[Design Pattern] MVC pattern

Model–View–Controller (MVC) is a software architecture,[1] currently considered an architectural pattern used in software engineering. The pattern isolates "domain logic" (the application logic for the user) from the user interface (input and presentation), permitting independent development, testing and maintenance of each (separation of concerns).

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). In event-driven systems, the model notifies observers (usually views) when the information changes so that they can react.

The view renders the model into a form suitable for interaction, typically a user interface element. Multiple views can exist for a single model for different purposes. A viewport typically has a one to one correspondence with a display surface and knows how to render to it.

The controller receives input and initiates a response by making calls on model objects. A controller accepts input from the user and instructs the model and viewport to perform actions based on that input.

An MVC application may be a collection of model/view/controller triads, each responsible for a different UI element. The Swing GUI system, for example, models almost all interface components as individual MVC systems.

MVC is often seen in web applications where the view is the HTML or XHTML generated by the app. The controller receives GET or POST input and decides what to do with it, handing over to domain objects (i.e. the model) which contain the business rules and know how to carry out specific tasks such as processing a new subscription, and which hand control to (X)HTML-generating components such as templating engines, XML pipelines, AJAX callbacks, etc.

The model is not a database: the 'model' in MVC is both the data and the business/domain logic needed to manipulate the data in the application. Many applications use a persistent storage mechanism such as a database to store data. MVC does not specifically mention the data access layer because it is understood to be underneath or encapsulated by the model. Models are not data access objects; however, in very simple apps that have little domain logic there is no real distinction to be made. Active Record is an accepted design pattern which merges domain logic and data access code - a model which knows how to persist itself.

MVC sample code download 1

MVC sample code download 2

[Design Pattern] Facade Pattern

The facade pattern is a software engineering design pattern commonly used with Object-oriented programming. (The name is by analogy to an architectural facade.)

A facade is an object that provides a simplified interface to a larger body of code, such as a class library. A facade can:

make a software library easier to use, understand and test, since the facade has convenient methods for common tasks;
make code that uses the library more readable, for the same reason;
reduce dependencies of outside code on the inner workings of a library, since most code uses the facade, thus allowing more flexibility in developing the system;
wrap a poorly-designed collection of APIs with a single well-designed API (as per task needs).

Sample Code download

[.NET] StackTrace with Exception

When a programmer develop .NET, he can use Exception.StatckTrace to get stack trace information.

Represents a stack trace, which is an ordered collection of one or more stack frames.

MSDN Remark has some information:

StackTrace information will be most informative with Debug build configurations. By default, Debug builds include debug symbols, while Release builds do not. The debug symbols contain most of the file, method name, line number, and column information used in constructing StackFrame and StackTrace objects.

using System;
class Orz
{ 
  public static void Main()
  {
     try
     {
        XD();
     }
     catch( Exception e )
     {
      Console.WriteLine( "System.Exception stack trace = \n{0}", e.StackTrace );
     }
  }
  static void XD()
  {
      throw new Exception( "XD() has some error" );
  }
}

Output:
System.Exception stack trace =
at Orz.XD()
at Orz.Main()