[Gambas-user] Forward events from constructor

[Tobias Boege]

Hi,

I'm puzzled by some behaviour of the interpreter when objects raise events
from their constructors.

The following big block of text just gives the rationale of my question. I
think what I'm doing is not too strange. There is a short demonstration
project attached.

In my real project I want to implement a TextBox with a ToolButton next to
it. This thing has a Validate event and should it be Stop Event'd by the
user, this counts as invalid input. The validity of the input is reflected
by the ToolButton's Picture. The user can specify a message which is dis-
played as a Balloon over the ToolButton after the Button was clicked,
explaining why the input is invalid.

This is done in the following manner: FValidateBox is a Form class which
handles all the logic. On top of that is ValidateBox.class which keeps an
internal FValidateBox. If that FValidateBox raises its Validate event,
ValidateBox forwards it to the user and redirects any Stop Event back to
the FValidateBox to evaluate.

This works, except that I also want to force an initial validation of the
empty TextBox to initialise the ToolButton's Picture correctly (the question
is here: does the user accept the empty string?). So I write in the
constructor of ValidateBox.class:

  Inherits UserControl

  Private $frmControl As FValidateBox

  Public Sub _new()
    $frmControl = New FValidateBox(Me) As "Control"
    ' Call the Change handler of the TextBox which initiates the validation
    ' process by raising $frmControl's Validate event.
    $frmControl.txtInput_Change()
  End

I noticed that in this scenario, the event raised by $frmControl does not
reach the Control_Validate() handler in ValidateBox.class and therefore the
validation process gets a false positive "correct" answer since nobody had
a chance to Stop Event. [ As a workaround, I think I can use a Timer with
short delay, despite its ugliness. But I'm curious about the reason. ]

Is there a limitation, about raising events from constructors, I don't know
of? Also note how, in the demonstration project, I can very well initiate
the validation procedure just after the constructor finished.

Regards,
Tobi

-- 
"There's an old saying: Don't change anything... ever!" -- Mr. Monk
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