Toggling tabBarHidden destroys the tab's SwiftUI identity, dismissing presented sheets

[pawarren]

Before submitting a new issue

• I tested using the latest version of the library (1.4.0 is both latest and what we ship)
• I tested using a supported version of react native (0.86.3)
• I checked for possible duplicate issues

Bug summary

Toggling tabBarHidden at runtime tears down the tab's content and rebuilds it. A sheet presented from inside that tab is dismissed, and any @State in the subtree is lost.

We hit this on the common pattern of hiding the tab bar while the keyboard is up: a user typing in a sheet raises the keyboard, the app sets tabBarHidden, and their sheet disappears mid-edit.

Cause. hideTabBar is a @ViewBuilder whose branch depends on flag:

// ios/TabViewImpl.swift:537-553 @ 1.4.0
@ViewBuilder
func hideTabBar(_ flag: Bool) -> some View {
  #if !os(macOS)
    if flag {
      if #available(iOS 16.0, tvOS 16.0, *) {
        self.toolbar(.hidden, for: .tabBar)
      } else {
        // We fallback to isHidden on UITabBar
        self
      }
    } else {
      self
    }
  #else
    self
  #endif
}

A @ViewBuilder if/else compiles to _ConditionalContent<A, B>. Flipping flag swaps which branch is taken, which changes the view's type, which changes its structural identity. SwiftUI answers an identity change by discarding the subtree and building a new one — taking @State and any anchored presentation with it.

flag is a JS-driven prop, so this happens at runtime rather than once at setup:

ios/TabView/NewTabView.swift:45      .hideTabBar(props.tabBarHidden)
ios/TabView/LegacyTabView.swift:33   .hideTabBar(props.tabBarHidden)

Suggested fix

Take one branch, decided by availability — which is constant at runtime — and let only the toolbar value depend on flag:

@ViewBuilder
func hideTabBar(_ flag: Bool) -> some View {
  #if !os(macOS)
    if #available(iOS 16.0, tvOS 16.0, *) {
      // Keep the tab content's SwiftUI identity when tab-bar visibility changes.
      // Switching between a modified view and `self` tears down presentations
      // anchored in that tab.
      self.toolbar(flag ? .hidden : .automatic, for: .tabBar)
    } else {
      // We fallback to isHidden on UITabBar.
      self
    }
  #else
    self
  #endif
}

.automatic is the documented default for a toolbar's visibility, so the flag == false case keeps its current behaviour while the view keeps its identity. The pre-iOS-16 fallback is unchanged and still cannot hide the bar this way; that branch is now chosen by availability alone, so it no longer participates in identity changes either.

This is the diff we currently carry as a patch:

   @ViewBuilder
   func hideTabBar(_ flag: Bool) -> some View {
     #if !os(macOS)
-      if flag {
-        if #available(iOS 16.0, tvOS 16.0, *) {
-          self.toolbar(.hidden, for: .tabBar)
-        } else {
-          // We fallback to isHidden on UITabBar
-          self
-        }
+      if #available(iOS 16.0, tvOS 16.0, *) {
+        // Keep the tab content's SwiftUI identity when keyboard visibility
+        // changes. Switching between a modified view and `self` tears down
+        // presentations anchored in that tab, including Expo UI sheets.
+        self.toolbar(flag ? .hidden : .automatic, for: .tabBar)
       } else {
+        // We fallback to isHidden on UITabBar.
         self
       }
     #else

Happy to open a PR.

Library version

1.4.0

Environment info

react-native: 0.86.3
expo: 57.0.20
react: 19.2.3
react-native-bottom-tabs: 1.4.0
platform: iOS (real device and simulator)
architecture: Fabric (New Architecture)

Steps to reproduce

The reproduction is pure SwiftUI — no React Native and no dependency on this library, which is what shows the cause is the @ViewBuilder branch rather than anything about the bridge, the props, or the app.

1. Download IdentityRepro.swift from the gist below
2. Drop it into an iOS app target, or open it in an Xcode Preview
3. Increment both counters, and/or tap "present sheet" on either side
4. Flip the tabBarHidden toggle

Expected: both columns keep their state.
Actual: the UPSTREAM column resets its counter to 0 and dismisses its sheet; the FIXED column keeps both.

The file defines hideTabBar_upstream (verbatim from TabViewImpl.swift) and hideTabBar_fixed (the suggestion above) side by side over identical subtrees.

iOS/tvOS only — .toolbar(_:for: .tabBar) is unavailable on macOS, which is why the library's own function is wrapped in #if !os(macOS).

Reproducible sample code

https://gist.github.com/pawarren/56cbb014c18150e67995bf6f11ff8168