Hi all,
I love KV until I start using key paths
I have a top level object, KVC compliant, which is hooked to an
NSController in IB. I have some text fields set to the object's
values. Everything works fine, I can receive changes made to the text
fields and also set the text fields' value by invoking accessor
methods from the top object.
I have a KVC compliant object in this top level object and have set
key paths in other text fields to values in this object. I can
receive changes from the text fields, but changing its values with
accessor methods, either from the object itself, or from the top
object, doesn't register a change.
Examples:
[self setTempSetpoint:135];// this sets the bound text fields value
and sets the value in the object
[[self polCurve] setDwell:3.9]; // this doesn't, but it sets the
value in the object
[self setValue:[NSNumber numberWithFloat:3.14]
forKeyPath:@"polCurve.dwell"]; // this has the same effect as the
previous command
any help, much appreciated.
Dave
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Feb 1, 2007, at 1:10 PM, Stephen Deken wrote:

>[[self polCurve] setDwell:3.9];
>[self setValue:[NSNumber numberWithFloat:3.9]
>forKeyPath:@"polCurve.dwell"];
>
These two methods do the exact same thing, so it's not surprising that
they're both failing in the same way. What does your -[setDwell:]
function look like? It should look something like this:

-(void) setDwell:(float)v
{
[self willChangeValueForKey:@"dwell"];
_dwell = v;
[self didChangeValueForKey:@"dwell"];
}

If you leave off the will/didChangeValueForKey parts, KV doesn't know
the value has changed and won't update any bound objects.

This is incorrect. Calling -setFoo: will always trigger a binding
that is bound to the "foo" key. The will/didChange pair is only
required if you directly change the variable, or if you change
something else that the bound key relies on. They can also be used to
trigger the binding without calling the -setXXX: method.

Glen

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Feb 2, 2007, at 3:27 AM, Dave Sopchak wrote:

Also, I don't put the willChangeValueForKey stuff in my top object
and yet things work just fine in the text fields. Is this because
of the NSController attached to the top object is handling
such things?

Possible.

You rethink about what KV is which is to observe a single object's
properties/values. If I understand this correct, you have object A
which uses object B. You register to observe values in object A, so A
only knows about changes in itself. You have not registered with
object B to observe any of its values. So, if you want A to notify
clients of changes in values in B you need to add accessors to A that
forward the messages to B. Another way would be to have A observe B
and have object A's observing method call willChangeValueForKey/
didChangeValueForKey for your @"polCurve.dwell" key path. Also, it
would have help to see a sample of the code your calling as opposed
to the code which calls it. (We all know how to call accessors, so
there is not much to see there.)

Regards,
Brian Smith
http://www.suaveware.com

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Hi,
Thanks to all who have given me their input.

It seems I don't have (or don't know of) a way to notify the
NSController attached to my top object of changes to my bottom
object.

All of my code, both the callers and the accessors, are boring
vanilla types. Accessors look like this:
- (PolarizationCurve *)polCurve
{
return polCurve;
}
- (void)setPolCurve:(PolarizationCurve *)foo
{
PolarizationCurve *old = polCurve;
polCurve = foo;
[polCurve retain];
[old release];
}

- (float)anodeSetpoint
{
return anodeSetpoint;
}
- (void)setAnodeSetpoint :(float)foo
{
anodeSetpoint = foo;
}

I added registerA and observeValueForKeyPath methods to my
top object to observe the bottom object, and the
observeValueForKeyPath does get called when I hit one of the accessor
methods in the bottom object.

thing that I cannot figure out how to do is to then ping the
NSController that a change was made.

I'd be happy to supply more detailany and all help, much
appreciated. I want to script this app and I don't think that setting
values will be a problem, but not being able to get them may pose a
problem.

Dave

Feb 1, 2007, at 1:19 PM, Brian Smith wrote:

Feb 2, 2007, at 3:27 AM, Dave Sopchak wrote:
>
>>
>Also, I don't put the willChangeValueForKey stuff in my top object
>and yet things work just fine in the text fields. Is this because
>of the NSController attached to the top object is handling
>such things?
>>
>
Possible.

You rethink about what KV is which is to observe a single object's
properties/values. If I understand this correct, you have object A
which uses object B. You register to observe values in object A, so
A only knows about changes in itself. You have not registered with
object B to observe any of its values. So, if you want A to notify
clients of changes in values in B you need to add accessors to A
that forward the messages to B. Another way would be to have A
observe B and have object A's observing method call
for your
@"polCurve.dwell" key path. Also, it would have help to see a
sample of the code your calling as opposed to the code which calls
it. (We all know how to call accessors, so there is not much to
see there.)

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