How do I do something after the next NSView -layout has occurred?

Question

In response to a user event, I want to:

• add a new NSView to the window, and then
• show an NSPanel positioned just below that view

I have each half of this done. I can add a new subview, and the container view's -updateConstraints identifies it and adds the correct layout constraints, so that the next time layout is performed, it's positioned correctly in the window. Also, I have a NSWindowController subclass that puts the panel on the screen.

Unfortunately, there's an ordering problem. My panel's controller just looks at the new NSView's frame property for deciding where to put it, but during this iteration of the main event loop, the -layout method hasn't been called yet, so it's still positioned at (0,0).

(If I separate these two pieces of functionality, and require two separate user events for "add view" and "create panel", then the panel is correctly positioned below the view.)

Is there a way to attach an NSPanel to an NSView, as if with a layout constraint? Or is there a way to say "do this (window controller stuff), but only after the next -layout call"?

Answer 1

Just call -layoutSubtreeIfNeeded on your NSView’s superview as soon as you add it and its constraints, so it will lay out immediately, then add the panel.

Or use an NSPopOver, although those draw a certain way and you might not want that.