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Published byNorah Harvey Modified over 9 years ago
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MVC CompSci 230 S2 2015 Software Construction
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MVC Architecture A typical application includes software to maintain application data, document text in a word processor state of a chess game -- positions of pieces present output outline view or print preview in a word processor graphical view of chess game process user input key presses mouse click on controls 132
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Swing’s Model-based Architecture “Swing architecture is rooted in the model-view-controller (MVC) design that dates back to SmallTalk. “MVC architecture calls for a visual application to be broken up into three separate parts: A model that represents the data for the application The view that is the visual representation of that data A controller that takes user input on the view and translates that to changes in the model.” [Amy Fowler, ibid.] 133
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MVC: According to Wikipedia A controller can send commands to the model to update the model's state (e.g., editing a document). It can also send commands to its associated view to change the view's presentation of the model (e.g., by scrolling through 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. In some cases an MVC implementation may instead be 'passive' and other components must poll the model for updates rather than being notified. A view requests information from the model that it uses to generate an output representation to the user. 134
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Model-View-Controller (MVC) Data model Data displayUser input Model ViewController UI: Data: manipulate refresh events 135
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Spaghetti Code vs Modular Design Spaghetti Code Haphazard connections, probably grown over time No visible cohesive groups High coupling: high interaction between random parts Understand it: all or nothing Modular System High cohesion within modules Low coupling between modules Modules can be understood separately Interaction between modules is easily-understood and thoroughly specified Both examples have 10 modules and 13 connections! 136
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E.g. C# TreeView Control TreeView control Nodes collection treeView1.Nodes Java: model listeners Model View Controller 137
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Multiple Views Model View Controller View Controller 138
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Typical real-world approach Sometimes the Controller and View are combined, especially in small programs Combining the Controller and View is appropriate if they are very interdependent The Model should still be independent Never mix Model code with GUI code! Data model Data displayData manipulation logic Model ViewController 139
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E.g. C# TreeView Control TreeView control Nodes collection treeView1.Nodes Java: model listeners Model View Controller 1310
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C# DataBase Controls DataSet class -tables -columns -rows DataGrid control -scroll, sort, edit, … Model View Controller DB 1311
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MVC Example in Java Example: JList A javax.swing.ListModel is an object which maintains a list of objects: it knows how big the list is, which object is where in the list, etc, and can insert/remove objects A javax.swing.JList is a graphical component giving a view of the list and able to receive user input to modify the list DefaultList Model Javax.swing. JList modifies notifies DefaultListModel > AbstractListModel > Javax.swing.ListModel isEmpty(): boolean getSize(): int addElement(Object) removeElement(Object) elementAt(): Object removeElementAt(int) insertElementAt(int) indexOf(Object): int etc JList Javax.swing.JComponent 1312
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