Handle events for dynamic (run-time) controls - VB.NET

Question

I have a WebBrowser control that is created and added to the form during run-time.

How do I connect this control to subroutine that can handle its events at run-time?

Solution 1

Use AddHandler

e.g.

AddHandler Obj.Ev_Event, AddressOf EventHandler

and when you want to get rid of it (and you should get rid of it when you're done using it)

RemoveHandler Obj.Ev_Event, AddressOf EventHandler

in your case, you might have something like

Dim web as New WebBrowser()
AddHandler web.DocumentCompleted, AddressOf HandleDocumentCompleted

assuming you'd created an event handler called HandleDocumentCompleted

Depending on your needs, you could also use the WithEvents keyword when you declare your webbrowser; see the documentation.

Solution 2

An alternative to using AddHandler is the declarative events syntax in VB. To use it, you declare the control (as a private member), using the WithEvents keyword. Then, the Handles keyword can be used on methods to handle the appropriate events:

Private WithEvents m_WebBrowser As WebBrowser

Private Sub WebBrowser_Navigate(ByVal sender As Object, ByVal e As WebBrowserNavigatedEventArgs) Handles m_WebBrowser.Navigate
    MsgBox("Hi there")
End Sub

Private Sub SomeActionThatCreatesTheControl()
    m_WebBrowser = New WebBrowser()
End Sub

There are mainly two advantages to this method:

• No need for RemoveHandler,
• No need to wire all event handlers manually: this is done automatically.

Solution 3

• You will need to use AddHandler and RemoveHandler.
• If you manually add an event through AddHandler be sure to remove it (in an appropriate location) using RemoveHandler.
• Typing "AddHandler NameOfControl." will give a list of available events via intellisense.
• Intellisense, documentation, (or the "error list"), will also give you the "signature" of the event handler.

Private Sub WebBrowser1_Navigate(ByVal sender As Object, ByVal e As WebBrowserNavigatedEventArgs)

End Sub

Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
    RemoveHandler WebBrowser1.Navigated, AddressOf WebBrowser1_Navigate
End Sub

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    AddHandler WebBrowser1.Navigated, AddressOf WebBrowser1_Navigate        
End Sub