help with loop on intercepting selectionChanging from TreeView

I have just attempted to intercept the #selectionChanging event from a
TreeView.  I have copied and adapted the code from the Class Hierarchy
Browser to put up a yes/no dialog if the associated'data' view has unsaved
modifications.  The net result is an infinite loop of dialog appearances,
whatever the answer given to the dialog (The 'value' of the selection
changing event is being set to the answer from the dialog).  If I comment
out just the code to put up the dialog then no looping occurs.  The Dolphin
5.0 release notes includes a reference to this problem, refering to the tree
control as being buggy in this respect.  It is not completely clear whether
the release note is highlighting the problem or implying that it has been
fixed.  As a novice when it comes to Win32 GUI programming, I am hoping I
have just missed out something 'obvious'.  Suggestions as to what this might
be would be appreciated.

Neil Dyer

Email: [hidden email]



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Neil,

> I have just attempted to intercept the #selectionChanging event from a
> TreeView.
[]

It seems to work as expected in 5.1?.  I created a Shell subclass
containing a TreeView, populated the tree, hooked onto the
#selectionChanging: event and added the following method to my
subclass...

onSelectionChanging: aValueHolder
    aValueHolder value: (MessageBox confirm: 'Allow change')

Apart from the MessageBox being displayed once before the Shell was
visible (which should be easily fixable) the tree selection was only
changed if I selected "Yes" - and I didn't get a recursive loop either.

Can you post a bit of code to show what you are doing?

--
Ian

Thanks for the feedback Ian.  I've created a similar minimal Shell subclass
in 5.1 which can be made to loop when choosing 'No' repeatedly, but performs
as you described when 'Yes' is chosen.  The looping occurs on selecting an
entry in the tree when there is no current selection in the tree (In what I
was doing, this was the only case where intercepting the change was
relevant).  Can you reproduce this behaviour?

Below is the method called on #selectionChanged: that can go into an
infinite loop when the tree has no current selection (adapted from
SmalltalkWorkspace>>prompt:toSaveChanges: ).

onPromptToSaveChanges: aSelectionChangingEvent

 aSelectionChangingEvent canIntercept ifFalse:

    ^ aSelectionChangingEvent value
   ].
 self isModified ifTrue:

    | response |
    self ensureVisible.
    response := ( MessageBox new )
    taskModal;
    owner: self view;
    confirm: ( 'There are unsaved %1 changes.%n%nDo you wish to retain
them?'
        formatWith: self descriptorClass name ).
    response ifTrue:

       self ensureVisible.
       aSelectionChangingEvent value: response not. ].
 ].
 ^ aSelectionChangingEvent value

Commenting out the send of #taskModal changes the behaviour so that the
dialog only appears one, two or three times when choosing not to retain
changes.  The dialog appears two or three times when changing to no
selection (from no selection).

Neil

"Ian Bartholomew" <[hidden email]> wrote in message
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Neil,

>  I've created a similar minimal Shell
> subclass in 5.1 which can be made to loop when choosing 'No'
> repeatedly, but performs as you described when 'Yes' is chosen.

It might be best if you mail me a copy of this minimal shell so I can
see exactly what it is that you are trying to do.  It does look as if
you have just copied too much from the original method though - a lot of
your posted code is probably not needed.  Assuming your tree contains
Objects (as opposed to Strings) then I would have thought you could just
get away with

onTreeSelectionChanging: aValueHolder
    (treePresenter hasSelection and: [treePresenter selection
isModified])
        ifFalse: [^self].
    aValueHolder value: (MessageBox confirm: 'Selection has been
modified. Continue?')

--
Ian