Event handling

General
1

I defined one class (MyClass) with a constructor with an integer parameter (value). This is the constructor:

If value >  1000 Then
  MessageBox("not Valid")
  RaiseEvent MyEvent
Else
  MessageBox("valid")
End If

MyEvent has been defined in the Event Definition of MyClass (no parameters, no Return)

In Window1 I want to handle MyEvent in the Opening event of the Window:

Var MyObject As MyClass = New MyClass(1500)
AddHandler MyObject.MyEvent, WeakAddressof MyRemark

MyRemark is a method in Windows1 with one MessageBox.

AddHandler gives two error messages:

  1. Expected delegate Delegate(MyClass), but got delegate Delegate()
  2. This method requires fewer parameters than were passed.

I don’t understand what is wrong with this piece of code!

2

Part of the problem might be that you are instantiating MyClass (which will raise MyEvent) before you call AddHandler.

2 Likes
3

I think you wrote

If value >  1000 Then
  MessageBox("not Valid")
  RaiseEvent MyEvent
Else
  MessageBox("valid")
End If

// Calling the overridden superclass constructor.
Super.Constructor

It is preferable wrote:


// Calling the overridden superclass constructor.
Super.Constructor

If value >  1000 Then
  MessageBox("not Valid")
  RaiseEvent MyEvent
Else
  MessageBox("valid")
End If
1 Like
4

Event handler methods receive an additional parameter that refers back to the object that’s raising the event:

i.e. it should look like this:

Sub MyRemark(Sender As MyClass)

rather than like this:

Sub MyRemark()
1 Like
5

@Andrew_Lambert True, no error messages anymore. But the message in MyRemark (MessageBox(“Value not OK”)) isn’t displayed yet.

@Clifford_Antrim That’s a good advice. I will change the program not sending a value to the constructor.

@J_Luc_Pellerin I think Super.Constructor is not important in this case.

6

@Andrew_Lambert @Clifford_Antrim A combination of both replies solved the problem. Thank you so much!

Sub MyRemark(sender As MyClass)
MessageBox("Value not ok")

In the Opening event:

Var MyObject As MyClass = New MyClass
AddHandler MyObject.MyEvent, WeakAddressof MyRemark
MyObject.MyInput(1500)