Programming C# 3.0, 5th Edition

List<T>

The classic problem with the Array type is its fixed size. If you don't know in advance how many objects an array will hold, you run the risk of declaring either too small an array (and running out of room), or too large an array (and wasting memory).

Your program might be asking the user for input, or gathering input from a web site. As it finds objects (strings, books, values, etc.), you will add them to the array, but you have no idea how many objects you'll collect in any given session. The classic fixed-size array is not a good choice, as you can't predict how large an array you'll need.

The List class is an array whose size is dynamically increased as required. Lists provide a number of useful methods and properties for their manipulation. Table 9-3 shows some of the most important ones.

Table 9-3. List methods and properties

Method or property	Purpose
[a]
Capacity	Property to get or set the number of elements the List can contain; this value is increased automatically if count exceeds capacity; you might set this value to reduce the number of reallocations, and you may call Trim( ) to reduce this value to the actual Count
Count	Property to get the number of elements currently in the array
Item( )	Gets or sets the element at the specified index; this is the indexer for the List class[a]
Add( )	Public method to add an object to the List
AddRange( )	Public method that adds the elements of an ICollection to the end of the List
AsReadOnly( )	Public method that returns a read-only instance ...