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Editor to share with you how to use VB.NET WithEvents, I hope you will get something after reading this article. Let's discuss it together.

VB.NET after a long period of development, many users are very familiar with VB.NET WithEvents, here I would like to publish a personal understanding, and discuss with you. In addition to handling event responses in the same way as C#, VB also has a unique way of handling events inherited from VB5-VB.NET WithEvents.

I like to call this event handling static event handling. When you write a method that responds to an event, you already decide which event the method is responding to, while C# binds the event in the code. For example, here is the simplest example:

Public Class HandlerClass Public WithEvents MyObj As EventClass Private Sub MyObj_MyEvent (ByVal sender As Object, ByVal e As System.EventArgs) Handles MyObj.MyEvent MsgBox ("hello") End Sub Public Sub New () MyObj = New EventClass End Sub End Class

The EventClass used in the code looks like this:

Public Class EventClass Public Event MyEvent As EventHandler Protected Overridable Sub OnMyEvent (ByVal e As EventArgs) RaiseEvent MyEvent (Me, e) End Sub Public Sub Test () OnMyEvent (New EventArgs) End Sub End Class

Let's review that this code implicitly writes two methods for EventClass-Add_MyEvent (EventHandler) and Remove_MyEvent (EventHandler). Virtually any context that uses an event binds and unbinds the event by calling these two methods. C # also allows you to write your own event binding / unbinding code.

So how does WithEvents work? The compiler of VB.net automatically sets the

Public WithEvents MyObj As EventClass

Translated into the following process:

Private _ MyObj As EventClass Public Property MyObj () As EventClass Get Return _ MyObj End Get Set (ByVal Value As EventClass) If Not (Me._MyObj Is Nothing) Then RemoveHandler _ MyObj.MyEvent, AddressOf MyObj_MyEvent End If Me._MyObj = Value If Me._MyObj Is Nothing Then Exit Property AddHandler _ MyObj.MyEvent, AddressOf MyObj_MyEvent End Set End Property

Thus, when you assign a value to the VB.NET WithEvents variable, this property is automatically triggered to bind the event. Most of the event responses we use are 1-to-1, that is, a process responds to an event, so this VB.NET WithEvents static method is very useful, which can significantly enhance the readability of the code, while also making event handling in VB.net very convenient, unlike C #, which has to bind events manually without the form designer.

However, when analyzing this piece of IL, I also found a small problem with VB.net in translation, that is, there are too many ldarg.0, which is a sign of frequent use of Me or this, so we must pay attention to the coding process, in addition to using the reference of Me/this itself, do not bring Me/this when using its members, for example, change Me.MyInt = 1 to MyInt = 1. Such a small habit will bring you a lot of performance benefits.

After reading this article, I believe you have a certain understanding of "how to use VB.NET WithEvents". If you want to know more about it, you are welcome to follow the industry information channel. Thank you for reading!

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