Friday, November 16, 2012

Observer Design Pattern using Delegates/events

Today I want to discuss with you how to implement Observer design pattern using delegate and event in /c#.

Observer Pattern

The observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods. It is mainly used to implement distributed event handling systems. The Observer pattern is also a key part in the familiar Model View Controller (MVC) architectural pattern.(wikipedia).

UML class diagram of Observer pattern(wikipedia)

The Observer Pattern describes the dependence relationship between one object (observable) to many objects (observers). It's also called Model/View, Dependents, or Distributor/Listener pattern.This article introduces an implementation when we can use the Observer pattern to keep all observer objects updated after things have changed.

Case project

In this case, patient is an ObservableObject that needs to send out the notification when the hospital updates his/her physical status. The hospital will determine who will be notified when the patient status is updated.

Thursday, November 15, 2012

A Custom Attribute based approach to write summary on business object

Last day, I have got a mail from a junior developer he needs some help about custom attributes. He has no previous experience about it. I have delivered his some speech or send some link for study. Today I have made an example for him, so that he can understand its usage very easily. Now this also share with you it may also help other friends.

using System;

Method 'StartWorkflowOnListItem' in type 'Microsoft.SharePoint.WorkflowServices.FabricWorkflowInstanceProvider'

Exception: Method 'StartWorkflowOnListItem' in type 'Microsoft.SharePoint.WorkflowServices.FabricWorkflowInstanceProvider'...