有没有办法在VB.NET中知道一个处理程序是否已经注册了一个事件？ [英] Is there a way to know in VB.NET if a handler has been registered for an event?

问题描述

在C＃中，我可以测试这个...

In C# I can test for this...

public event EventHandler Trigger;
protected void OnTrigger(EventArgs e)
{
    if (Trigger != null)
        Trigger(this, e);
}

有没有办法在VB.NET中执行此操作？测试为null我的意思是？

Is there a way to do this in VB.NET? Test for null I mean?

更多信息

我忘了提及。我有C＃编写的课程，但我在VB.NET中编写单元测试。

I forgot to mention. I have classes written in C# but I am writing my unit tests in VB.NET.

我正在单元测试中尝试这个...

I am trying this in the unit test...

If myObject.Trigger IsNot Nothing Then  
    ''#do something
End If

这是导致编译时错误，它说...公共事件触发器是一个事件，不能被直接调用。使用RaiseEvent语句来引发事件。

This is causing a compile time error which says ... "Public Event Trigger is an Event and cannot be called directly. Use the RaiseEvent statement to raise an event."

Seth

推荐答案

有一个有趣的讨论 1129517 在C＃中如何做这个事情。

There is an interesting discussion in question 1129517 around how to do this very thing in C#.

由于包含事件的类是用C＃编写的，委托语义将适用，这些技术应该适用于您。但是，您需要将源转换为VB.NET进行单元测试。

Since the class that contains the Event was written in C#, the delegate semantics do apply, and those techniques should work for you. However, you'll need to translate the source to VB.NET for your unit test.

给定C＃程序集中的以下类：

Given the following class in a C# assembly:

public class Triggerific
{
    public event EventHandler Trigger;

    private static void OnTriggerTriggered(object sender, EventArgs e)
    {
        Console.WriteLine("Triggered!");
    }

    public void AddTrigger()
    {
        Trigger += OnTriggerTriggered;
    }
}

这是一些VB.NET代码，将正确确定如果为Trigger事件注册了一个处理程序：

Here is some VB.NET code which will correctly determine if a handler was registered for the Trigger event:

<TestMethod()> _
Public Sub TriggerTest()
    Dim cut As New Triggerific
    cut.AddTrigger()

    Assert.IsNotNull(GetEventHandler(cut, "Trigger"))
End Sub

Private Shared Function GetEventHandler(ByVal classInstance As Object, ByVal eventName As String) As EventHandler
    Dim classType As Type = classInstance.[GetType]()
    Dim eventField As FieldInfo = classType.GetField(eventName, BindingFlags.GetField Or BindingFlags.NonPublic Or BindingFlags.Instance)

    Dim eventDelegate As EventHandler = DirectCast(eventField.GetValue(classInstance), EventHandler)

    ' eventDelegate will be null/Nothing if no listeners are attached to the event
    Return eventDelegate
End Function

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