EventArgs.Empty Field

public: static initonly EventArgs ^ Empty;

public static readonly EventArgs Empty;

 staticval mutable Empty : EventArgs

Public Shared ReadOnly Empty As EventArgs 

Field Value

Examples

The following example shows a simple counting application that raises an event when a threshold is equaled or exceeded. The Empty field is passed to the OnThresholdReached method.

using System;

namespace ConsoleApplication1
{
 public class Program1
 {
 public static void Main()
 {
 Counter c = new(new Random().Next(10));
 c.ThresholdReached += c_ThresholdReached;

 Console.WriteLine("press 'a' key to increase total");
 while (Console.ReadKey(true).KeyChar == 'a')
 {
 Console.WriteLine("adding one");
 c.Add(1);
 }
 }

 static void c_ThresholdReached(object? sender, EventArgs e)
 {
 Console.WriteLine("The threshold was reached.");
 Environment.Exit(0);
 }
 }

 class Counter
 {
 private readonly int _threshold;
 private int _total;

 public Counter(int passedThreshold)
 {
 _threshold = passedThreshold;
 }

 public void Add(int x)
 {
 _total += x;
 if (_total >= _threshold)
 {
 OnThresholdReached(EventArgs.Empty);
 }
 }

 protected virtual void OnThresholdReached(EventArgs e)
 {
 ThresholdReached?.Invoke(this, e);
 }

 public event EventHandler? ThresholdReached;
 }
}

open System

type Counter(threshold) =
 let mutable total = 0

 let thresholdReached = Event<_>()

 member this.Add(x) =
 total <- total + x
 if total >= threshold then
 thresholdReached.Trigger(this, EventArgs.Empty)

 [<CLIEvent>]
 member _.ThresholdReached = thresholdReached.Publish

let c_ThresholdReached(sender, arg) =
 printfn "The threshold was reached."
 exit 0

let c = Counter(Random().Next 10)
c.ThresholdReached.Add c_ThresholdReached

printfn "press 'a' key to increase total"
while Console.ReadKey(true).KeyChar = 'a' do
 printfn "adding one"
 c.Add 1

Module Module1

 Sub Main()
 Dim c As Counter = New Counter(New Random().Next(10))
 AddHandler c.ThresholdReached, AddressOf c_ThresholdReached

 Console.WriteLine("press 'a' key to increase total")
 While Console.ReadKey(True).KeyChar = "a"
 Console.WriteLine("adding one")
 c.Add(1)
 End While
 End Sub

 Sub c_ThresholdReached(sender As Object, e As EventArgs)
 Console.WriteLine("The threshold was reached.")
 Environment.Exit(0)
 End Sub
End Module

Class Counter
 Private threshold As Integer
 Private total As Integer

 Public Sub New(passedThreshold As Integer)
 threshold = passedThreshold
 End Sub

 Public Sub Add(x As Integer)
 total = total + x
 If (total >= threshold) Then
 OnThresholdReached(EventArgs.Empty)
 End If
 End Sub

 Protected Overridable Sub OnThresholdReached(e As EventArgs)
 RaiseEvent ThresholdReached(Me, e)
 End Sub

 Public Event ThresholdReached As EventHandler
End Class

Remarks

Pass this value to event handlers that are associated with events that do not have data.

See also

• Handling and Raising Events
• How to: Raise and Consume Events
• Events (Visual Basic)
• Events (C# Programming Guide)
• Events (F#)
• Events and routed events overview (Windows store apps)