ArrayList.IndexOf Method (Object)
Namespace: System.Collections
Assembly: mscorlib (in mscorlib.dll)
Parameters
- value
- Type: System.Object
The Object to locate in the ArrayList. The value can be null.
Return Value
Type: System.Int32The zero-based index of the first occurrence of value within the entire ArrayList, if found; otherwise, -1.
Implements
IList.IndexOf(Object)The ArrayList is searched forward starting at the first element and ending at the last element.
This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.
This method determines equality by calling Object.Equals.
Starting with the .NET Framework 2.0, this method uses the collection’s objects’ Equals and CompareTo methods on item to determine whether item exists. In the earlier versions of the .NET Framework, this determination was made by using the Equals and CompareTo methods of the item parameter on the objects in the collection.
The following code example shows how to determine the index of the first occurrence of a specified element.
using System; using System.Collections; public class SamplesArrayList { public static void Main() { // Creates and initializes a new ArrayList with three elements of the same value. ArrayList myAL = new ArrayList(); myAL.Add( "the" ); myAL.Add( "quick" ); myAL.Add( "brown" ); myAL.Add( "fox" ); myAL.Add( "jumps" ); myAL.Add( "over" ); myAL.Add( "the" ); myAL.Add( "lazy" ); myAL.Add( "dog" ); myAL.Add( "in" ); myAL.Add( "the" ); myAL.Add( "barn" ); // Displays the values of the ArrayList. Console.WriteLine( "The ArrayList contains the following values:" ); PrintIndexAndValues( myAL ); // Search for the first occurrence of the duplicated value. String myString = "the"; int myIndex = myAL.IndexOf( myString ); Console.WriteLine( "The first occurrence of \"{0}\" is at index {1}.", myString, myIndex ); // Search for the first occurrence of the duplicated value in the last section of the ArrayList. myIndex = myAL.IndexOf( myString, 4 ); Console.WriteLine( "The first occurrence of \"{0}\" between index 4 and the end is at index {1}.", myString, myIndex ); // Search for the first occurrence of the duplicated value in a section of the ArrayList. myIndex = myAL.IndexOf( myString, 6, 6 ); Console.WriteLine( "The first occurrence of \"{0}\" between index 6 and index 11 is at index {1}.", myString, myIndex ); // Search for the first occurrence of the duplicated value in a small section at the end of the ArrayList. myIndex = myAL.IndexOf( myString, 11 ); Console.WriteLine( "The first occurrence of \"{0}\" between index 11 and the end is at index {1}.", myString, myIndex ); } public static void PrintIndexAndValues(IEnumerable myList) { int i = 0; foreach (Object obj in myList) Console.WriteLine(" [{0}]: {1}", i++, obj); Console.WriteLine(); } } /* This code produces output similar to the following: The ArrayList contains the following values: [0]: the [1]: quick [2]: brown [3]: fox [4]: jumps [5]: over [6]: the [7]: lazy [8]: dog [9]: in [10]: the [11]: barn The first occurrence of "the" is at index 0. The first occurrence of "the" between index 4 and the end is at index 6. The first occurrence of "the" between index 6 and index 11 is at index 6. The first occurrence of "the" between index 11 and the end is at index -1. */
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
