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List<T>.ForEach(Action<T>) Method

  • Reference

Definition

Namespace:
System.Collections.Generic
Assembly:
System.Collections.dll
Assembly:
mscorlib.dll
Assembly:
netstandard.dll
Source:
List.cs
Source:
List.cs
Source:
List.cs

Performs the specified action on each element of the List<T>.

public:
 void ForEach(Action<T> ^ action);
public void ForEach (Action<T> action);
member this.ForEach : Action<'T> -> unit
Public Sub ForEach (action As Action(Of T))

Parameters

action
Action<T>

The Action<T> delegate to perform on each element of the List<T>.

Exceptions

ArgumentNullException

action is null.

InvalidOperationException

An element in the collection has been modified.

Examples

The following example demonstrates the use of the Action<T> delegate to print the contents of a List<T> object. In this example the Print method is used to display the contents of the list to the console.

Note

In addition to displaying the contents using the Print method, the C# example demonstrates the use of anonymous methods to display the results to the console.

List<string> names = new List<string>();
names.Add("Bruce");
names.Add("Alfred");
names.Add("Tim");
names.Add("Richard");

// Display the contents of the list using the Print method.
names.ForEach(Print);

// The following demonstrates the anonymous method feature of C#
// to display the contents of the list to the console.
names.ForEach(delegate(string name)
{
    Console.WriteLine(name);
});

void Print(string s)
{
    Console.WriteLine(s);
}

/* This code will produce output similar to the following:
* Bruce
* Alfred
* Tim
* Richard
* Bruce
* Alfred
* Tim
* Richard
*/

Imports System.Collections.Generic

Class Program
    Shared Sub Main()
        Dim names As New List(Of String)
        names.Add("Bruce")
        names.Add("Alfred")
        names.Add("Tim")
        names.Add("Richard")

        ' Display the contents of the list using the Print method.
        names.ForEach(AddressOf Print)
    End Sub

    Shared Sub Print(ByVal s As String)
        Console.WriteLine(s)
    End Sub
End Class

' This code will produce output similar to the following:
' Bruce
' Alfred
' Tim
' Richard

Remarks

The Action<T> is a delegate to a method that performs an action on the object passed to it. The elements of the current List<T> are individually passed to the Action<T> delegate.

This method is an O(n) operation, where n is Count.

Modifying the underlying collection in the body of the Action<T> delegate is not supported and causes undefined behavior.

Applies to

See also