macOS Replicate Xcode's Show/Hide buttons from Top Right Corner?

[ArtOfWarfare]

My UI has several split views with sections that can be collapsed, much like Xcode's.

I'm running into several issues implementing toolbar buttons which can collapse the optional subviews, though.

1 - When you click on the toolbar buttons, they (and their background) darken, and vertical bars are added to either side of it.
2 - They don't take on a blue tint, even though they're template images.
3 - This code I found on Stack Overflow didn't do anything useful for me:

- (IBAction)toggleNavigator:(id)sender {
    [self.navigatorScroller setHidden:![self.navigatorScroller isHidden]];
    [self.verticalSplitter adjustSubviews];
}

It hides and unhides the view, but it doesn't actually expand the other view to fill the newly emptied space. Plus after doing this, dragging on the divider doesn't work.

I see that there are other answers on the question, but they look "hacky" to me, and like code that usually after I write it, I find that other, much simpler, solutions exist.

IE, I spent two hours writing complicated code for giving my split view a minimum size, but then I discovered that simply using ≥ constraints gave me the same thing in seconds instead of hours, and worked much more reliably.

Edit: Fixed #1 by dragging in a Bevel - Toggle button and having it display only an image. I'm guessing the blue tint behavior (#2) in Xcode is probably from an alternate image. I tested and I can make this toggle pretty well.

So my only remaining issue is #3...

Edit 2x: I just realized - when those buttons are pressed in Xcode, the views actually slide in and out - they don't simple appear and disappear.

Edit 3x: So... I decided to turn to objc-runtime.h since NSSplitView's clearly know a thing or two about collapsing their views, and sure enough, I turned up this private method:

_setSubview:isCollapsed:

isCollapsed presumably wants a boolean, but subview is either looking for an index or a view...

Edit 4x: I wrote this code and it works:

- (IBAction)toggleNavigator:(id)sender {
    NSMethodSignature *signature = [NSSplitView instanceMethodSignatureForSelector:@selector(_setSubview:isCollapsed:)];
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
    invocation.target = self.verticalSplitter;
    invocation.selector = @selector(_setSubview:isCollapsed:);
    [invocation setArgument:&_navigatorScroller atIndex:2];
    BOOL arg = YES;
    [invocation setArgument:&arg atIndex:3];
    [invocation invoke];
}

Now the question is... can I get away with this on the Mac App Store? Perhaps it's possible to decompile the code and replicate it as a non-private method?