I hope people don't mind me posting this bit of code to the list, but I hope it
will be of some use to others and would also be interested to hear if the
technique has any problems which I've not foreseen.
Ruby has its own means of implementing the observer pattern, but as Key Value
Observing (KVO) is so pervasive in cocoa, it would be good if it was easy to
use. The module is an attempt at making KVO a bit more pleasant to use in
macruby.
The ideas have been adapted/stolen from here:
https://gist.github.com/153676
The following is an example of how to have a block of code executed
asynchronously every time a property of an instance variable changes
self.add_observer_for_key_path('person.first_name', async:true) do
|object,change|
object.do_expensive_calculation #will not block main thread
end
A concern I do have is that the object which wants to receive KVO notifications
holds an array of Observer objects. These Observer objects hold a reference to
the object receiving the KVO notifications. Is this going to cause havoc with
garbage collection?
module KVO
class Observer
require 'dispatch'
attr_reader :observee, :path
def initialize(object, path, async, block, opts=0)
@observee = object
@path = path
@async = async
@block = block
@observee.addObserver(self, forKeyPath:path, options:opts, context:nil)
end
def observeValueForKeyPath(path, ofObject:object, change:change,
context:context)
if @async
Dispatch::Job.new { @block.call(object, change) }
else
@block.call(object, change)
end
end
def cancel_observation
@observee.removeObserver(self, forKeyPath:@path)
end
end
def add_observer_for_key_path(path, async:async, &block)
(@_observers_array_ ||= []) << Observer.new(self, path, async, block)
end
def add_observer_for_key_path(path, async:async, options:opts, &block)
(@_observers_array_ ||= []) << Observer.new(self, path, async, block, opts)
end
def remove_observer_for_key_path(path)
observer = @_observers_array_.find {|o| o.path == path && o.observee ==
self} if @_observers_array_
@_observers_array_.delete(observer) and observer.cancel_observation if
observer
end
end_______________________________________________
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