[Gambas-user] Impossible to get the text property of a textbox in a for each enumeration

[Marc Guillaume]

Le Fri, 10 Sep 2021 23:17:30 +0200,
Tobias Boege via User <user at lists.gambas-basic.org> a écrit :

> On Fri, 10 Sep 2021, Marc Guillaume wrote:
> > Hello,
> > I am retrieving data from a mysql database in a gridview. I edit a
> > line with a popup menu in a form which contains the data of the
> > database. The data in the form are in textboxes associated with a
> > label and all these couples label textbox are in a panel. To be
> > able to detect if the user has modified a field I put the database
> > value in textbox1.text and textbox1.tag and so on. When closing the
> > form I want to check if the user has modified any fields. So I
> > browse the children of the panel and if the child is a textbox I
> > want to compare the text and tag values. If they are different then
> > I will know that there has been a modification and I can alert the
> > user. So I put this code in the closure processing. 
> > 
> > Public Sub btnCancel_Click()
> > 
> >   Dim iResponse As Integer
> >   Dim oChild As Control
> >   Dim bModif As Boolean = False
> > 
> >   For Each oChild In panIel1.Children 
> >     If oChild Is TextBox
> >       If oChild.text <> oChild.Tag
> >         bModif = True
> >       Endif
> >     Endif
> >   Next
> >   If bModif
> >     iResponse = Message.Warning( etc.
> > 
> > But while in the for each loop I get the value of the tag without
> > any problem I have an error for the text property : 
> > 
> > "Unknown text symbol in the control class"
> >   
> 
> In this case, it matters for property lookup which type your variable
> is declared as. You can look up the Tag property of oChild because it
> exists in the Control class, but Text does not. Even if oChild is
> really a TextBox, you declared it as merely a Control.
> 
> You can either force a dynamic symbol lookup by using
> 
>   If oChild Is TextBox Then
>     If Object.GetProperty(oChild, "Text") <> oChild.Tag Then
>       ...
> 
> or by coercing oChild into a TextBox-typed variable:
> 
>   If oChild Is TextBox Then
>     Dim tbChild As TextBox = oChild
>     If tbChild.Text <> tbChild.Tag Then
>       ...
> 
> The coercion will fail at runtime if the real class of oChild is
> incompatible with (i.e. does not derive from) TextBox, but you guard
> for that with the enclosing If ... Is TextBox.
> 
> Best,
> Tobias
> 

Thank you very much!

I thought there was a problem with classes and class inheritance but I didn't know how to access these textbox properties from the control class.

Good night!