Hi,
Thanks to TJ answer, I forgot THE each second argument to
automatically bind the called function to a context.
--
david.
On 4 déc, 12:22, "T.J. Crowder" <t...@crowdersoftware.com> wrote:
> Hi,
>
> > Tracing through the code, everything appears fine up to the point
> > where I try to call the stored callback. This line:
>
> > info.key.info.value(this));
>
> > info.key and info.value are both valid objects, but nothing happens.
>
> Your 'info.key' property is your observer, which I tend to suspect
> doesn't then have a property called 'info' on it, but that's what
> "info.key.info" retrieves. Then you retrieve the 'value' property from
> that and try to call it ("info.key.info.value(this)"). You're also
> passing in a 'this' value which refers to the browser window, whereas
> I suspect you wanted to refer to the observable object.
>
> I think this is what you meant:
>
> observerInfo.each(function(info) {
> info.value.call(info.key, this);
> }, this);
>
> ...which will call the callback setting the observer as the context
> (the 'this' value within the callback) and passing in the observed
> object -- note that to do that, I had to pass 'this' into #each as its
> second argument because otherwise context is lost when you call #each.
>
> But the above, by itself, won't solve the problems because I think you
> probably have an issue here:
>
> > this.observableChanges.get(property).set(observer, callback);
>
> Hash#set is documented as accepting a String for the key, but you're
> passing in other kinds of objects, not just strings. You can't rely on
> the key not getting converted to a string (a string that will probably
> be "[Object]" or similar).
>
> FWIW, I probably wouldn't use Hash for this at all, it's overkill for
> the 'observableChanges' property and mis-matched for the values within
> that. I'd probably just use a plain JavaScript object for
> 'observableChanges' using the property name as the key, with the value
> being an array of tuples for the callbacks to make.
>
> HTH,
> --
> T.J. Crowder
> Independent Software Consultant
> tj / crowder software / comwww.crowdersoftware.com
>
> On Dec 3, 9:00 pm, Wil <wil.tur...@gmail.com> wrote:
>
> > Hi all,
>
> > I'm trying to implement a somewhat generic way for my controller
> > objects to listen for changes to various properties of my model
> > objects. I'm not a javascript expert, so there is quite possibly a
> > Better Way™ of solving the bigger problem - I'm open to pointers in
> > that direction, if my current approach is not a good idea.
>
> > Here's the machinery I currently have in place:
>
> > MyClass.prototype.observeValueChange = function(observer, property,
> > callback) {
> > if (this.observableChanges == null) this.observableChanges = new
> > Hash();
> > if (this.observableChanges.get(property) == null)
> > this.observableChanges.set(property, new Hash());
> > this.observableChanges.get(property).set(observer, callback);
>
> > }
>
> > MyClass.prototype.fireValueChanged = function(property) {
> > if (this.observableChanges == null) return;
> > var observerInfo = this.observableChanges.get(property);
> > if (observerInfo == null) return;
> > observerInfo.each(function(info) {
> > info.key.info.value(this));
> > });
>
> > }
>
> > Here's an example of registering to listen:
>
> > objectOfMyObservableClass.observeValueChange(this, 'foo', function
> > (destination) {
> > alert("observed change in foo");
>
> > });
>
> > objectOfMyObservableClass.fireValueChanged("foo");
>
> > Tracing through the code, everything appears fine up to the point
> > where I try to call the stored callback. This line:
>
> > info.key.info.value(this));
>
> > info.key and info.value are both valid objects, but nothing happens.
>
> > Thanks in advance!
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