ObservableValue Stacktrace

John Hendrikx hjohn at xs4all.nl
Fri Jun 7 10:24:44 PDT 2013

Ok, I understand -- it was printed to one of the System streams directly 
(I don't configure any further logging, so I may have missed these 
warnings in the past in earlier JavaFX releases).

I have however been kinda relying on JavaFX ignoring the nulls in 
bindings -- as these are all UI related, often I will switch parts of 
the UI on/off when certain objects are not available (ie, null), but 
when they are available, then they're visible, including all their other 
bindings.  This is especially convenient when elements are loaded on 
demand, which almost everything is in my application.  When one of the 
values becomes non-null, because a background process has provided it, 
then that part of the UI becomes visible, and its values are filled.

In fact, I've further enhanced what is possible with Bindings, allowing 
for bindings to be looked up inside Maps, or even from public properties 
(like "public final StringProperty title;") with a single 
Bindings.select() style command -- for example:

   MapBindings.select(videoProperty(), "dataMap", YouTube.class, 
"rating");  // will return rating if videoProperty non-null, dataMap is 
non-null and dataMap contains key YouTube.class...

I'm kinda surprised this is not desired behaviour -- it is the Elvis 
operator (?:) of JavaFX, very convenient -- the provided default suits a 
UI's purposes probably 99% of the time (leave something blank or 0 -- if 
the UI logic doesn't simply hide it before it even gets to that point...)


On 6/06/2013 19:43, Richard Bair wrote:
> I don't think we ought to print to stdout or stderr in any case in the platform. A logger is a better idea. But really I think it is unlikely that this particular message will be that useful (it will be unhelpful in just as many cases). It is not uncommon for a chain to have a null in it at some point, and the presence of the message will just make people think something is wrong when in fact it isn't.
> Richard
> On Jun 6, 2013, at 9:31 AM, Kevin Rushforth<kevin.rushforth at oracle.com>  wrote:
>> Perhaps using the logging system would be a better choice in the case than printing to stderr?
>> -- Kevin
>> Martin Sladecek wrote:
>>> On 06/06/2013 10:53 AM, John Hendrikx wrote:
>>>> Hm, ok -- it is correct that it doesn't fail, the code runs without any problem and everything works as expected.
>>>> But, what would be the way to avoid these messages in my log then?  Something like:
>>>>   Bindings.select( Bindings.when(dataProperty().isNull()).then( ??? ).otherwise(dataProperty()), "castings") );
>>>> ??
>>>> I'd prefer to just turn these warnings off unless there is a really good reason to have them (ie, they indicate a logic error or other bug, something I can resolve...)
>>> This might indicate a logic error in many cases, esp. when the property you bind is a primitive type. When the select fails in the middle of computation, the only it can do is to set the property to default value (which is 0). If the developer
>>> didn't expect this, it would be quite hard to find the actual cause of the zero. If you really expect nulls along the way, it's much cleaner to handle this explicitly as you do in the code above.
>>>> In my case the dataProperty() is often bound to the selection of a ListView -- if you have something valid selected, then a Detail Pane is filled in with information about the selected item.  When nothing is selected (ie, it is null), then the Detail Pane should remain empty... I donot want to have to remove/recreate these bindings every time some property becomes null.
>>>> Also, it seems rather wierd that JavaFX will complain about nulls in the first part of the Bindings.select(), but will happily traverse the graph (with or without nulls) for the other parts.
>>> This is a bug then, it should print the warning in any part of the select expression.
>>> -Martin

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