model view controller pattern patterns model-view-controller

Model View Controller Pattern

• Patterns

• Model-View-Controller

A Single Class

T result = I;T nextValue = getNextValue()while (!isSentinel(nextValue)) { result = f(result, nextValue); nextValue = getNextValue(..);}

Folding Intra-Class PatternLoan, int new ALoan(0), 1

ALoan.add(), *

>= 0

Scanning Inter-Class Pattern

Scanner Instance

Enumeration Interface

Scanner User

public interface <Type>Enumeration { public <Type> nextElement(); public boolean hasMoreElements();

}

Architectural Pattern

• Christopher 79– Each pattern is a three part rule, which

expresses a relation between a certain context, a problem, and a solution.

– Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of a solution to that problem, in such a way that you can use this solution a million times over

Book on Design Patterns

MVC Pattern

Model:APointHistoryModel

instance

Controller:AConsoleControllerinstance

Controller:AnAWTControllerinstance


Controller:ASwingControllerinstance

View:AConsoleViewinstance

View:ABarChartViewinstance

View:APlotterViewinstance

View:Aplotterviewinstance

Displaying Points

Displaying Points

Swing button

AWT button

Swing Detachable Toolbar

Displaying Points

All four views displayed concurrently and kept in Sync.

ObjectEditor-based Structure

APointHistory ObjectEditor

Reusing Point History

APointHistoryUser Interface Code:

Single Main Class

More Modular ApproachEditor:AConsoleEditor

Editor:ASwingPlotterEditor

Editor:ABarChartEditor

Editor:AnAWTPlotterEditor

Composer:Single Main

ClassAPointHistory

Sharing the View

Sharing the Controller

Controller Without View

View Without Controller

Monolithic Editor

AWT Plotter Editor

APointHistory

Separate View and Controller

Controller:AnAWTController

View:ABarchartView

APointHistory

addElement( ) size( )elementAt( )

Performs Input Performs Output

Write methods

Read methods

Multiple Views and Controllers

APointHistory

Controller:AConsoleController



Controller:ASwingController

View:AConsoleView

View:ABarChartView

View:APlotterView

View:APlotterView

Syncing Controllers and Views?

Model View Controller Framework






View:AConsoleView

View:ABarChartView

View:APlotterView

View:APlotterView

Changed object notifies views

ListenableListeners

Model View Controller Framework






View:AConsoleView

View:ABarChartView

View:APlotterView

View:APlotterView


Class

Composer connects models, views, controllers

Class Vs Instance






View:AConsoleView

View:ABarChartView

View:APlotterView

View:APlotterView


Class

Different State

MVC Framework


Instance










Class

Model


Instance










Class

Model Vs PointHistory

APointHistory Instance










Class

Reusing PointHistory

PointHistory APointHistoryIMPLEMENTS

APointHistoryModel

EXTENDS

PointModel

EXTENDS

IMPLEMENTS

Notification Scheme


Instance





• Each view is registered with model.

• Each write method in model calls a notification method in each view.

•Notification method updates display.

Model:PointModel

Instance (Animating Point)

• Each student is registered with professor’s listserv.

• When web page is updated mail sent to students.

•Student reads web page.

View with Multiple Models

APointHistoryModel InstancePointModel

Instance

General Notification Scheme


Instance





•View may have multiple models with common notification method.

•Notification method parameter indicates which model.

Model:PointModel

Instance (Animating Point)

PointHistoryModel & PointHistoryListener

public interface PointHistoryModel extends PointHistory {public void addListener (PointHistoryListener pointHistoryListener);public void removeListener (PointHistoryListener pointHistoryListener);

}

public interface PointHistoryListener {public void pointHistoryUpdated(PointHistory pointHistory);

}

Called whenever model is updatedUpdated object (model)

View (console, barchart, plotter ..)

Common interface of all views

APointHistoryModelimport java.util.Vector;import java.util.Enumeration;public class APointHistoryModel extends APointHistory implements PointHistoryModel {

public void addElement (int x, int y) {super.addElement(x, y);notifyListeners();

}Vector listeners = new Vector();public void addListener (PointHistoryListener pointHistoryListener) {

listeners.addElement(pointHistoryListener);}public void removeListener (PointHistoryListener pointHistoryListener) {

listeners.removeElement(pointHistoryListener);}void notifyListeners() {

Enumeration elements = listeners.elements();while (elements.hasMoreElements())

((PointHistoryListener) elements.nextElement()).pointHistoryUpdated(this);

}}

Object evaluating expression (Object on which enclosing method executed)

Each write method notifies.

Console Viewimport shapes.PointModel;public class APointHistoryConsoleView implements PointHistoryListener {

public void pointHistoryUpdated(PointHistory pointHistory) {System.out.println ("**********");for (int i = 0; i < pointHistory.size(); i++) {

PointModel nextPoint = (PointModel) pointHistory.elementAt(i);

System.out.println("(" + nextPoint.getX() + "," + nextPoint.getY() + ")");

}System.out.println ("**********");

}}

Displaying Points

View updated whenever any controller changes model

Console Controller

public class APointHistoryConsoleController implements PointHistoryConsoleController {

PointHistory pointHistory ;public APointHistoryConsoleController (PointHistory thePointHistory) {

pointHistory = thePointHistory;}public void processCommands() {

while (true){System.out.println("Please enter new point:");String input = Keyboard.readString();if (input.equals("quit")) break;int x = Integer.parseInt(input);int y = Keyboard.readInt();pointHistory.addElement (x,y);

}}

}

Output method not called directly

Console Composerpublic class APointHistoryConsoleComposer { public static void main (String args[]) {

PointHistoryModel pointHistoryModel = new APointHistoryModel();createConsoleEditor(pointHistoryModel);

} public static void createConsoleEditor(PointHistoryModel pointHistoryModel) {

createConsoleView(pointHistoryModel);createConsoleController(pointHistoryModel).processCommands();

} public static PointHistoryListener createConsoleView(PointHistoryModel pointHistoryModel) {

PointHistoryListener pointHistoryView = new APointHistoryConsoleView (); pointHistoryModel.addListener(pointHistoryView); return pointHistoryView; } public static PointHistoryConsoleController createConsoleController(PointHistory pointHistory) {

return new APointHistoryConsoleController(pointHistory); }}

PointHistoryModel & PointHistoryListener


}


}

Using a More Specific Type


}

public interface PointHistoryListener {public void pointHistoryUpdated(PointHistoryModel pointHistoryModel);

}

specific type

Allows less polymorphism

pointHistoryUpdated does not call addListener or removeListener

Using Most General Type Possible


}


}

More general type

Allows more polymorphism

pointHistoryUpdated does not call addListener or removeListener

PointHistoryModel can be assigned

model view controller pattern patterns model-view-controller

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