System.Collections.ArrayList

Added in .NET 1.1
This allows you to work with a set of values as if they were an array and a collection at the same time.

System.Collections.ArrayList myArrayList; 

Represents a collection of items whose size can be changed dynamically.

ArrayList vs Array

An arraylist is a combination of an array and a collection.
Imagine that you need to keep track of various objects but you have no idea how many.
It is difficult to use an array for this purpose because you must declare the size of the array at compile time.
This is an aray whose size is dynamically increased as required.

Features

An arraylist has the following functionality:
You can address a value by its index
You can quickly sort and reverse the list
You can search sequentially
You can append elements to the end and insert them in a particular position

Different Data Types

These items can have different data types.

System.Collections.ArrayList myArrayList; 
myArrayList = new System.Collections.ArrayList(); 
myArrayList.Add("string"); 
myArrayList.Add(20); 
myArrayList.Add(false); 
Console.WriteLine(myArrayList[1]); 

Do not return null ?

return new System.Collections.ArrayList 

Methods

Properties

Generic Version

The generic version of this collection is System.Collections.Generic.List

Adding

Initailising ArrayLists

The default capacity for a new arraylist is 16 elements.

System.Collections.ArrayList myArrayList; 
myArrayList = new System.Collections.ArrayList(); 

Accessing Elements - Zero Based

Items can be returned using an index that starts at zero.

System.Collections.ArrayList myArrayList; 
myArrayList = new System.Collections.ArrayList(); 
myArrayList.Add("string"); 
myArrayList.Add(20); 
myArrayList.Add(false); 
Console.WriteLine(myArrayList[1]); 

Capacity

You should always try and define an initial capacity for your arraylist if possible.
You can modify the capacity at any time by assigning a value to the Capacity property

myArrayList.Capacity = myArrayList.Count 

Another way to achieve the same result is to use the TrimToSize property

myArrayList.TrimToSize 

When the current capacity is exceeded the ArrayList will automatically double its capacity.

Inserting

Insert - Inserts an element at the specified index.
InsertRange -

Removing

There are two ways you can remove all the instances of an element.

Remove

The Remove method will only remove the first occurrence of an element.

myArrayList.Remove("string"); 

while (myArrayList.IndexOf("remove this") >= 0) 
{ 
   myArrayList.Remove("remove this"); 
} 

RemoveAt

myArrayList.RemoveAt(1); 

Also this method does not generate an exception if the element you want to remove cannot be found.

RemoveRange

Finding

System.Collections.ArrayList myArrayList = new System.Collections.ArrayList(); 
myArrayList.Add("GBP"); 
myArrayList.Add("USD"); 
myArrayList.Add("EUR"); 
Console.WriteLine(myArrayList[1]); 

Contains

Does an Element Exist

if (myArrayList.Contains(sElement) == true) 
{ 
} 

IndexOf

Returns the index of the element in the collection, or -1 if it cannot be found.

LastIndexOf

Updating

Looping

for

for (int icount = 0; icount < myArrayList.Count; icount++) 
{ 
   System.Console.WriteLine(myArrayList[icount]); 
} 

for - each

foreach (string element in myArrayList) 
{ 
   System.Console.WriteLine(element); 
} 

while

do - while

This loops until the count property becomes constant.

int isavecount; 
do 
{ 
   isavecount = alsArrayListStrings.Count; 
   myArrayList.Remove("remove this"); 
} while (alsArrayListStrings.Count < isavecount) 

Converting

Converting to a String Array

string[] arValues; 
System.Collections.ArrayList myArrayList; 
arValues = (string[])arArrayList.ToArray(GetType(String))