Software System/Design & Architecture. Eng.Muhammad Fahad Khan Assistant Professor Department of Software Engineering

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1 Software System/Design & Architecture Eng.Muhammad Fahad Khan Assistant Professor Department of Software Engineering

2 Todays lecture Model View Controller (MVC) Copyright M.Fahad Khan 2

3 Model-View-Controller Pattern MVC variants examples Responsibilities of MVC Advantages of MVC Copyright M.Fahad Khan

4 Question Answer Session Lecture 6 Copyright 2012@ M.Fahad Khan

5 MVC Copyright M.Fahad Khan

6 What is MVC? Model View Controller (MVC) is an architecture that separates the representation of information from the user's interaction with it. The model consists of application data and business rules, and the controller mediates input, converting it to commands for the model or view. A view can be any output representation of data, such as a chart or a diagram. Multiple views of the same data are possible, such as a pie chart for management and a tabular view for accountants. Copyright M.Fahad Khan

7 Model-View-Controller Pattern MVC consists of three kinds of objects: Model the application object View UI (screen presentation) Controller defines the way the UI reacts to user inputs Copyright M.Fahad Khan Page 7

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9 10 Million Question

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11 Component interactions In addition to dividing the application into three kinds of components, the MVC design defines the interactions between them. A controller can send commands to its associated view to change the view's presentation of the model (e.g., by scrolling through a document). It can send commands to the model to update the model's state (e.g., editing a document). A model notifies its associated views and controllers when there has been a change in its state. This notification allows the views to produce updated output, and the controllers to change the available set of commands. A passive implementation of MVC omits these notifications, because the application does not require them or the software platform does not support them. A view requests from the model the information that it needs to generate an output representation. Copyright M.Fahad Khan

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13 Component interactions Model. The model manages the behavior and data of the application domain, responds to requests for information about its state (usually from the view), and responds to instructions to change state (usually from the controller). View. The view manages the display of information. Controller. The controller interprets the mouse and keyboard inputs from the user, informing the model and/or the view to change as appropriate. Copyright M.Fahad Khan

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15 The Controller Users interact with the controller. It interprets mouse movement, clicks, keystrokes, etc Communicates those activities to the model eg: delete row, insert row, etc It s interaction with the model indirectly causes the View(s) to update Controllers are a little more complicated. They act as an intermediary between the view objects and the model objects. When a value changes in a model, the controller is responsible for updating the view. Likewise, the controller knows when there s some user input and can update the model data accordingly. Controller objects are often responsible for setup tasks. The models and views must be loaded and initialized at some point, and the central role of the controller makes it a natural candidate for this work. Copyright M.Fahad Khan Page 15

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18 The Controller Example To give you an idea of how this works, imagine an application that plots stock prices: 1. The user clicks a button (view) to refresh the graph. This action is sent to the controller. 2. The controller, in turn, tells the model to load new stock data. 3. The model opens a network connection and begins downloading data. 4. After the stock data is loaded, the model notifies the controller that new data has arrived. 5. The controller passes the new data onto the view, and the user sees the results. Copyright M.Fahad Khan Page 18

19 The Model The MODEL contains the data Has methods to access and possibly update it s contents. Often, it implements an interface which defines the allowed model interactions. Implementing an interface enables models to be pulled out and replaced without programming changes. Models are your application s heart and soul because they re responsible for managing its data. Unlike views, models know nothing about the actions the user is performing or what they re seeing on the display. A model s only function is to manipulate and process the user s data within the application. Models often implement internal logic that provides these basic behaviors. Copyright M.Fahad Khan Page 19

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21 The Model Example For example, whenever you use the built-in Contacts application, you re working with model objects that represent the people in your address book. If you update your application s settings, you re modifying another kind of model object. An application that downloads stock data from the Internet would use a model object to store the price history. Copyright M.Fahad Khan Page 21

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23 The View The VIEW provides a visual representation of the model. There can be multiple views displaying the model at any one time. For example, a companies finances over time could be represented as a table and a graph. These are just two different views of the same data. When the model is updated, all Views are informed and given a chance to update themselves. Copyright M.Fahad Khan Page 23

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26 The View.(contd ) You know all those buttons, scrolling lists, web browsers, and everything else that appears on your iphone screen? Those are all views. Views know how to present your application s data. Some views also know how to react to user input. In many applications, you ll create your own views for displaying specific data. For example, there s no standard widget for displaying stock graphs, so if you want to do that, you ll have to come up with your own solution. Copyright M.Fahad Khan Page 26

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28 The View.(contd ) Likewise, many designers and developers want to customize the look of their application. Whether your motivation is product branding or just wanting to stand out in a crowd, creating a unique look for your app involves building new views based on standard UIView and UIControl classes. Copyright M.Fahad Khan Page 28

29 Example Model-View-Controller talks about the three parts that most websites can be broken down into Controller Entry point of the application. Handles IO. PHP files View Templates displayed to the user. HTML files with PHP Model Functions that interact with the database or perform complex operations. SQL queries in PHP Copyright M.Fahad Khan

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32 DETAILED VISUAL EXAMPLE OF MVC Copyright M.Fahad Khan Page 32

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45 Why use MVC? Makes it very easy to have multiple different displays of the same information. For example: a graph and a table could both display and edit the same data. Essentially provides greater control over the UI and it s behaviour. Copyright M.Fahad Khan Page 45

46 Multiple different displays

47 Model View Controller (MVC) is an architecture, for software development This architecture separates the application logic that the user sees from the user interface. It improves the software development cycle in terms of quality, testing, extensibility and maintenance. The model is manages information and user notifications when information changes. The model is domain-specific to the data which the application operates upon. Domain logic adds functionality to the data. When a model changes its state, it notifies the associated views so they can be updated. Copyright M.Fahad Khan Page 47

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49 MVC Communication Rules Model = What your application is (but not how it is displayed) Controller = How your Model is presented to the user (UI logic) View = Your Controller s minions. Contoller s can always talk directly to their Model. Controller s can also talk directly to their View. The Model and View should never speak to each other. Communication between the View and Controller is blind and structured. The Controller can drop a target on itself, then hand out an action to the View. Copyright M.Fahad Khan Page 49

50 MVC Communication Rules..(cntd..) The View sends the action when things happen in the UI. Sometimes the View needs to synchronize with the Controller. The Controller sets itself as the View s delegate. The delegate is set via a protocol (i.e. it s blind to class). Views do not own the data they display. So, if needed, they have a protocol to acquire it. Controllers are almost always that data source (not Model!). Controllers interpret/format Model information for the View. Copyright M.Fahad Khan Page 50

51 MVC Communication Rules..(cntd..) The Model is (should be) UI independent and should NEVER talk directly to the Controller. If the Model has information (e.g. an update) it uses a radio station like broadcast mechanism that Controllers (or another Model) can tune in to for stuff they re interested in. A View might tune in to a station, but probably not to a Model s. Stick to these rules when building your application and you will have a much better chance of understanding the monster you ve created(!). Copyright M.Fahad Khan Page 51

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53 MVC Variants

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55 Three Tier Model Copyright M.Fahad Khan Page 55

56 N tier Architecture 3 Tier architecture: Presentation Layer Presentation Layer is the layer responsible for displaying user interface. Business Tier Business Tier is the layer responsible for accessing the data tier to retrieve, modify and delete data to and from the data tier and send the results to the presentation tier. This layer is also responsible for processing the data retrieved and sent to the presentation layer. - BLL and DAL Often this layer is divided into two sub layers: the Business Logic Layer (BLL), and the Data Access Layers (DAL). Business Logic Layers are above Data Access Layers, meaning BLL uses DAL classes and objects. DAL is responsible for accessing data and forwarding it to BLL. Data Tier Data tier is the database or the source of the data itself. Common mistakes tightly coupling layers in technology and writing business logic in presentation tier Copyright M.Fahad Khan Page 56

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58 Advantages of MVC Page 58

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60 Advantages of MVC Separating Model from View (that is, separating data representation from presentation) - easy to add multiple data presentations for the same data - facilitates adding new types of data presentation as technology develops. - Model and View components can vary independently enhancing maintainability, extensibility, and testability. The main advantage of adopting a design pattern like MVC is that it allows the code in each unit to be decoupled from the others, making it more robust and immune to changes in other code. Copyright M.Fahad Khan Page 60

61 Advantages of MVC design Pattern Separating Controller from View (application behavior from presentation) - permits run-time selection of appropriate Views based on workflow, user preferences, or Model state. Separating Controller from Model (application behavior from data representation) - allows configurable mapping of user action on the Controller to application functions on the Model. Copyright M.Fahad Khan Page 61

62 Consequences or Benefits Wemake changes without bringing down the server. We leave the core code alone We can have multiple versions of the same data displayed We can test our changes in the actual environment. We have achieved separation of concerns Copyright M.Fahad Khan Page 62

63 Summary of MVC Model - the model represents enterprise data and the business rules that govern access to and updates of this data View -the view renders the contents of a model. It accesses enterprise data through the model and specifies how that data should be presented Controller - the controller translates interactions with the view into actions to be performed by the model Copyright M.Fahad Khan Page 63

64 More Information Copious amounts of information on MVC pattern available on Internet. Examples of MVC (Delegate style) all throughout Swing see JDK doc for details Hope the overview was useful to you! More tutorials, Source-code, etc available at our company web site, We consult and develop applications in many languages, including Java and Microsoft.NET Australian based, Programming world-wide Copyright M.Fahad Khan Page 64

65 References Home of the patterns community Adaptability home page Quickest road to understanding the concepts non-software examples otes/index.htm The Sun location for J2ee Sun s Java Pet store example used Copyright M.Fahad Khan Page 65

66 Assignment 3 Design your own MVC Model for software Product. Due Date : 29 Nov, 2012

67 COMING UP NEXT Architecture-Based Testing and Analysis Software Architects: People and Teams

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