Zoom image in a NSScrollView in objective-c

I have two NSScrollView's with scroll synchronized with each other (using Apple's example) and it is working. Next I implemented a zoom that would zoom both images (they have the same size by definition). The code for the zoom was adapted using code from here, which I present here:

    if (oldZoomValue > [sender floatValue]) // then we are zooming in
{
    float zoomFactor = 1 + oldZoomValue - [sender floatValue];

    oldZoomValue = [sender floatValue];

    NSRect visible = [synchroS_ScrollView documentVisibleRect];
    NSRect newrect = NSInsetRect(visible, NSWidth(visible)*(1 - 1/zoomFactor)/2.0, NSHeight(visible)*(1 - 1/zoomFactor)/2.0);
    NSRect frame = [synchroS_ScrollView.documentView frame];

    [synchroS_ScrollView.documentView scaleUnitSquareToSize:NSMakeSize(zoomFactor, zoomFactor)];
    [synchroS_ScrollView.documentView setFrame:NSMakeRect(0, 0, frame.size.width * zoomFactor, frame.size.height * zoomFactor)];
    [[synchroS_ScrollView documentView] scrollPoint:newrect.origin];

    NSRect visibleI = [synchroI_ScrollView documentVisibleRect];
    NSRect newrectI = NSInsetRect(visibleI, NSWidth(visibleI)*(1 - 1/zoomFactor)/2.0, NSHeight(visibleI)*(1 - 1/zoomFactor)/2.0);
    NSRect frameI = [synchroI_ScrollView.documentView frame];

    [synchroI_ScrollView.documentView scaleUnitSquareToSize:NSMakeSize(zoomFactor, zoomFactor)];
    [synchroI_ScrollView.documentView setFrame:NSMakeRect(0, 0, frameI.size.width * zoomFactor, frameI.size.height * zoomFactor)];

    [[synchroI_ScrollView documentView] scrollPoint:newrectI.origin];
}
else
{
// the equivalent but for zoom-out
}

If I use the zoom functionality without synchronized Scroll's, both images on the NSScrollView are zoomed开发者_开发问答 nicely as expected. However, if they are synchronized, the program crashes with it seems to be a stack of several calls: on the main thread, it shows a lot of things like

#18 0x0000000100003e37 in -[SynchroScrollView synchronizedViewContentBoundsDidChange:] ()

and on the GDB:

This GDB was configured as "x86_64-apple-darwin".tty /dev/ttys000
sharedlibrary apply-load-rules all
[Switching to process 33162 thread 0x0]
[Switching to process 33162 thread 0xac03]
[Switching to process 33162 thread 0x903]
warning: Unable to restore previously selected frame.
warning: Unable to restore previously selected frame.
...
(gdb)

Can anyone point me a direction for debug or have any idea what is happening? Thank you for your help.

I'm not sure where you call the code for zooming the scrollView, but maybe zooming in scrollView A triggers zooming in scrollView B, which in turn triggers zooming in scrollView A again, creating an endless loop. changing the bounds in the synchronizedViewContentBoundsDidChange method would call the same method again and again.

I know this question is a few months old, but maybe this helps :)