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Only measure selected bonsplit tab frame #22

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Only measure selected bonsplit tab frame #22

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18 changes: 9 additions & 9 deletions Sources/Bonsplit/Internal/Views/TabBarView.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -259,16 +259,16 @@ struct TabBarView: View {
controller.requestTabContextAction(action, for: TabID(id: tab.id), inPane: pane.id)
}
)
.background(
GeometryReader { geometry in
Color.clear.preference(
key: SelectedTabFramePreferenceKey.self,
value: pane.selectedTabId == tab.id
? geometry.frame(in: .named("tabBar"))
: nil
)
.background {
if pane.selectedTabId == tab.id {
GeometryReader { geometry in
Color.clear.preference(
key: SelectedTabFramePreferenceKey.self,
value: geometry.frame(in: .named("tabBar"))
)
}
}
)
}
Comment on lines +262 to +271
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@greptile-apps greptile-apps bot Mar 11, 2026

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Potential one-frame separator flicker on tab switch

With the old approach every tab always had a live GeometryReader in its background, so when selection moved from tab A to tab B the new GeometryReader (for B) was already laid out and could publish frame_B in the same render pass that tab A's GeometryReader went silent. With the new approach the GeometryReader for tab B is inserted for the first time on that render pass. SwiftUI needs to lay it out before it can publish a frame, which may introduce a single-frame window where no view publishes a preference value and SelectedTabFramePreferenceKey temporarily resolves to its defaultValue of nil. During that frame, tabBarBackground would render the separator as full-width (no gap) before the correct gap is restored on the next layout pass.

In practice this flicker (≤16 ms at 60 fps) is likely imperceptible during normal tab switching, but it is a subtle behavioral difference worth being aware of. If it ever becomes noticeable, one mitigation is to keep the previous frame cached in tabBarBackground until the preference produces a non-nil value:

.onPreferenceChange(SelectedTabFramePreferenceKey.self) { frame in
    if let frame {
        selectedTabFrameInBar = frame
    }
    // Intentionally skip nil to avoid a one-frame gap during tab transitions.
}

This keeps selectedTabFrameInBar at the last-known good frame during the brief transition window.

.onDrag {
createItemProvider(for: tab)
} preview: {
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