Recommendation to avoid side jumping app issues

[eonist]

Full Recommendation: Preventing Popover Side-Jump in NSStatusItem Apps

Root Cause

NSPopover re-anchors its arrow horizontally whenever contentSize.width changes. If you pass a non-constant width — even once — the popover shifts left or right to re-centre its arrow on the status bar button. This is the side-jump.

The source of the non-constant width is NSHostingController.view.fittingSize.width. When any SwiftUI view in the tree uses .frame(maxHeight: .infinity), the layout engine returns an unstable width from fittingSize depending on which run-loop turn you sample it. You cannot reliably use it to drive contentSize.width.

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The Rule (Corrected)

Pin NSPopover.contentSize.width and setFrameSize width to a single constant. Let SwiftUI handle all child layout dynamically inside that fixed boundary.

AppKit sizing calls  →  always Self.fixedWidth  (one constant, never fittingSize.width)
SwiftUI layout       →  fully dynamic           (Spacer, maxWidth: .infinity, HStack, etc.)
fittingSize.height   →  safe to read dynamically (height doesn't shift the anchor)
fittingSize.width    →  never read back into any sizing call

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AppDelegate Rules

1. Declare one fixed-width constant

private static let fixedWidth: CGFloat = 480

This must match idealWidth in your root SwiftUI view. Change one, change both.

2. openPopover() — always use fixedWidth for width

private func openPopover() {
    let size = NSSize(
        width: Self.fixedWidth,                          // ← never fittingSize.width
        height: hostingController.view.fittingSize.height
    )
    hostingController.view.setFrameSize(size)
    popover.contentSize = size
    popover.show(relativeTo: button.bounds, of: button, preferredEdge: .maxY)
}

3. remeasurePopover() — same rule

private func remeasurePopover() {
    let newHeight = hostingController.view.fittingSize.height
    guard newHeight > 0 else { return }
    let newSize = NSSize(width: Self.fixedWidth, height: newHeight) // ← never fittingSize.width
    hostingController.view.setFrameSize(newSize)
    popover.contentSize = newSize
}

4. navigate() — resize asynchronously, never synchronously

private func navigate(to view: AnyView) {
    hostingController?.rootView = view
    guard popover?.isShown == true else { return }
    DispatchQueue.main.async { [weak self] in
        self?.remeasurePopover()
    }
}

5. For async-loaded content (e.g. log views) — use two async hops

onLogLoaded: {
    DispatchQueue.main.async {       // hop 1: SwiftUI commits new content
        DispatchQueue.main.async {   // hop 2: SwiftUI finishes layout
            self.remeasurePopover()  // now fittingSize.height is stable
        }
    }
}

One hop is not enough — fittingSize still reflects the spinner on the first turn after isLoading flips.

6. Never use sizingOptions = .preferredContentSize
This delegates width control to SwiftUI, which re-introduces the non-determinism you're trying to avoid.

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SwiftUI View Rules

Root view must use idealWidth, not fixed width

// ✅ Correct
.frame(idealWidth: 480, maxWidth: .infinity, alignment: .top)

// ❌ Wrong — prevents dynamic height measurement
.frame(width: 480)

idealWidth tells SwiftUI "lay out at 480pt" so fittingSize.height is measured at the right width. maxWidth: .infinity is required so the view fills the frame rather than collapsing.

All child views: fully dynamic — no restrictions

// ✅ All of this is fine inside the 480pt container
HStack {
    Text(title).layoutPriority(1)
    Spacer()
    Text(status).frame(width: 44) // fixed widths on leaf elements are fine too
}
.padding(.horizontal, 12)

Never add .frame(maxHeight:) to your root ScrollView
Height must be driven entirely by fittingSize.height in remeasurePopover(). Capping the ScrollView height here clips content and mis-sizes the popover.

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What Is and Isn't Hardcoded

Must be constant	Can be fully dynamic
NSPopover.contentSize.width	Every SwiftUI child view layout
setFrameSize width	HStack, Spacer, padding, Text
AppDelegate.fixedWidth	ScrollView content height
PopoverMainView .frame(idealWidth:)	fittingSize.height (used for vertical sizing)

The user never sees the fixedWidth constant — it just sets the canvas. Everything rendered inside it is fully responsive.