Selection Highlight in NSCollectionView

Its not too hard to do. Make sure "Selection" is enabled for the NSCollectionView in Interface Builder. Then in the NSView subclass that you are using for your prototype view, declare a property called "selected" :

@property (readwrite) BOOL selected;

UPDATED CODE HERE: (added super call)

Subclass NSCollectionViewItem and override -setSelected:

- (void)setSelected:(BOOL)flag
{
    [super setSelected:flag];
    [(PrototypeView*)[self view] setSelected:flag];
    [(PrototypeView*)[self view] setNeedsDisplay:YES];
}

Then you need to add code in your prototype view's drawRect: method to draw the highlight:

- (void)drawRect:(NSRect)dirtyRect 
{
    if (selected) {
       [[NSColor blueColor] set];
       NSRectFill([self bounds]);
    }
}

That just simply fills the view in blue when its selected, but that can be customized to draw the highlight any way you want. I've used this in my own apps and it works great.

If a different background color will suffice as a highlight, you could simply use an NSBox as the root item for you collection item view. Fill the NSBox with the highlight color of your choice. Set the NSBox to Custom so the fill will work. Set the NSBox to transparent.

Bind the transparency attribute of the NSBox to the selected attribute of File Owner(Collection Item) Set the value transformer for the transparent binding to NSNegateBoolean.

I tried to attach Interface builder screenshots but I was rejected bcos I'm a newbie :-(