in iOS7, with Titanium, if you set rightNavButton or leftNavButton, with a custom button or view.. etc, it has extra spacing on the left or right side, which is really annoying, if you want the button snap to the edge. here is a small hack, if you need the view positioned to the left or right side correctly.

TiUIWindowProxy.m

//from line 502

-(void)setRightNavButton:(id)proxy withObject:(id)properties
{
	ENSURE_UI_THREAD_WITH_OBJ(setRightNavButton,proxy,properties);
    if (properties == nil) {
        properties = [self valueForKey:@"rightNavSettings"];
    }
    else {
        [self setValue:properties forKey:@"rightNavSettings"];
    }
	
	if (controller!=nil && 
		[controller navigationController] != nil)
	{
		ENSURE_TYPE_OR_NIL(proxy,TiViewProxy);
		[self replaceValue:proxy forKey:@"rightNavButton" notification:NO];
		if (proxy==nil || [proxy supportsNavBarPositioning])
		{
			// detach existing one
			UIBarButtonItem *item = controller.navigationItem.rightBarButtonItem;
			if ([item respondsToSelector:@selector(proxy)])
			{
				TiViewProxy* p = (TiViewProxy*)[item performSelector:@selector(proxy)];
				[p removeBarButtonView];
			}
			if (proxy!=nil)
			{
				// add the new one
                BOOL animated = [TiUtils boolValue:@"animated" properties:properties def:NO];
                
                //only ios7+ and if the view has the value set
                if([proxy valueForKey:@"rightNavNegativeSpace"] != nil && [TiUtils isIOS7OrGreater]){
                    
                    UIBarButtonItem *negativeSpacer = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
                    negativeSpacer.width = [[proxy valueForKey:@"rightNavNegativeSpace"] floatValue];
                    
                    [controller.navigationItem setRightBarButtonItems:[NSArray arrayWithObjects:negativeSpacer, [proxy barButtonItem], nil] animated:animated];
                
                } else{
                    
                    [controller.navigationItem setRightBarButtonItem:[proxy barButtonItem] animated:animated];
                    
                }
                
                
               }
			else 
			{
				controller.navigationItem.rightBarButtonItem = nil;
			}
		}
		else
		{
			NSString *msg = [NSString stringWithFormat:@"%@ doesn't support positioning on the nav bar",proxy];
			THROW_INVALID_ARG(msg);
		}
	}
	else 
	{
		[self replaceValue:[[[TiComplexValue alloc] initWithValue:proxy properties:properties] autorelease] forKey:@"rightNavButton" notification:NO];
	}
}

-(void)setLeftNavButton:(id)proxy withObject:(id)properties
{
	ENSURE_UI_THREAD_WITH_OBJ(setLeftNavButton,proxy,properties);
    if (properties == nil) {
        properties = [self valueForKey:@"leftNavSettings"];
    }
    else {
        [self setValue:properties forKey:@"leftNavSettings"];
    }
    
	if (controller!=nil && [controller navigationController] != nil)
	{
		ENSURE_TYPE_OR_NIL(proxy,TiViewProxy);
		[self replaceValue:proxy forKey:@"leftNavButton" notification:NO];
		if (proxy==nil || [proxy supportsNavBarPositioning])
		{
			// detach existing one
			UIBarButtonItem *item = controller.navigationItem.leftBarButtonItem;
			if ([item respondsToSelector:@selector(proxy)])
			{
				TiViewProxy* p = (TiViewProxy*)[item performSelector:@selector(proxy)];
				[p removeBarButtonView];
			}
			controller.navigationItem.leftBarButtonItem = nil;			
			if (proxy!=nil)
			{
				// add the new one
                BOOL animated = [TiUtils boolValue:@"animated" properties:properties def:NO];
                
                if([proxy valueForKey:@"leftNavNegativeSpace"] != nil && [TiUtils isIOS7OrGreater]){
                    
                    UIBarButtonItem *negativeSpacer = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
                    negativeSpacer.width = [[proxy valueForKey:@"leftNavNegativeSpace"] floatValue];
                    
                    [controller.navigationItem setLeftBarButtonItems:[NSArray arrayWithObjects:negativeSpacer, [proxy barButtonItem], nil] animated:animated];
                    
                } else{
                    
                    [controller.navigationItem setLeftBarButtonItem:[proxy barButtonItem] animated:animated];
                    
                }
                
            }
			else 
			{
				controller.navigationItem.leftBarButtonItem = nil;
			}
		}
		else
		{
			NSString *msg = [NSString stringWithFormat:@"%@ doesn't support positioning on the nav bar",proxy];
			THROW_INVALID_ARG(msg);
		}
	}
	else
	{
		[self replaceValue:[[[TiComplexValue alloc] initWithValue:proxy properties:properties] autorelease] forKey:@"leftNavButton" notification:NO];
	}
}

your.js

//if you put a custom view/button/etc into rightNavButton, set rightNavNegativeSpace (if right side, obviously left for leftside)
//correct spacing is -16, both side

var rightView = $.UI.create('View', {
	classes : "rightview",
	rightNavNegativeSpace : -16
});

$.win.rightNavButton = rightView;

Titanium has two ways to add buttons to the navigation bar: the leftNavButton and leftNavButtons (the second one takes an array of views). Will your solution work in this last case too?