List<T>.ForEach(Action<T>) 方法

定義

List<T> 的每一個項目上執行指定之動作。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))

參數

action
Action<T>

要在 List<T> 的每一個項目上執行的 Action<T> 委派。The Action<T> delegate to perform on each element of the List<T>.

例外狀況

actionnullaction is null.

集合中的項目已經過修改。An element in the collection has been modified.

範例

下列範例示範 Action<T> 如何使用委派來列印物件的內容 List<T>The following example demonstrates the use of the Action<T> delegate to print the contents of a List<T> object. 在此範例中, Print 會使用方法將清單的內容顯示到主控台。In this example the Print method is used to display the contents of the list to the console.

注意

除了使用方法顯示內容之外 Print ,c # 範例也會示範如何使用 匿名方法 將結果顯示在主控台中。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

備註

Action<T>是方法的委派,這個方法會在傳遞給它的物件上執行動作。The Action<T> is a delegate to a method that performs an action on the object passed to it. 目前的專案 List<T> 會個別傳遞給 Action<T> 委派。The elements of the current List<T> are individually passed to the Action<T> delegate.

此方法是 O (n) 作業,其中 nCountThis method is an O(n) operation, where n is Count.

不支援修改委派主體中的基礎集合 Action<T> ,而且會造成未定義的行為。Modifying the underlying collection in the body of the Action<T> delegate is not supported and causes undefined behavior.

適用於

另請參閱