print barcode with vb.net class Stack<T> in C#.NET

Printer Code-128 in C#.NET class Stack<T>

The user of the Stack class puts in the actual type when instantiating the class, like this:

The .NET Framework provides a number of interfaces, such as IEnumerable and ICollection, which the designer of a collection must implement to provide full collection semantics. For example, ICollection allows your collection to be enumerated in a foreach loop. You ll see how these work in a little bit, when we explain the C# collection types. First, though, we re going to show you how to make your own collections, so you can understand how they work.

The goal in creating your own collections is to make them as similar to the standard .NET collections as possible. This reduces confusion, and makes for easier-to-use classes and easier-to-maintain code.

One feature you should provide is to allow users of your collection to add to or extract from the collection with an indexer, just as you would do with an array. For example, suppose you create a ListBox control named myListBox that contains a list of strings stored in a one-dimensional array, a private member variable named

myStrings. A ListBox control contains member properties and methods in addition to its array of strings, so the ListBox itself is not an array. However, it would be convenient to be able to access the ListBox array with an index, just as though the ListBox

itself were an array.* For example, such a property would let you do things like this:

string theFirstString = myListBox[0]; string theLastString = myListBox[Length-1];

An indexer is a C# construct that allows you to treat a class as though it were an array. In the preceding example, you are treating the ListBox as though it were an array of strings, even though it is more than that. An indexer is a special kind of property, but like all properties, it includes get and set accessors to specify its behavior. You declare an indexer property within a class using the following syntax:

type this [type argument]{get; set;}

For example:

public string this[int index] { get {...}; set {...}; }

The return type determines the type of object that will be returned by the indexer, and the type argument specifies what kind of argument will be used to index into the collection that contains the target objects. Although it is common to use integers as index values, you can index a collection on other types as well, including strings. You can even provide an indexer with multiple parameters to create a multidimensional array. The this keyword is a reference to the object in which the indexer appears. As with a normal property, you also must define get and set accessors, which determine how the requested object is retrieved from or assigned to its collection. Example 14-1 declares a ListBox control (ListBoxTest) that contains a simple array (myStrings) and a simple indexer for accessing its contents.

using using using using System; System.Collections.Generic; System.Linq; System.Text;

* The actual ListBox control provided by both Windows Forms and ASP.NET has a collection called Items that is a collection, and it is the Items collection that implements the indexer.

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public class ListBoxTest { private string[] strings; private int ctr = 0; // initialize the ListBox with strings public ListBoxTest( params string[] initialStrings ) { // allocate space for the strings strings = new String[256]; // copy the strings passed in to the constructor foreach ( string s in initialStrings ) { strings[ctr++] = s; } } // add a single string to the end of the ListBox public void Add( string theString ) { if ( ctr >= strings.Length ) { // handle bad index } else strings[ctr++] = theString; } // allow array-like access public string this[int index] { get { if ( index < 0 || index >= strings.Length ) { // handle bad index } return strings[index]; } set { // add new items only through the Add method if ( index >= ctr ) { // handle error } else { strings[index] = value; }