autohide only horizontal scroller in NSScrollView

Question

I have an NSTableView, created from IB, that I want to only autohide the horizontal scroller on. The main reason I want to do this is because it seems the NSTableView corverView only get's displayed if there is a vertical scroller.

I can't find any method to do this with the base class. So I tried subclassing NSScrollView and observing the hidden key on the horizontal scroller (code below). This works; however, the view tries to reset the current visible options every time the user resizes the window. This makes my implementation somewhat expensive; and it seems inelegant. Any better ideas about how to do this?

Thanks in advance!

Current implementation:

@interface PVScrollView : NSScrollView {
  BOOL autohidesHorizontalScroller;
}

@property(assign) BOOL autohidesHorizontalScroller;

- (void) viewResized:(NSNotification*)notification;

@end

@implementation PVScrollView

@synthesize autohidesHorizontalScroller;

- (void) setAutohidesHorizontalScroller:(BOOL)val
{
  autohidesHorizontalScroller = val;
  [self setAutohidesScrollers:NO];
  [[self horizontalScroller] addObserver:self 
                              forKeyPath:@"hidden"
                                 options:0 
                                 context:nil];

}

- (void) observeValueForKeyPath:(NSString *)keyPath 
                       ofObject:(id)object 
                         change:(NSDictionary *)change 
                        context:(void *)context
{
  if (!([self documentVisibleRect].size.width < [[self documentView] frame].size.width) )
  {
    // remove observer
    [[self horizontalScroller] removeObserver:self
                                   forKeyPath:@"hidden"];
    [[self horizontalScroller] setHidden:YES];
    //[[self horizontalScroller] setNeedsDisplay:YES];
    // add it back
    [[self horizontalScroller] addObserver:self 
                                forKeyPath:@"hidden"
                                   options:0 
                                   context:nil];
  }
}

@end

Answer 1

Give this a shot in your NSScrollView subclass:

- (void)setFrameSize:(NSSize)newSize;
{
    NSSize minFrameSize = [NSScrollView frameSizeForContentSize:[self contentSize] hasHorizontalScroller:NO hasVerticalScroller:YES borderType:[self borderType]];
    BOOL wantScroller = minFrameSize.width > newSize.width;
    [self setHasHorizontalScroller:wantScroller];        
    [super setFrameSize: newSize];
}

You'll need to check "Show Vertical Scroller" and uncheck "Automatically Hide Scrollers" for it to work; I didn't bother making it robust to changes in IB. Also, you'll need to do the same thing when the window is first displayed (in the NSScrollView constructor).

I compared CPU usage with and without this change; it seems to vary at most 1% (19%→20%) in my test application.