Re: KVO and the observeValueForKeyPath bottleneck
Re: KVO and the observeValueForKeyPath bottleneck
- Subject: Re: KVO and the observeValueForKeyPath bottleneck
- From: Aaron Burghardt <email@hidden>
- Date: Sat, 15 Jul 2006 16:56:48 -0400
On Jul 14, 2006, at 1:44 PM, Matt Neuburg wrote:
I'm just curious about how people are handling the fact that when
you do
KVO, all your notifications are bottlenecked through a single method,
observeValueForKeyPath:... This is a very unpleasant and crude
architecture
(in contrast to NSNotification where, when a notification comes in,
it is
automatically routed to the selector of your choice). I really
don't want a
series of "ifs" here. I can imagine a simple dispatcher
architecture based
on NSSelectorFromString; is this the sort of thing people are
using? Thx -
m.
--
Good question; I hope this sparks more discussion.
I can think of two approaches using the context parameter, one of
which I implemented recently. In my main controller I am observing
several array controllers, where the content object types vary from
controller to controller. When the selection on any controller
changes, I get the path to a file and display it in a viewer. When
registering as an observer, I set the context to a string constant
for the key path to the file name. Here is a simplified example:
-(void)awakeFromNib
{
[inputFilesArrayController addObserver:self forKeyPath:@"selection"
options:nil context:@"selection.sourceFilePath"];
[processedFilesArrayController addObserver:self
forKeyPath:@"selection" options:nil context:@"selection.savedToPath"];
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)
object change:(NSDictionary *)change context:(void *)context
{
// In awakeFromNib:, KVO registration done with context set to the
key value to retrieve.
// If it is a string (thus a path), then display it.
if (context) {
id displayPath = [object valueForKeyPath:context];
// We may get an placeholder marker or nil
if (displayPath && [displayPath isKindOfClass:[NSString class]]) {
[fileViewerController open:displayPath];
}
}
}
This worked OK for the given situation. If I had a more complex
scenario, I would consider enumerating constants to use as the
context and then use a switch() in observeValueForKeyPath:.
Something like this:
-(void)awakeFromNib
{
[firstArrayController addObserver:self
forKeyPath:@"selection.attribute" options:nil context:EnumConstant1];
[secondArrayController addObserver:self
forKeyPath:@"selection.attribute" options:nil context:EnumConstant2];
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)
object change:(NSDictionary *)change context:(void *)context
{
switch (context) {
case EnumConstant1:
// ...do something...
break;
case EnumConstant2:
// ...do something else...
break;
default:
break;
}
}
I haven't tried the second example, so it may not be as suitable as I
think. Comments?
Cheers,
Aaron
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