What causes a white border to be applied to an NSProgressIndicator displayed in the system menu?

Question

This is what happens when I create an NSProgressIndicator and use NSStatusItem's -setView: method to display it in the menubar area while I'm performing an action:

What causes this border to be displayed, and how can I remove it? The intended result is that the control be transparent.

Here's the code I'm using:

NSProgressIndicator *progressIndicator = [[NSProgressIndicator alloc] init];

[progressIndicator setBezeled: NO];
[progressIndicator setStyle: NSProgressIndicatorSpinningStyle];
[progressIndicator setControlSize: NSSmallControlSize];
[progressIndicator sizeToFit];
[progressIndicator startAnimation: self];
[statusItem setView: progressIndicator]; // statusItem is an NSStatusItem instance
...
[statusItem setView: nil];
[progressIndicator stopAnimation: self];
[progressIndicator release];

Answer 1

Don’t scale the NSProgressIndicator though it’s also an NSView. Create a new view that resizes fine, position the status indicator in that view, and pass the enclosing view to -[NSStatusItem setView:]. Here is my implementation.

In NSStatusItem+AnimatedProgressIndicator.m,

- (void) startAnimation {

    NSView *progressIndicatorHolder = [[NSView alloc] init];

    NSProgressIndicator *progressIndicator = [[NSProgressIndicator alloc] init];

    [progressIndicator setBezeled: NO];
    [progressIndicator setStyle: NSProgressIndicatorSpinningStyle];
    [progressIndicator setControlSize: NSSmallControlSize];
    [progressIndicator sizeToFit];
    [progressIndicator setUsesThreadedAnimation:YES];

    [progressIndicatorHolder addSubview:progressIndicator];
    [progressIndicator startAnimation:self];

    [self setView:progressIndicatorHolder];

    [progressIndicator center];

    [progressIndicator setNextResponder:progressIndicatorHolder];
    [progressIndicatorHolder setNextResponder:self];

}

- (void) stopAnimation {

    [self setView:nil];

}

- (void) mouseDown:(NSEvent *) theEvent {

    [self popUpStatusItemMenu:[self menu]];

}

- (void) rightMouseUp:(NSEvent *) theEvent {}
- (void) mouseUp:(NSEvent *) theEvent {}
…

I added a custom method, -[NSView center], which does the following:

@implementation NSView (Centering)

- (void) center {

    if (![self superview]) return;

    [self setFrame:NSMakeRect(

        0.5 * ([self superview].frame.size.width - self.frame.size.width),
        0.5 * ([self superview].frame.size.height - self.frame.size.height), 

        self.frame.size.width, 
        self.frame.size.height

    )];

}

@end