Action Action Action Action Delegate

定义

封装一个方法,该方法不具有参数并且不返回值。Encapsulates a method that has no parameters and does not return a value.

public delegate void Action();
public delegate void Action();
type Action = delegate of unit -> unit
Public Delegate Sub Action()
继承

注解

您可以使用此委托以参数的形式传递方法, 而无需显式声明自定义委托。You can use this delegate to pass a method as a parameter without explicitly declaring a custom delegate. 封装的方法必须对应于由此委托定义的方法签名。The encapsulated method must correspond to the method signature that is defined by this delegate. 这意味着封装的方法必须没有任何参数, 并且不能有返回值。This means that the encapsulated method must have no parameters and no return value. (在C#中, 该方法必须void返回。(In C#, the method must return void. 在 Visual Basic 中, 它必须由Sub...End SubIn Visual Basic, it must be defined by the SubEnd Sub 构造.construct. 它也可以是返回忽略的值的方法。)通常, 这种方法用于执行操作。It can also be a method that returns a value that is ignored.) Typically, such a method is used to perform an operation.

备注

若要引用没有参数并返回值的方法, 请改用泛型Func<TResult>委托。To reference a method that has no parameters and returns a value, use the generic Func<TResult> delegate instead.

使用Action委托时, 无需显式定义用于封装无参数过程的委托。When you use the Action delegate, you do not have to explicitly define a delegate that encapsulates a parameterless procedure. 例如, 下面的代码显式声明一个名为ShowValue的委托, 并将对该Name.DisplayToWindow实例方法的引用分配给它的委托实例。For example, the following code explicitly declares a delegate named ShowValue and assigns a reference to the Name.DisplayToWindow instance method to its delegate instance.

using namespace System;
using namespace System::Windows::Forms;

public delegate void ShowValue();


public ref class Name
{
private:
   String^ instanceName;

public:
   Name(String^ name) 
   {
      instanceName = name;
   }

   void DisplayToConsole()
   {
      Console::WriteLine(this->instanceName);
   }

   void DisplayToWindow()
   {
      MessageBox::Show(this->instanceName);
   }
};

int main()
{
   Name^ testName = gcnew Name(L"Koani");
   ShowValue^ showMethod;
   showMethod = gcnew ShowValue(testName, &Name::DisplayToWindow);
   showMethod();
   return 0;
}
using System;
using System.Windows.Forms;

public delegate void ShowValue();

public class Name
{
   private string instanceName;
   
   public Name(string name)
   {
      this.instanceName = name;
   }

   public void DisplayToConsole()
   {
      Console.WriteLine(this.instanceName);
   }

   public void DisplayToWindow()
   {
      MessageBox.Show(this.instanceName);
   }
}

public class testTestDelegate
{
   public static void Main()
   {
      Name testName = new Name("Koani");
      ShowValue showMethod = testName.DisplayToWindow;
      showMethod();
   }
}
Public Delegate Sub ShowValue

Public Class Name
   Private instanceName As String
   
   Public Sub New(name As String)
      Me.instanceName = name
   End Sub
   
   Public Sub DisplayToConsole()
      Console.WriteLine(Me.instanceName)
   End Sub   
   
   Public Sub DisplayToWindow()
      MsgBox(Me.instanceName)
   End Sub   
End Class

Public Module testDelegate
   Public Sub Main()
      Dim testName As New Name("Koani")
      Dim showMethod As ShowValue = AddressOf testName.DisplayToWindow
      showMethod   
   End Sub
End Module

下面的示例通过实例化Action委托来简化此代码, 而不是显式定义一个新委托并为其分配一个命名方法。The following example simplifies this code by instantiating the Action delegate instead of explicitly defining a new delegate and assigning a named method to it.

#using <System.Windows.Forms.dll>

using namespace System;
using namespace System::Windows::Forms;

public ref class Name
{
private:
   String^ instanceName;
   
public:
   Name(String^ name)
   {
      instanceName = name;
   }

   void DisplayToConsole()
   {
      Console::WriteLine(this->instanceName);
   }

   void DisplayToWindow()
   {
      MessageBox::Show(this->instanceName);
   }
};


int main()
{
   Name^ testName = gcnew Name(L"Koani");
   System::Action^ showMethod;
   showMethod += gcnew Action(testName, &Name::DisplayToWindow);
   showMethod();
   return 0;
}
using System;
using System.Windows.Forms;

public class Name
{
   private string instanceName;
   
   public Name(string name)
   {
      this.instanceName = name;
   }

   public void DisplayToConsole()
   {
      Console.WriteLine(this.instanceName);
   }

   public void DisplayToWindow()
   {
      MessageBox.Show(this.instanceName);
   }
}

public class testTestDelegate
{
   public static void Main()
   {
      Name testName = new Name("Koani");
      Action showMethod = testName.DisplayToWindow;
      showMethod();
   }
}
Public Class Name
   Private instanceName As String
   
   Public Sub New(name As String)
      Me.instanceName = name
   End Sub
   
   Public Sub DisplayToConsole()
      Console.WriteLine(Me.instanceName)
   End Sub   
   
   Public Sub DisplayToWindow()
      MsgBox(Me.instanceName)
   End Sub   
End Class

Public Module testDelegate
   Public Sub Main()
      Dim testName As New Name("Koani")
      Dim showMethod As Action = AddressOf testName.DisplayToWindow
      showMethod   
   End Sub
End Module

你还可以在中Action C#将委托与匿名方法一起使用, 如下面的示例所示。You can also use the Action delegate with anonymous methods in C#, as the following example illustrates. (有关匿名方法的介绍, 请参阅匿名方法。)(For an introduction to anonymous methods, see Anonymous Methods.)

using System;
using System.Windows.Forms;

public class Name
{
   private string instanceName;
   
   public Name(string name)
   {
      this.instanceName = name;
   }

   public void DisplayToConsole()
   {
      Console.WriteLine(this.instanceName);
   }

   public void DisplayToWindow()
   {
      MessageBox.Show(this.instanceName);
   }
}

public class Anonymous
{
   public static void Main()
   {
      Name testName = new Name("Koani");
      Action showMethod = delegate() { testName.DisplayToWindow();} ;
      showMethod();
   }
}

你还可以将 lambda 表达式分配给Action委托实例, 如下面的示例所示。You can also assign a lambda expression to an Action delegate instance, as the following example illustrates. (有关 lambda 表达式的介绍, 请参阅Lambda 表达式。)(For an introduction to lambda expressions, see Lambda Expressions.)

using System;
using System.Windows.Forms;

public class Name
{
   private string instanceName;
   
   public Name(string name)
   {
      this.instanceName = name;
   }

   public void DisplayToConsole()
   {
      Console.WriteLine(this.instanceName);
   }

   public void DisplayToWindow()
   {
      MessageBox.Show(this.instanceName);
   }
}

public class LambdaExpression
{
   public static void Main()
   {
      Name testName = new Name("Koani");
      Action showMethod = () => testName.DisplayToWindow();
      showMethod();
   }
}
Public Class Name
   Private instanceName As String
   
   Public Sub New(name As String)
      Me.instanceName = name
   End Sub
   
   Public Function DisplayToConsole() As Integer
      Console.WriteLine(Me.instanceName)
      Return 0
   End Function
   
   Public Function DisplayToWindow() As Integer
      Return MsgBox(Me.instanceName)
   End Function      
End Class

Module LambdaExpression
   Public Sub Main()
      Dim name1 As New Name("Koani")
      Dim methodCall As Action = Sub() name1.DisplayToWindow()
      methodCall()
   End Sub
End Module

扩展方法

GetMethodInfo(Delegate) GetMethodInfo(Delegate) GetMethodInfo(Delegate) GetMethodInfo(Delegate)

获取指示指定委托表示的方法的对象。Gets an object that represents the method represented by the specified delegate.

适用于

另请参阅