2. Design Patterns| What is a Pattern?
A Design Pattern is essentially a
description of a commonly occurring
object-oriented design problem and how
to solve it
3. Design Patterns| An object-oriented design problem
Imagine a system that uses a number of temperature sensors to monitor the condition of a
hardware device of some sort.
The first model of the device uses Indus, Inc. TS7000 sensors.
Indus supplies a simple Java class to interface with the sensors:
class TS7000 {
native double getTemp();
...
}
Here is some monitoring code that simply calculates the mean temperature reported by the sensors.
double sum = 0.0;
for (int i = 0; i < sensors.length; i++)
sum += sensors[i].getTemp();
double meanTemp = sum / sensors.length;
Note that sensors is declared as an array of TS7000 objects.
(TS7000 sensors[ ] = new TS7000[...])
4. Design Patterns| An object-oriented design problem
The second model of the device uses more temperature sensors and the design uses a mix of
TS7000s and sensors from a new vendor, eSoft.
The eSoftsensors are SuperTemps and a hardware interfacing class is supplied:
class SuperTempReader {
//
// NOTE: temperature is Celsius tenths of a degree
//
native double current_reading();
...
}
Here is a terrible way to accommodate both types of sensors:
for (int i = 0; i < sensors.length; i++)
{
if (sensors[i] typeof TS7000)
sum += ((TS7000)sensors[i]).getTemp();
else
// Must be a SuperTemp!
sum +=
((SuperTempReader)sensors[i]).current_reading() * 10;
}
In this case sensors is an array of Objects. The type is tested with
typeof and an appropriate cast and method call is performed.
5. Design Patterns| A pattern to the rescue!
Any problems here?
What's terrible about this code?
Which pattern is suitable for it?
Types of Patterns
- Classification
- GOF
6. Design Patterns| Patterns for Web application development
Web development Issues
- automated testing
- UI are hard to test
- Changing nature of web
- Frequent changes in UI Design
How to solve this issue?
- Separate UI and Business Objects
MVC
- Model View Controller
MVP
- Model View Presenter
7. Design Patterns| Model – View - Controller
Request
Response
nd Controller
ma
ta
De
Da
Model View
8. Design Patterns| Model – View - Presenter
Model
Demand
Data
Presenter
View Interface
View
Implementation Response
Request
9. Design Patterns| ASP.NET MVC 3
A part of the ASP.NET Web application framework
It enables clean separation of concerns, testability, and
TDD by default
It is highly extensible and pluggable
10. Design Patterns| Web Client Software Factory
Quickly incorporate many of the proven practices and patterns of building
Web client applications
Provides proven solutions to common challenges found while building and
operating large transaction processing enterprise Web sites
Support for the Model-View-Presenter pattern
Contains a collection of
reusable components and libraries,
Visual Studio 2005 and Visual Studio 2008 solution templates, wizards and extensions,
How-to topics,
automated tests,
extensive architecture documentation,
patterns,
and a reference implementation
