How to change NSPopover background color include triangle part?

Question

How can I change NSPopover background color include triangle part?

Answer 1

It's actually much simpler and you won't need private API.

Make the root view of your view controller a custom class

@implementation MyPopoverRootView

-(void)viewDidMoveToWindow
{
     NSView * aFrameView = [[self.window contentView] superview];
     MyPopoverBackgroundView * aBGView  =[[MyPopoverBackgroundView alloc] initWithFrame:aFrameView.bounds];
     aBGView.autoresizingMask = NSViewWidthSizable | NSViewHeightSizable;
     [aFrameView addSubview:aBGView positioned:NSWindowBelow relativeTo:aFrameView];
     [super viewDidMoveToWindow];
}

@end

Your background view just draws the desired color in its bounds.

@implementation MyPopoverBackgroundView

-(void)drawRect:(NSRect)dirtyRect
{
    [[NSColor whiteColor] set];
    NSRectFill(self.bounds);
}

@end