How to customize disclosure cell in view-based NSOutlineView

Question

I'm trying to customize the disclosure arrow appearance in my view-based NSOutlineView. I saw that it's recommended to use

- (void)outlineView:(NSOutlineView *)outlineView willDisplayOutlineCell:(id)cell forTableColumn:(NSTableColumn *)tableColumn item:(id)item

delegate method to achieve it. The problem is that this method is not called for some reason. I have 2 custom cell views - one for item and second for header item. May be this method is not called for view-based outline views? May be something became broken in Lion?

Please shed some light.

Answer 1

Solution 1:

Subclass NSOutlineView and override makeViewWithIdentifier:owner:

- (id)makeViewWithIdentifier:(NSString *)identifier owner:(id)owner {
    id view = [super makeViewWithIdentifier:identifier owner:owner];

    if ([identifier isEqualToString:NSOutlineViewDisclosureButtonKey]) {
        // Do your customization
    }

    return view;
}

For Source Lists use NSOutlineViewShowHideButtonKey.

Solution 2:

Interface Builder

The button is added to the column and the identifier set to NSOutlineViewDisclosureButtonKey.

Official documentation from NSOutlineView.h

/* The following NSOutlineView*Keys are used by the View Based NSOutlineView to create the "disclosure button" used to collapse and expand items. The NSOutlineView creates these buttons by calling [self makeViewWithIdentifier:owner:] passing in the key as the identifier and the delegate as the owner. Custom NSButtons (or subclasses thereof) can be provided for NSOutlineView to use in the following two ways:
 1. makeViewWithIdentifier:owner: can be overridden, and if the identifier is (for instance) NSOutlineViewDisclosureButtonKey, a custom NSButton can be configured and returned. Be sure to set the button.identifier to be NSOutlineViewDisclosureButtonKey.
 2. At design time, a button can be added to the outlineview which has this identifier, and it will be unarchived and used as needed.
 
 When a custom button is used, it is important to properly set up the target/action to do something (probably expand or collapse the rowForView: that the sender is located in). Or, one can call super to get the default button, and copy its target/action to get the normal default behavior.
 
 NOTE: These keys are backwards compatible to 10.7, however, the symbol is not exported prior to 10.9 and the regular string value must be used (i.e.: @"NSOutlineViewDisclosureButtonKey").
 */
APPKIT_EXTERN NSString *const NSOutlineViewDisclosureButtonKey NS_AVAILABLE_MAC(10_9); // The normal triangle disclosure button
APPKIT_EXTERN NSString *const NSOutlineViewShowHideButtonKey NS_AVAILABLE_MAC(10_9); // The show/hide button used in "Source Lists"

Answer 2

This answer is written with OS X 10.7 in mind, for newer versions of OS X/macOS, refer to WetFish's answer

That method does not get called because it is only relevant for cell based outline views.

In a view based outline view, the disclosure triangle is a regular button in the row view of expandable rows. I don't know where it gets added, but it does, and NSView's didAddSubview: method handles exactly that situation of a view being added somewhere else.

Hence, subclass NSTableRowView, and override didAddSubview:, like this:

-(void)didAddSubview:(NSView *)subview
{
    // As noted in the comments, don't forget to call super:
    [super didAddSubview:subview];

    if ( [subview isKindOfClass:[NSButton class]] ) {
        // This is (presumably) the button holding the 
        // outline triangle button.
        // We set our own images here.
        [(NSButton *)subview setImage:[NSImage imageNamed:@"disclosure-closed"]];
        [(NSButton *)subview setAlternateImage:[NSImage imageNamed:@"disclosure-open"]];
    }
}

Of course, your outline view's delegate will have to implement outlineView:rowViewForItem: to return the new row view.

Despite the name, frameOfOutlineCellAtRow: of NSOutlineView still gets called for view based outline views, so for the positioning of your triangle, you might want to subclass the outline view and override that method, too.

Answer 3

For Swift 4.2 macOS 10.14, @WetFish's answer can be implemented as follows:

class SidebarView: NSOutlineView {

  override func makeView(withIdentifier identifier: NSUserInterfaceItemIdentifier, owner: Any?) -> NSView? {
    let view = super.makeView(withIdentifier: identifier, owner: owner)

    if identifier == NSOutlineView.disclosureButtonIdentifier {
      if let btnView = view as? NSButton {
        btnView.image = NSImage(named: "RightArrow")
        btnView.alternateImage = NSImage(named: "DownArrow")

        // can set properties of the image like the size
        btnView.image?.size = NSSize(width: 15.0, height: 15.0)
        btnView.alternateImage?.size = NSSize(width: 15.0, height: 15.0)
      }
    }
    return view
  }

}

Looks quite nice!