XR2021R2 exception when setting webListBox.columncount

using the same project that I use in the xojo 2021r1.1 release and that in this release does not raise these exceptions, in the latest version of xojo, when I go to set the columnCont of a webListBox (in any part of the code) I get an exception “UnsupportedOperationException”, Message: “WebListbox.ColumnCount must be set before the Opening event finishes.”, reason: “WebListbox.ColumnCount must be set before the Opening event finishes.”

I of course need to set the number of columns dynamically, does anyone have any suggestions on how to handle this exception?

ColumnCount cannot be set at runtime now, if memory serves. You’d need to build your own ListBox implementation using WebContainers or a JavaScript component like GraffitiGrid.

I didn’t understand, it is no longer possible to set the number of columns of a webListBox dynamically? and why ? and where is it documented that at runtime it is not possible to change the number of columns of a webListBox? But then why wasn’t an exception thrown in the previous xojo release? (sorry for the impetuousness but it seems to me that xojo is creating complications instead of simplifying)

From the Release Notes:

WebListBox now raises an UnsupportedOperationException when trying to change the ColumnCount after the Opening event.

Feedback Case 65007:

And I’ve just opened a new Feedback Case to have the documentation updated:

sorry, I tried to look at case 65007 but with the feedback app I can’t see its content, also I see that the status is fixed. However, you have been told that the problem will not be solved and that the webListBox must have the number of columns statically defined ??

Ah, it’s marked as a Testers case. @Greg_O_Lone said:

Changing the column count at runtime is not currently supported.

Here is the original report:

ok, this is a paradox, they produce updates and in fact they produce huge bugs, the decline is embarrassing.

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Well, my assumption is that the underlying library has some issue with changing the columns while data is loaded. It’s not great fun, but when using open source you sometimes have these limitations or bugs that need to be sorted out upstream. Even if you build a pull request, you often don’t want to deploy it until it’s been accepted and merged for fear that it may not be in the next version you try to move to.

It looks like this particular issue is due to DataTables requiring that the entire table be destroyed and reinitialized when you want to add or remove columns and would not be an insignificant amount of work to fix because they likely cache all sorts of values that are calculated on init that are not recalculated.

For reference: how to refresh table after adding columns — DataTables forums

I change the number of columns always and only after removing all the rows of the weblistbox, which among other things, I fill by hand with data coming from rowSource, so what you indicate is not my case.

however, in the 2021r1.1 release the webListBox worked (with a lot of serious problems but it worked). With the release of this version the problems that already existed have worsened, and the webListBox is not a little used component, I think it is the one most present after the webTextBoxes. Now, I think they are going the wrong way, and I don’t even want to mention the fact that porting projects from 2019 to a> = 2020 release IS SO IMPOSSIBLE !!

it seems to me that they are missing the point.

I wish there was something more I could tell you. It seems that changing columns at runtime caused significant enough issues that the Xojo team felt it necessary to follow the guidance of the library’s developer and not attempt it.

As to the other issues you mention, I know that they are working diligently to correct as much as possible with each release. There’s really nothing more that anyone can say than that.

Maybe one option you could try is to create a WeblistBox at design time with enough columns ( say 10)
And as you requires, hide the unused columns ( eg to use 7 columns only, hide column 8 , 9 , 10)
You could use this code ( which was written by Anthony previously, i think) to hide the column
in Xojo2021R2

Session.ExecuteJavaScript( “$(’#” + lbData.ControlID + “_table’).DataTable().column(” + index.ToString( “#” ) + “).visible(” + value.ToString.Lowercase + “);” )

lbData is the WeblistBox controlID
Put it in a method ( eg: ShowColumn (Index as Integer, Value as boolean) )

It should work. To make it easier you could even try to use extension method to simplify it.


Original post:

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You must use the WebListBox Opening event instead of the WebPage Opening event when setting columns up by code.

ok, but I have to manage the number of columns dynamically, so what you indicate is not for me and does not solve the problem of the webListBox.

This is a major regression for me - the only way to change columnCount is to do it in the Opening event of the WebListBox control (you can’t even do it in the WebPage Opening event).

Why was this feature removed? It seemed to work fine before…

I explained above and included the reference on the DataTables (which the WebListBox is based on) forums with the explanation.

Per user allan on DataTables forum:

You need to destroy a table (destroy()) before you can add or remove columns.