App Tyrant

Unlike UIScrollView on iOS, NSScrollView on Mac does not have a handy scrollEnabled property you can use to temporarily disable scrolling.

If you Google around, you can find several posts on websites like stackoverflow that ask questions like How can I disable the vertical scrolling of a NSScrollView? Some have suggested setting the hasVerticalScroller property to NO as the answer. However, the hasVerticalScroller property only effects the visibility of the scroller, a value of NO does not actually prevent scrolling.

There are also ways to constrain scrolling from an NSView subclass, as described in Apple’s documentation here. Constraining scrolling from a view subclass can be useful, but what if you want to just temporarily disable scrolling?

The easiest way to disable scrolling is to subclass NSScrollView and add a BOOL property with a name like scrollingEnabled. Then you can simply override the designated initializers (initWithFrame: and initWithCoder:) and set the ivar of the property to YES as the default value:

-(instancetype)initWithFrame:(NSRect)frameRect 
{ 
   self = [super initWithFrame:frameRect]; 
   if (self) 
   { 
       [self setUpOnInit]; 
   } 
   return self; 
}
 
- (instancetype)initWithCoder:(NSCoder *)coder 
{ 
    self = [super initWithCoder:coder]; 
    if (self) 
    { 
         [self setUpOnInit]; 
    } 
    return self; 
}
 
-(void)setUpOnInit
{
   // Set all default values. 
   _scrollingEnabled = YES; 
}

Now you can override the scrollWheel: method and check the property:

-(void)scrollWheel:(NSEvent *)theEvent 
{ 
    if (self.scrollingEnabled) {  
      [super scrollWheel:theEvent];  
     } 
    else {  
       // scrolling is disabled. 
    } 
}

This technique will work in most cases, but it isn’t enough to completely disable scrolling. If there is a view inside of a scroll view that implements autoscrolling behavior (if the view is a dragging destination) the scrollWheel: override won’t block scrolling during an attempted drag and drop operation. To disable scrolling in all cases, you should also subclass NSClipView and block scrolling by overriding the -constrainBoundsRect: method like this:

-(NSRect)constrainBoundsRect:(NSRect)proposedBounds
{
    MyScrollViewSubclass *mainScrollView = (MyScrollViewSubclass*)self.superview;
 
    if (mainScrollView.scrollingEnabled)
    {
        return [super constrainBoundsRect:proposedBounds];
    }
    else
    {
        // Disabled
        return self.documentVisibleRect;
    }
}

After you do that, scrolling should be disabled whenever you set the scrollingEnabled property to NO. But there may be cases where the scroll bar remains visible even when you have scrolling disabled (depending on what type of mouse is being used). To deal with this you should also make sure you set the hasVerticalScroller property to NO when you disable scrolling. If desired, you can implement the setter of the scrollingEnabled property and set hasVerticalScroller at the same time.