OOP Class12

Dymnically Adding Elements

http://www.c-sharpcorner.com/UploadFile/Saurabh.Mishra/GenericsInC2PartI04122006074306AM/GenericsInC2PartI.aspx

Say we have an empty drop down list.

<asp:DropDownList id="ddlCheese" autopostback="True" runat="server"  />

Since we know that all Lists in the framework contain ListItems we can dymaically add a bunch of cheeses by using a for loop that creates and add ListItems.

ListItem has several constuctors

Visibility	Constructor	Parameters
public	ListItem	( )
public	ListItem	( String text )
public	ListItem	( String text , String value )
public	ListItem	( String text , String value , Boolean enabled )

<csharp>

       //an array of names of cheese
       string [] aryNames = new string[5];
         
       aryNames [0] = "Feta";
       aryNames [1] = "Colby";
       aryNames [2] = "Gruyere";
       aryNames [3] = "Edam";
       aryNames [4] = "Colby";

       foreach (string cheeseName in aryNames)
       {
           ListItem newItem = new ListItem(cheeseName, cheeseName);   //get a new list item 
                                                   //with i for string text and i for value
           ddlCheese.Items.Add(newItem);   
       }</csharp>

CheeseArray.aspx - source

<csharp>//an arraylist of cheesew

       Cheese Feta = new Cheese("Feta");
       Cheese Colby = new Cheese("Colby");
       Cheese Gruyere = new Cheese("Gruyere");
       Cheese Edam = new Cheese("Edam");
       
       
       ArrayList alCheeses = new ArrayList();
       alCheeses.Add(Feta);
       alCheeses.Add(Colby);
       alCheeses.Add(Gruyere);
       alCheeses.Add(Edam);</csharp>

and the cheese class <csharp>public class Cheese {

   public string Name;
   public  Milks MilkType;
   public string Region;
   
   public Cheese()
   {
   }
   
   public Cheese(string name)
   {
       this.Name = name;
   }
   
   public enum Milks { Cows, Goats, Mix, Vegetarian }

}</csharp>

Then you can bind the new cheese arraylist to a dropdown box.

CheeseObject.aspx - source

Observer

Observer is a deisgn pattern that is often used to publish (push) or subcribe (pull) changes in the stae of one object to other intersted object. It encourgaes loose coupling of objects.

The object the get the data often called the subject then notifies the observing objects of the change. The observing object will often repond to the subject.

Here is a real example in c#. In this exmaple a stock (the subject) notifies and investor (the observer) of a change in price.