EventArgs.Empty 字段
重要
一些信息与预发行产品相关,相应产品在发行之前可能会进行重大修改。 对于此处提供的信息,Microsoft 不作任何明示或暗示的担保。
提供要用于没有事件数据的事件的值。
public: static initonly EventArgs ^ Empty;
C#
public static readonly EventArgs Empty;
staticval mutable Empty : EventArgs
Public Shared ReadOnly Empty As EventArgs
以下示例演示一个简单的计数应用程序,该应用程序在等于或超过阈值时引发事件。 字段 Empty 将 OnThresholdReached
传递给 方法。
C#
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
将此值传递给与没有数据的事件关联的事件处理程序。
产品 | 版本 |
---|---|
.NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
.NET Framework | 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
.NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1 |
UWP | 10.0 |