test first guis

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Copyright2008-2009 Robert Walsh - All Rights Reserved

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Test First GUIsUsing Model-View-Presenter

Robert Walsh - President - EnvisionWare, [email protected]


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3Agenda

What is Model-View-Presenter

Benefits of MVP

Implementing MVP

Using MVP to Test User Interfaces

Implementing MVP with Win32

Summary


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4What isModel-View-Presenter?


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A development technique for separating data,logic, display, and user interaction from one

another Model holds data

View displays data

Presenterconnects the model to the view

Presenter supplies the logic for manipulating the

data and updating the display


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User Input External Stimulus

Notificationof change

What isModel-View-Presenter?


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Classic MVC doesnt work well with the modern rich clienttools because they design things so that the view handles allthe user events such as mouse and keyboard clicks. InModel View Presenter, the view continues to handle these,but then immediately delegates these to the presenter. Thepresenter then decides what to do with the event,

communicating with the domain and the data in the viewscontrols.

- Martin Fowler

Source: http://www.martinfowler.com/eaaDev/ModelViewPresenter.html

What isModel-View-Presenter?

What about Model-View-Controller?


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Upon further study and reflection, I decided that the patternthat was here under the name Model View Presenterneeded to be split, so I have seperated (sic) it intoSupervising Controller and Passive View. You can find adiscussion of the origins of Model-View-Presenter in thecontext of architecutres (sic) here:

(http://www.martinfowler.com/eaaDev/uiArchs.html).

- Martin Fowler, July 2006

What is Model-View-Presenter?

Additional comments from Martin Fowler


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11Benefits of MVP


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12Benefits of MVP

Decoupling

Business logic, data persistence, and user interface

are kept isolated from one another Different teams may work on each part without

depending on the other two


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13Benefits of MVP

Flexibility

Want a fresh new look?

Change the View

Model and Presenter remain unchanged

Need to change how the data is stored?

Change the Model

View and Presenter remain unchanged


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14Benefits of MVP

Re-use

The same Model and Presenter might be used for a

traditional thick client or for a web-based front-end


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15Benefits of MVP

Testability

Each component of the MVP triad may be tested

independently from the other two Automated GUI testing is possible with scripts that

rely on the layout of the interface


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16Implementing MVP


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19Implementing MVP

The Presenter

Holds references to the Model and the View

Uses data from the Model to initialize the View

User input is passed from the View to the Presenter,

and the Presenter decides what to do with it

Some user actions may cause the Presenter to

update the Model

Some external stimuli may cause the Model tonotify the Presenter that it should update the View


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20

Presenter

theView

theModel

ModelViewthePresenter

Implementing MVP


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21Implementing MVP

Psuedo-code for initializing an MVP triad


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22Implementing MVP

Psuedo-code for the Presenters constructor


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23Using MVP to Test UserInterfaces


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24

IPresenter

theView

theModel

IModel

IView

thePresenter

Presenter MockPresenter

Model MockModel

View MockView

SensingView

Using MVP to Test UserInterfaces


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25Using MVP to Test UserInterfaces?

A simple example


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If we are testing the Model

The model can typically be tested through

traditional unit testing processes The model typically does not interact directly with

the View or the Presenter


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The MVP approach allows the tester to simulateconditions that are difficult to induce the the

real world Database errors

Networking problems

Exceptions


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Key points

What is being tested with MVP are the interactions

between the Model, View, and Presenter The actual behaviors should be tested with each

piece in complete isolation

For example:

Does view.setAddress(addressData) really

set the text of the address control?

Does model.getCustomer(customerId)

really get customer information from the

database?


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37Demonstration


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38Implementing MVP withWin32


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Win32 presents a challenge

Traditional DlgProc does not function well in the role

of the View The code handling the UI is procedural, not

object-based

Delegating input events to the Presenter is no

problem, but allowing the Presenter to manipulate

the View requires that the Presenter know more

about the View than it should Specifically, the Presenter would have to know

about the individual dialog controls and their IDs


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A solution

Introduce a ViewProxy to serve as an interface

between the DlgProc and the Presenter Input events will be handed to the ViewProxy, and

the ViewProxy will hand them to the Presenter

The Presenter will manipulate the ViewProxy, and

the ViewProxy will manipulate the actual controls

on the dialog


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41

Presenter

ModelView

ViewProxy

DlgProc

Implementing MVP withWin32


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45Summary


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46Summary

Model

Represents data

View

Represents user interface

Presenter

Handles user input by interacting with the Model and

updating the View


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47Summary

Benefits

Decoupling

Data, logic, and presentation are separated Flexibility

Persistence and look-and-feel are easily changed

Re-use

Models and Presenters may be used with multiple

Views Testability

Facilitates GUI testing at the Presenter and the

View


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48Summary

Implementation

Presenter initializes View with data from Model

View tells Presenter when user interacts with View

Presenter gets information from Model and updates

View


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49Questions


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50Resources

Feathers, Michael (2002). Humble Dialog Box, The. [Online]. http://www.objectmentor.com/resources/articles/

TheHumbleDialogBox.pdf

Fowler, Martin (July 2004). Model View Presenter. [Online]. http://www.martinfowler.com/eaaDev/ModelViewPresenter.html

Gamma, Erich et al. Design Patterns. Boston, MA: Addison-Wesley,1995.

Lambert, Kenneth A. and Martin Osborne. Smalltalk in Brief Introduction to Object-Oriented Software Development. Boston, MA:PWS Publishing Company, 1997.

Lewis, Simon. Art and Science of Smalltalk, The. London: Prentice HallInternational, 1995.

Pinson, Lewis J. and Richard S. Wiener. Introduction to Object-Oriented Programming and Smalltalk, An. Reading, MA:Addison-Wesley, 1988.


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51Thank you!

For more information:

Robert Walsh

PresidentEnvisionWare, Inc.

678-584-5911

[email protected]://www.envisionware.com

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