Custom NSView background color not changing when switching in and out of dark mode - objective-c

Question

I cannot figure out how to update the background color of my custom NSView when the user switches in and out of dark mode.
I've read the documentation and followed instructions here:detecting darkmode
The strange thing is that I can get all the subviews to behave correctly, but for some strange reason I can't get the background color of the main view to change. The background color of the view looks correct when I start the app in either mode, but when I switch between modes while the app is running it doesn't update to the new theme.
Would be grateful for any suggestions.
Inside the Custom NSView I have the method
- (void) viewDidChangeEffectiveAppearance
{
self.needsDisplay = YES;
}
and inside the drawRect I have a do a simple color change before continuing with drawing in the view
NSAppearance *currentAppearance = [NSAppearance currentAppearance];
if (#available(*, macOS 10.14)) {
if(currentAppearance.name == NSAppearanceNameDarkAqua) {
red = 0.5*red+0.5;
green = 0.5*green+0.5;
blue = 0.5*blue+0.5;
}
}
Here is a screenshot of darkmode before (the way it should look)
Dark Mode Before
Here is a screenshot of light mode after user switch
Light Mode After
Here is a screenshot of lightmode before (the way it should look)
Light Mode Before
And here is a screenshot of darkmode after user switch
Dark Mode After
ps The reason I'm baffled and have little code to post is that the correct behavior is supposed to happen automatically with little effort. I even deleted the view from the nib and rebuilt it thinking maybe some setting got corrupted, but that didn't solve the problem.
Update: I found the source of the problem. This method gets called in windowDidLoad
- (void) setTransparent:(BOOL)transparent
{
if(transparent) {
[self.window setOpaque:NO];
NSColor *backgroundColor = [NSColor windowBackgroundColor];
backgroundColor = [backgroundColor colorWithAlphaComponent: .75];
[self.window setBackgroundColor:backgroundColor];
self.window.alphaValue = 0.75;
}
else {
[self.window setOpaque:YES];
NSColor *backgroundColor = [NSColor windowBackgroundColor];
backgroundColor = [backgroundColor colorWithAlphaComponent: 1];
[self.window setBackgroundColor:backgroundColor];
self.window.alphaValue = 1;
}
}
I get the expected behavior if I comment out the call to this method.
Why did this cause me to lose the automatic behavior of background color change when the user changes between light and dark mode?

Answer 1

My guess is that you’re not actually using the standard color for the background color.
You are using [NSColor windowBackgroundColor], however then making a copy with a different alpha component (via colorWithAlphaComponent), making it no longer a standard color.
My guess is a lot of the automatic ‘just works’ behaviour happens when you use the standard color definitions. As a test, could you try removing the colorWithAlphaComponent calls (where you are adding the transparency) from your settransparent method and see whether it works? if it does, you might need to find another way to add transparency to your view if you want the automatic behaviour.