Invoking a Method with arguments? [Resolved]

[mendhak]

When calling InvokeMethod, one can simply do:

Dim p() As Object = {"your ugly mother", 0}
        InvokeMethod(Me, "Button1_Click", p)

Now, Button1_Click takes two arguments:

sender of type System.Object,
e of type System.EventArgs

Which maps to where? Can someone explains what happens to "your ugly mother" and 0 when the Invoke method gets called?

[Asgorath]

Hi

I never use InvokeMethod to call a button_click inside another button_click and i do that a lot.

Call Button1_Click(sender, e) i leave the call just for readabilility buts its not really necessary..

Regards
Jorge

[mendhak]

Originally posted by Asgorath


I never use InvokeMethod to call a button_click inside another button_click and i do that a lot.

Call Button1_Click(sender, e) i leave the call just for readabilility buts its not really necessary..

I would do that, except I'm working to automate an app which has unknowns. Basically, any method could be invoked, so I need to work with this.

[Merrion]

You should get a runtime error because the argument type have to match the method signature i.e.

Dim p() As Object = {Me, New MouseEventArgs( MouseButtons.Left,  _ 
1, _ 
1, _ 
1, _ 
0 ) }

[mendhak]

MouseEventArgs would be applicable to all click events, am I correct?

[CyberHawke]

Yes, you are correct, anytime a mouse button is clicked, it generates a MouseClickEventArgs that is passed to the subsequent mouse click event.

Have you considered using delegates with the invoke method?

[mendhak]

I'm first trying to clear my delegate concepts.

Are you talking about something like this?

Private Sub InvokeMethod(ByVal f As Form, ByVal MethodName As String, ByRef parms() As Object)
        Dim eh As EventHandler = CType(System.Delegate.CreateDelegate(GetType(EventHandler), f, MethodName), EventHandler)
 
        If Not (eh Is Nothing) Then
            f.Invoke(eh, parms)
        End If
 
    End Sub

?

[CyberHawke]

Yes, you have that part correct, and actually, based on what I have read from these few posts, everything should work, is there a problem that I am not seeing?

[mendhak]

Yes, everything's working.

I'm just looking to understand this better. In the form of detailed descriptions or better yet, useful, descriptive links.

[CyberHawke]

ok, in your original post you listed some code and posed the question

Which maps to where? Can someone explains what happens to "your ugly mother" and 0 when the Invoke method gets called?

In your InvokeMethod method, you are taking the parms and passing them as arguments to the method you are calling in the f.Invoke method call.

The .NET framework will attempt to use the parameters supplied to invoke the method you are calling with the MethodName parameter.

For example, suppose you called "Button1_Click" as your named method, when the framework attempts to invoke that method, it is expecting arguments of types Object, and EventArgs, and the values you pass in must match that signature or the Invocation will fail.

Because of the argument types you listed, "Your ugly mother" and 0 do not match the expected signature of Object and EventArgs (well actually just the EventArgs), that the method is calling, your call will fail.

I hope that this is making sense, I am sort of rambling on.

[mendhak]

That makes sense. So this means I can declare P to be

Dim p() As Object = {Me, New EventArgs}

And pass it, and it'd work.

Very good.

[Merrion]

I think EventArgs is a MustInherit class...?

[mendhak]

Doesn't seem to be the case here... Framework 1.1, VS 2003.

[Merrion]

You're right - it is not MustInherit, but...

This class contains no event data; it is used by events that do not pass state information to an event handler when an event is raised. If the event handler requires state information, the application must derive a class from this class to hold the data.

[mendhak]

In English, that would mean:

If I have an event called StrangeThingsDone which accepts a lone string as an argument, when invoking the method handling it, I'd have to first inherit from EventArgs, (call it StrangeArgs), and then pass StrangeArgs to StrangeThings.

I know I'm repeating what's being said, just need to make sure I have all that is correct, good and holy.

[CyberHawke]

Yes, you are correct, if you want to pass information such as a string to an event handler, then you should create a class "CustomEventArgs" that has a string property, instantiate a new instance of that class, populate the string property, and then pass it as the argument to your event. I have a lot of examples for this if you are interested.

[mendhak]

Originally posted by CyberHawke
I have a lot of examples for this if you are interested.

Although I believe I have understood the concept, give me one or two examples. Also, where did you get "a lot of examples" from?

[CyberHawke]

I wrote them, I do a lot of work with Remoting and the only way to pass arguments from a server to a client, over a Remoting channel is to create a custom event args class, make it serializable and pass it as an argument.
Here are two examples of custom event args classes:

<Serializable()> _
    Public Class CustomEventArgs
        Inherits EventArgs
        Protected _eventSource As String
        Protected _pbCancel As Boolean
 
        Public Sub New(ByVal eventSource As String, ByVal cancel As Boolean)
            _eventSource = eventSource
            _pbCancel = cancel
        End Sub
 
        Public ReadOnly Property EventSource() As String
            Get
                Return _eventSource
            End Get
        End Property
 
        Public ReadOnly Property Cancel() As Boolean
            Get
                Return _pbCancel
            End Get
        End Property
    End Class

and

<Serializable()> _
    Public Class ProgressEventArgs
        Protected _eventSource As String
        Protected _progressDescription As String
        Protected _percentComplete As Int16
        Protected _progressCountLow As String
        Protected _progressCountHigh As String
 
        Public Sub New(ByVal eventSource As String, ByVal progressDescription As String, ByVal percentComplete As Int16, ByVal progressCountLow As Int16, ByVal progressCountHigh As Int16)
            _eventSource = eventSource
            _progressDescription = progressDescription
            _percentComplete = percentComplete
            _progressCountLow = progressCountLow
            _progressCountHigh = progressCountHigh
        End Sub
 
        Public ReadOnly Property EventSource() As String
            Get
                Return _eventSource
            End Get
        End Property
 
        Public ReadOnly Property ProgressDescription() As String
            Get
                Return _progressDescription
            End Get
        End Property
 
        Public ReadOnly Property PercentComplete() As Int16
            Get
                Return _percentComplete
            End Get
        End Property
 
        Public ReadOnly Property ProgressCountLow() As Int16
            Get
                Return _progressCountLow
            End Get
        End Property
 
        Public ReadOnly Property ProgressCountHigh() As Int16
            Get
                Return _progressCountHigh
            End Get
        End Property
    End Class

event declarations with the custom args:

Public Event Progress(ByVal sender As Object, ByVal args As ProgressEventArgs) Implements IJobServer.Progress
        Public Event Start(ByVal sender As Object, ByVal args As CustomEventArgs) Implements IJobServer.Start

Unfortunately, the project that I pulled these examples from use an invoke methodology instead of just raising the event, this is because multiple clients can subscribe to the events and if one dies, the server can test to see if it is still alive. If the server finds that a client has died, it can remove that clients subscription to the event. While this is cool code, it's not really applicable to your current situation and I'd rather not muck up what you are currently working on.

[mendhak]

But that's good enough. Thanks for the examples,things are clearer now.