Bindings for iOS

SPBindings.h

#import <Foundation/Foundation.h>

@interface NSObject (SPBindings)
-(void)sp_bind:(NSString*)binding toObject:(id)observable withKeyPath:(NSString*)observableKeyPath;
-(void)sp_unbind:(NSString*)binding;
@end

SPBindings.m

#import "SPBindings.h"

@interface SPBinding : NSObject
{
	id object;
	id observable;
	NSString *objectKeyPath;
	NSString *observableKeyPath;
}
@property (nonatomic, assign) id object;
@property (nonatomic, assign) id observable;
@property (nonatomic, copy) NSString *objectKeyPath;
@property (nonatomic, copy) NSString *observableKeyPath;
@end
@implementation SPBinding
@synthesize object, observable, objectKeyPath, observableKeyPath;
+binding;
{
	return [[[SPBinding alloc] init] autorelease];
}
-(void)dealloc;
{
	self.object = self.observable = self.objectKeyPath = self.observableKeyPath;
	[super dealloc];
}
-(NSString*)ident;
{
	return [NSString stringWithFormat:@"%x.%@", object, objectKeyPath];
}
@end



@class SPBindings;
static SPBindings *singleton = nil;

@interface SPBindings : NSObject {
	NSMutableDictionary *bindings;
}
-(void)bind:(id)obj from:(NSString*)binding toObject:(id)observable withKeyPath:(NSString*)observableKeyPath;
-(void)unbind:(id)obj from:(NSString*)binding;
@end
@implementation SPBindings
+sharedBindings;
{
	if(!singleton) singleton = [SPBindings new];
	return singleton;
}
-init;
{
	bindings = [NSMutableDictionary new];
	return self;
}
-(void)dealloc;
{
	for (SPBinding *binding in bindings)
		[self unbind:binding.object from:binding.objectKeyPath];
	
	[bindings release];
	[super dealloc];
}
-(void)bind:(id)obj from:(NSString*)objKeyPath toObject:(id)observable withKeyPath:(NSString*)observableKeyPath;
{
	SPBinding *binding = [SPBinding binding];
	binding.object = obj;
	binding.observable = observable;
	binding.objectKeyPath = objKeyPath;
	binding.observableKeyPath = observableKeyPath;
	
	SPBinding *oldBinding = [bindings objectForKey:binding.ident];
	if(oldBinding) [self unbind:oldBinding.object from:oldBinding.objectKeyPath];
	
	[bindings setObject:binding forKey:binding.ident];
	[obj addObserver:self forKeyPath:objKeyPath options:NSKeyValueObservingOptionNew context:binding];
	[observable addObserver:self forKeyPath:observableKeyPath options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionInitial context:binding];
}
-(void)unbind:(id)obj from:(NSString*)objKeyPath;
{
	SPBinding *templateBinding = [SPBinding binding];
	templateBinding.object = obj;
	templateBinding.objectKeyPath = objKeyPath;

	SPBinding *binding = [[[bindings objectForKey:templateBinding.ident] retain] autorelease];
	[bindings removeObjectForKey:templateBinding.ident];
	
	[binding.object removeObserver:self forKeyPath:binding.objectKeyPath];
	[binding.observable removeObserver:self forKeyPath:binding.observableKeyPath];
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context;
{
	SPBinding *binding = (id)context;
	
	// Update the object that this is *not* a KVO for (to mirror the value)
	id o; NSString *path;
	if(object == binding.object) {
		o = binding.observable;
		path = binding.observableKeyPath;
	} else {
		o = binding.object;
		path = binding.objectKeyPath;
	}
	
	[o removeObserver:self forKeyPath:path];
	[o setValue:[change objectForKey:NSKeyValueChangeNewKey] forKey:path];
	[o addObserver:self forKeyPath:path options:NSKeyValueObservingOptionNew context:binding];
}
@end


@implementation NSObject (SPBindings)
-(void)sp_bind:(NSString*)binding toObject:(id)observable withKeyPath:(NSString*)observableKeyPath;
{
	[[SPBindings sharedBindings] bind:self from:binding toObject:observable withKeyPath:observableKeyPath];
}
-(void)sp_unbind:(NSString*)binding;
{
	[[SPBindings sharedBindings] unbind:self from:binding];
}
@end