gistfile1.txt

#pragma mark - Undo Support

- (void)addUndoObservers
{
	for (CatalogPage *onePage in _catalog.pages)
	{
		NSArray *undoableHotZoneKeys = [CatalogPageHotZone undoableKeys];
		
		for (CatalogPageHotZone *oneHotZone in onePage.hotZones)
		{
			for (NSString *oneKey in undoableHotZoneKeys)
			{
				[oneHotZone addObserver:self forKeyPath:oneKey options:NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew context:DTCatalogDocumentUndoObservationContext];
			}
		}
	}
}

- (void)removeUndoObservers
{
	for (CatalogPage *onePage in _catalog.pages)
	{
		NSArray *undoableHotZoneKeys = [CatalogPageHotZone undoableKeys];
		
		for (CatalogPageHotZone *oneHotZone in onePage.hotZones)
		{
			for (NSString *oneKey in undoableHotZoneKeys)
			{
				[oneHotZone removeObserver:self forKeyPath:oneKey context:DTCatalogDocumentUndoObservationContext];
			}
		}
	}
}

- (void)observeForUndoValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change
{
	NSUndoManager *undoManager = [self undoManager];
	
	id oldValue = change[NSKeyValueChangeOldKey];
	
	if (oldValue == [NSNull null])
	{
		oldValue = nil;
	}
	
	[[undoManager prepareWithInvocationTarget:object] setValue:oldValue forKeyPath:keyPath];
	[undoManager setActionName:NSLocalizedString(@"Edit Hot Zone", @"Edit Action")];
}


- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
	if (context == DTCatalogDocumentUndoObservationContext)
	{
		[self observeForUndoValueForKeyPath:keyPath ofObject:object change:change];
		return;
	}
	
	if ([keyPath isEqualToString:@"selectionIndexes"])
	{
		CatalogPage *page = _catalog.pages[_arrayController.selectionIndex];
		
		_inspectorTabViewController.representedObject = page;
		
		// cannot animate or else we get exception on first swipe backwards
		[_pageController setSelectedIndex:_arrayController.selectionIndex];
	}
}