Can not be validated before data is saved
Signalled by throwing an exception
Must be caught and handled in the application
Add constraint or validation to the record set
Unique constraints and foreign-key constraints are readily available
OnColumnChanging event handler may add further validation
Requires manual programming
Record set will have domain validation
Add validation code run during data input
Makes immediate validation possible
Data grid will have domain validation
Where to locate that code? 10

11. Rudimentary Data Validation for Number of Seats
Event handling for cell value change
Located in RoomsForm
private void roomsDataGridView_CellValueChanged(
object sender, DataGridViewCellEventArgs e) {
DataGridView senderView = (DataGridView)sender;
if (e.RowIndex >= 0) // Only validate data cells
switch (senderView.Columns[e.ColumnIndex].HeaderText)
case "Seats":
ValidateSeats(senderView, e.RowIndex, e.ColumnIndex);
break;
} // switch HeaderText
} // rowIndex >= 0 } 11

12. A Support Function to do the Validation
/// <summary>
/// Validate data entry for the Seats property
/// <pre>Pre: The current cell is a Seats data cell</pre>
/// <post>Post: If the current value is valid, nothing has happened, else
/// the user has been notified and the cell has been restored to its
/// previous value</post>
/// </summary>
private void ValidateSeats(DataGridView sender, int row, int column) {
object valueObject = sender.Rows[row].Cells[column].Value;
if (valueObject != null
&& valueObject.GetType() != typeof(System.DBNull))
int value = (int)valueObject;
if (!(value >= 0))
MessageBox.Show("Invalid value: " + value);
sender.Rows[row].Cells[column].Value = currentValue; }
} // has a value
} // ValidateSeats 12

13. Architecture and Dependencies
Presentation Layer
Input Controller
View
MessageBox
SaveItem_Click
Binding Navigator
CellEnter
Data Grid View
CellValueChanged
Rooms Form
Load
Binding Source
FormClosing
Domain Layer
Model
ValidateDirty
Dirty
Validate Seats
Save
Data Source Layer
Data Source Logic
TableAdapter
Record Set 13

14. Architecture and Dependencies
Presentation Layer
Input Controller
View
MessageBox
SaveItem_Click
Binding Navigator
CellEnter
Data Grid View
CellValueChanged
Rooms Form
Load
Binding Source
FormClosing
Domain Layer
Model
ValidateDirty
Dirty
Validate Seats
Save
Data Source Layer
Data Source Logic
TableAdapter
Record Set 14

15. GUI Architectures GUI and systems Presentation and models
Views and presentation logic
XP: eXtreme Programming, Kent Beck et al
DSDM: Dynamic System Development Method, DSDM Consortium, UK
Crystal: Crystal Clear and other Crystal methods by Alistair Cockburn
Evo: Evolutionary development, Tom Gilb
FDD: Feature Driven Development, Jeff De Luca
Lean: Lean Software Development, Mary and Tom Poppendieck 15

16. Transaction Script Integrates All Logic
Search and display
Modify, save, display
Presentation and presentation Logic
Application Logic 16

17. A Solution with an Object Model
Example code to insert a booking
private void AddButton_Click(object sender, EventArgs e) {
Booking candidate = MakeNewBooking();
if (BookingValidation.IsValid(candidate))
Mapper.BookingMapper.Add(candidate);
LoadData();
LocateAt(candidate); }
else
MessageBox.Show("Illegal booking data entered");

18. Presentation is Supported by Domain
Run application and make a booking
Input event is caught by an event handler
Does some validation
Supported by domain objects
Calls domain objects to do some operation
Displays result
Similar to a pure update (next slide)
Design principle: Separate Presentation
Information flow: Flow Synchronization
The form knows who needs the information

19. Query Example: Get Available Rooms
For queries / accessors (no change) or one single view
Transfer result to View Logics
From time:
Fossekallen –12.00
Setesdal –15.00
Fossekallen –17.00
To time:
Search
5 display list
1: click event
2: get data
4 DisplayAvailable(rooms)
: Input Controller
: View or Presenter
Presentation logic
Domain logic
3 rooms = GetAvailable(from, to)
: BookingFinder
= model in MVC terms 19

20. A More Elaborate Example
Run application with several windows displaying overlapping information
You want a change in one of the windows to appear in the others
Design principle: Separate Presentation
Information flow: Observer Synchronization
Design pattern: Observer
.NET implementation: Events
Implicitly handled by data binding

21. Command Example: Reserve a Room
For commands / transformers (change) and more than one view
View subscribes to Service Layer events
Notification is implicit through events (Separate Presentation)
Room:
Fossekallen
Fossekallen –12.00
Setesdal –15.00
Fossekallen –17.00
From time:
Controls
To time:
Reserve
1: click event
6 display list
2: get data
: Input Controller
: View Logic
Form class
4 change event
5 get display info
3 ReserveRoom(room, from, to)
Presentation layer
= model in MVC terms
Domain layer
: Booking 21

22. Subscribing To and Handling Events
Observer
Subscribes to (or is subscribed to) the event and does initial update
Receives events to handle incremental update 1 2

23. Implementing Observers in C#
Part 1: Initialization – Define and subscribe to the event
Model (class Booking) declares an event
public event System.EventHandler ParticipantsChanged;
Observer client supplies a model to the observer
RBS: new BookingForm(booking).Show();
BookingForm: new AddParticipantForm(booking).Show();
Observers define event handler for incremental event handling
BookingForm, AddParticipantsForm
private void booking_ParticipantsChanged( object source, System.EventArgs args) {...}
Observers subscribe to the event (in constructor or set Model property)
booking.ParticipantsChanged += new EventHandler(booking_ParticipantsChanged);
Observers perform initial update from model
Part 2: Update – Model triggers and observer receives event
Model (class Booking) fires event (e.g. in AddParticipants)
ParticipantsChanged(this, new System.EventArgs());
Causes observer (BookingForm, AddParticipantsForm) event handler to be called
booking_ParticipantsChanged(object source, System.EventArgs args);
When debriefing the exercise, point out:
1.1 We use the built-in System.EventHandler as event type
1.2 Event handler parameters are defined by the event, method name is system convention
1.3 In BookingForm and AddParticipantsForm, connecting to model is isolated as separate property BindingSource, called from constructor 23

24. Adding Another UI Device
You want to allow room booking over the web
Display a simple demo of ASP.NET server side application logic
A data grid bound to Booking objects
Through BookingMapper
Don’t forget to initialize the MapperFactory singleton
Four separate fields and a button implement booking functionality
Web application is supported by same domain logic as before
Thanks to Separate Presentation

25. A Web Session
server
client 25

26. One Page Life Cycle
server
client 26

27. Handling ASP.NET Page Life Cycle Events
A page raises events for each stage of its life cycle
Can be handled in your own code
Bind the event handler to the event
Declaratively using attributes such as onclick
In code
Pages also support auto event wire-up
ASP.NET looks for methods with particular names
Automatically runs those methods when certain events are raised
Requires Page AutoEventWireup="true" %>
Naming convention Page_event
Page_Load, Page_Init
Or if AutoEventWireup is not defined, since the default value is true. 27

28. Web Servers are Stateless
The HTTP protocol does not relate subsequent Web requests to each other
The request following mine may come from a completely unrelated browser
The server must establish the connection between related requests
By storing an identification at the client side
This identifies a session from one browser
Two main strategies for recognizing a session identity
Server stores an id with the client and asks for it each time
Cookies
Server includes an id in the Web page, returned with the next request
Hidden field
A parameter in the URL 28

29. Strategies for Storing Session State
Once the session is identified
The session state data may be retrieved
Different data storage techniques
Session State
Session identifier identifies a state object in server memory
Contains all the session variables
View State
Session data sent between server and client with each view
Persistent State
Session variables stored on disk
Search key = session identifier 29

30. Fully Dressed Class Structure30

31. Working with Session Data
ASP.NET Session data object is only accessible through a Web page
Encapsulate session data in a typed class
Declared separately
internal class TypedSession { private HttpSessionState session; public TypedSession() {session = System.Web.HttpContext.Current.Session;} public string UserId{ get { return (string)session[”UserId”]; } set { session[”UserId”] = value; } } ... more session variables ... }
Used from a Web page or layer supertype object, initialised in Page_Load
private TypedSession Session = new TypedSession();
: Used to be
private TypedSession session = new TypedSession(this);
protected TypedSession Session {get {return session;} }
Unfortunately,there is a bug in VS2005, so the expression
Session.UserId = “Eivind” gets a compiler error, saying that Session cannot be assigned to sinc it is not a variable. That is true, but it if wrong that this expression tries to assign it a value. This needs to be looked closer into.
Reference to System.Web.dll required 31

32. Delegate Event Handling to Input Controller
Getting hold of an input controller
Suggest an implementation of the Controller property 32

33. Getting Hold of a Controller
One implementation of the Controller property
In the code-behind class
Implement the controller as a local ”singleton”
The controller may have to call back for properties or commands
private MyInputController controller;
protected MyInputController Controller { get { if (controller == null){ controller = new MyInputController(this); } return controller; } } 33

34. Initial Page-Load Event Handling
Initial loading of a page is done signalled in Page_Load event handler
if (!IsPostback){ Controller.HandleRequestParameters(parameters); this.LoadFormData(); }
The diagram only shows the Page_Load part of the page life cycle 34

35. GUI Architectures GUI and systems Presentation and models
Views and presentation logic
XP: eXtreme Programming, Kent Beck et al
DSDM: Dynamic System Development Method, DSDM Consortium, UK
Crystal: Crystal Clear and other Crystal methods by Alistair Cockburn
Evo: Evolutionary development, Tom Gilb
FDD: Feature Driven Development, Jeff De Luca
Lean: Lean Software Development, Mary and Tom Poppendieck 35

36. Validation code From WinForm solution
Booking candidate = MakeBooking();
if (BookingValidation.IsValid(candidate)) {
Mapper.BookingMapper.Add(candidate);
LoadData();
LocateAt(candidate); }
else
MessageBox.Show("Illegal booking data entered");

37. Validation Code From WebForm solution
Booking candidate = MakeNewBooking();
if (IsBookingValid(candidate)) {
Add(candidate);
Response.Redirect("BookingsForm.aspx"); }
else
Response.Write("<P>Den nya beställningen är inte giltig</P>");

38. The Input Handling is The Same
There is code duplication between the two
Symptom of wrong location
Separate common code in a separate input controller class
Delegate from event handler to input controller
Supply the information needed by the controller
Some of the functions may be pushed all the way to the domain logic
Similar situations occur on output
Separate out common presentation aspects in a presenter
Presenter must talk with the form
The form is dumb
Input controller and presenter may be developed using TDD
May be combined into one Input Controller/Presenter

39. Communication Scenario for MVC
2: AddBooking
7: if (alarm) SetColor(red)
1: NewBooking
3: BookingAddedEvent
4: GetBookings
5: ShowBookings
6: alarm = IsAlarm
: Form 5
, 7 1
: Input Controller
: Presenter 3 2 4
, 6
: Domain Logic
= model in MVC terms 39

40. Issues for Different Output Devices
The controller and presenter do the same job for both windows and web
Talk to the form through an interface
Or use an adapter in-between
Requires all output operations in the form to be formalised
SetBookingList(bookings)
instead of BookingDataGrid.DataSource = bookings
Defined in the interface
Implemented in each of the forms or the adapter
The forms may be replaced by dummy classes for testing
The whole application is tested except physical input and display

41. Exercise 6.2 – Web Presentation Architecture
: Page
2: AddBooking
1: NewBooking
3: BookingAddedEvent
4: GetBookings
6: alarm = IsAlarm
5: ShowBookings
7: if (alarm) SetColor(red) or
: Form 1 5
, 7
: Input Controller
: Presenter 2 3 4
, 6
: Domain Logic 41

42. References
[TWISTING THE TRIAD] Andy Bower, Blair McGlashan, TWISTING THE TRIAD, The evolution of the Dolphin Smalltalk MVP application framework, Tutorial Paper for ESUG 2000,