Docs for Binding lacking?

John Hendrikx hjohn at
Thu Jun 13 16:41:17 PDT 2013

Hi List,

I'm having a hard time to find good documentation on some aspects of 
bind and bindDirectional.  I found several forum posts, some books and 
lots of examples, but none really touch upon the subject of references 
between bindings and garbage collection.

Would it be possible to enhance the javadocs a bit or create a tutorial 
for this?  Things that are unclear for me (until I test by trail and 
error), so correct me if I got something wrong:

1) Garbage collection of bindings; basically, X.bind(Y) will result in 
X's lifecycle to be bound to Y.  If Y is a long-lived object, and X is a 
short-lived frequently replaced object, then many instances of X will be 
left around consuming memory (and CPU cycles on every Y update) until Y 
dies.  A single forgotten binding of this type can result in whole UI 
graphs to be locked in memory.

The same does not occur with bindBidirectional. The javadocs describe 
this type of binding as "bind with inverse", which sounds to me it is 
mere short-hand for doing X.bind(Y) + Y.bind(X), if that were allowed, 
resulting in both X and Y's lifecycles to be bound to each other.  Yet, 
that's not what happens.  With a bidirectional binding, either X or Y 
can go out of scope, and the binding dies with it, which is a very nice 
feature and an important consideration when choosing the type of binding 
that it deserves some mention in the docs.

Using bind() seems to be the default that is used everywhere, because it 
is short and nice -- I'm however thinking my life would have been much 
easier had I used bindBidirectional as the "default" binding everywhere 
in my code -- I'm pretty sure most of the bindings I did in the past 
could have been bidirectional without any consequence. In complex cases 
with many unidirectional bindings (that maybe could have been 
bidirectional without impacting the result), I resorted to using a 
helper class that keeps track of all the bindings created so they can 
all be unbound with a single call to avoid creating somekind of memory leak.

2) For bi directional bindings, it is unclear which value will be the 
final result of the two bound properties (especially confusing in 
Bindings.bindBidirectional).  X.bind(Y) will mean X takes the value of Y 
as the direction of the binding enforces it.  X.bindBidirectional(Y) or 
Bindings.bindBidirectional(X, Y) have no direction and it is unclear 
whether, initially, the result will be the value of X or the value of Y.


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