Array to List C#

In C#, the ArrayList is a non-generic collection of objects whose size increases dynamically. It is the same as Array except that its size increases dynamically.

An ArrayList can be used to add unknown data where you don't know the types and the size of the data.

Create an ArrayList

The ArrayList class included in the System.Collections namespace. Create an object of the ArrayList using the new keyword.

using System.Collections; ArrayList arlist = new ArrayList[]; // or var arlist = new ArrayList[]; // recommended

Adding Elements in ArrayList

Use the Add[] method or object initializer syntax to add elements in an ArrayList.

An ArrayList can contain multiple null and duplicate values.

// adding elements using ArrayList.Add[] method var arlist1 = new ArrayList[]; arlist1.Add[1]; arlist1.Add["Bill"]; arlist1.Add[" "]; arlist1.Add[true]; arlist1.Add[4.5]; arlist1.Add[null]; // adding elements using object initializer syntax var arlist2 = new ArrayList[] { 2, "Steve", " ", true, 4.5, null };

Use the AddRange[ICollection c] method to add an entire Array, HashTable, SortedList, ArrayList, BitArray, Queue, and Stack in the ArrayList.

var arlist1 = new ArrayList[]; var arlist2 = new ArrayList[] { 1, "Bill", " ", true, 4.5, null }; int[] arr = { 100, 200, 300, 400 }; Queue myQ = new Queue[]; myQ.Enqueue["Hello"]; myQ.Enqueue["World!"]; arlist1.AddRange[arlist2]; //adding arraylist in arraylist arlist1.AddRange[arr]; //adding array in arraylist arlist1.AddRange[myQ]; //adding Queue in arraylist

Accessing an ArrayList

The ArrayList class implements the IList interface. So, elements can be accessed using indexer, in the same way as an array. Index starts from zero and increases by one for each subsequent element.

An explicit casting to the appropriate types is required, or use the var variable.

var arlist = new ArrayList[] { 1, "Bill", 300, 4.5f }; //Access individual item using indexer int firstElement = [int] arlist[0]; //returns 1 string secondElement = [string] arlist[1]; //returns "Bill" //int secondElement = [int] arlist[1]; //Error: cannot cover string to int //using var keyword without explicit casting var firstElement = arlist[0]; //returns 1 var secondElement = arlist[1]; //returns "Bill" //var fifthElement = arlist[5]; //Error: Index out of range //update elements arlist[0] = "Steve"; arlist[1] = 100; //arlist[5] = 500; //Error: Index out of range

Iterate an ArrayList

The ArrayList implements the ICollection interface that supports iteration of the collection types. So, use the foreach and the for loop to iterate an ArrayList. The Count property of an ArrayList returns the total number of elements in an ArrayList.

ArrayList arlist = new ArrayList[] { 1, "Bill", 300, 4.5F }; foreach [var item in arlist] Console.Write[item + ", "]; //output: 1, Bill, 300, 4.5, for[int i = 0 ; i < arlist.Count; i++] Console.Write[arlist[i] + ", "]; //output: 1, Bill, 300, 4.5,

Insert Elements in ArrayList

Use the Insert[] method to insert an element at the specified index into an ArrayList.

Signature: void Insert[int index, Object value]

ArrayList arlist = new ArrayList[] { 1, "Bill", 300, 4.5f }; arlist.Insert[1, "Second Item"]; foreach [var val in arlist] Console.WriteLine[val];

Use the InsertRange[] method to insert a collection in an ArrayList at the specfied index.

Signature: Void InsertRange[int index, ICollection c]

ArrayList arlist1 = new ArrayList[] { 100, 200, 600 }; ArrayList arlist2 = new ArrayList[] { 300, 400, 500 }; arlist1.InsertRange[2, arlist2]; foreach[var item in arlist1] Console.Write[item + ", "]; //output: 100, 200, 300, 400, 500, 600,

Use the Remove[], RemoveAt[], or RemoveRange methods to remove elements from an ArrayList.

ArrayList arList = new ArrayList[] { 1, null, "Bill", 300, " ", 4.5f, 300, }; arList.Remove[null]; //Removes first occurance of null arList.RemoveAt[4]; //Removes element at index 4 arList.RemoveRange[0, 2];//Removes two elements starting from 1st item [0 index]

Check Element in ArrayList

Use the Contains[] method to determine whether the specified element exists in the ArrayList or not. It returns true if exists otherwise returns false.

ArrayList arList = new ArrayList[] { 1, "Bill", 300, 4.5f, 300 }; Console.WriteLine[arList.Contains[300]]; // true Console.WriteLine[arList.Contains["Bill"]]; // true Console.WriteLine[arList.Contains[10]]; // false Console.WriteLine[arList.Contains["Steve"]]; // false

It is not recommended to use the ArrayList class due to performance issue. Instead, use List to store heterogeneous objects. To store data of same data type, use Generic List.

ArrayList Class

The following diagram illustrates the ArrayList class.

ArrayList Properties

ArrayList Methods