[JS] Event handler function is shown as the result in the ESTK

Question

I have a ScriptUI tree, with an onExpand event, like this:
Window1.tvwTree.onExpand  = function (item){
    $.writeln(item.key + " is now expanded.");
Every time the script is run, I get this in the Javascript console of the ExtendScript Toolkit:
Execution finished. Result: onExpand()
First question is: why?
Second question: What's the best and cleanest way to take care of the onExpand event? I didn't manage to assign a function to the onExpand event, in the same way as I do for parameter-less functions.
For simpler events, with no parameters, I do it like this:
Window1.....DropDownList2.onChange = cboNewLanguage_onChange;
... but the onExpand event has its "item" parameter to take care of, and I don't manage to assign the function in a similar way. Please enlighten me.
(Would it be possible to use a prototype approach, for events like this? Getting a common function for all onExpand events...???)
Thanks,
Andreas

Answer 1

Hi Andreas,
First question: what is supposed to be item.key? Have you extended the ListItem properties?
The way you assign the onExpand function seems correct to me. The following code should work:
var myExpandHandler = function(/*ListItem*/ item)
     // this => TreeView
     // item => expanded ListItem
     alert( item.text + ' is now expanded.' );
myTree.onExpand = myExpandHandler;
Alternately, you can create a generic handler through the TreeView prototype:
TreeView.prototype.onExpand = function(/*ListItem*/ item)
     // this => TreeView
     // item => expanded ListItem
     alert( item.text + ' is now expanded.' );
Works for me in CS4 & CS5+.
Note: the onExpand function has no event listener counterpart, so you cannot use the form:  <widget>.addEventListener('expand', myEventListener).
I don't know why your script causes the ESTK console to display "Result: onExpand()". Probably your code contains the corresponding $.writeln somewhere, doesn't it? Also, take into account that if your UI code uses sth like myListItem.expanded = true; then the onExpand handler is called before the win.show(). This may explain unexpected feedback in the console (?)
@+
Marc