SwiftUI navigationBarTitleでレイアウト警告

【SwiftUI】navigationBarTitleでレイアウトの警告が出る

2021.03.07

SwiftUI でナビゲーションバーを使った実装をしていると、実行時に LayoutConstraints の warning が表示されるようになっていました。

SwiftUISample[38246:1524076] [LayoutConstraints] Unable to simultaneously satisfy constraints.
	Probably at least one of the constraints in the following list is one you don't want. 
	Try this: 
		(1) look at each constraint and try to figure out which you don't expect; 
		(2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<NSLayoutConstraint:0x600001194aa0 'BIB_Trailing_CB_Leading' H:[_UIModernBarButton:0x7ffbc1d1b0b0]-(6)-[_UIModernBarButton:0x7ffbc1f18140'SwiftUI\U5b9f\U88c5\U30b5\U30f3\U30d7\U30eb']   (active)>",
    "<NSLayoutConstraint:0x600001194af0 'CB_Trailing_Trailing' _UIModernBarButton:0x7ffbc1f18140'SwiftUI\U5b9f\U88c5\U30b5\U30f3\U30d7\U30eb'.trailing <= _UIButtonBarButton:0x7ffbc1f178b0.trailing   (active)>",
    "<NSLayoutConstraint:0x6000011958b0 'UINav_static_button_horiz_position' _UIModernBarButton:0x7ffbc1d1b0b0.leading == UILayoutGuide:0x600000ba0e00'UIViewLayoutMarginsGuide'.leading   (active)>",
    "<NSLayoutConstraint:0x600001195900 'UINavItemContentGuide-leading' H:[_UIButtonBarButton:0x7ffbc1f178b0]-(0)-[UILayoutGuide:0x600000ba0d20'UINavigationBarItemContentLayoutGuide']   (active)>",
    "<NSLayoutConstraint:0x60000119cd70 'UINavItemContentGuide-trailing' UILayoutGuide:0x600000ba0d20'UINavigationBarItemContentLayoutGuide'.trailing == _UINavigationBarContentView:0x7ffbc1f10990.trailing   (active)>",
    "<NSLayoutConstraint:0x600001196080 'UIView-Encapsulated-Layout-Width' _UINavigationBarContentView:0x7ffbc1f10990.width == 0   (active)>",
    "<NSLayoutConstraint:0x60000119d130 'UIView-leftMargin-guide-constraint' H:|-(0)-[UILayoutGuide:0x600000ba0e00'UIViewLayoutMarginsGuide'](LTR)   (active, names: '|':_UINavigationBarContentView:0x7ffbc1f10990 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600001194aa0 'BIB_Trailing_CB_Leading' H:[_UIModernBarButton:0x7ffbc1d1b0b0]-(6)-[_UIModernBarButton:0x7ffbc1f18140'SwiftUI実装サンプル']   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKitCore/UIView.h> may also be helpful.

ソースコードとしてはこんな感じ。

struct ContentView: View {
    var body: some View {
        NavigationView {
            VStack {
                Text("Hello World!")
            }
            .navigationBarTitle("SwiftUI実装サンプル", displayMode: .inline)
        }
    }
}

調べてみるとこちらは現在非推奨になっているようでした。

navigationBarItems(leading:trailing:) | Apple Developer Documentation

Sets the navigation bar items for this view.

新たにできた実装方法だと toolbar を使うようですが、こちらは iOS14 以降で利用可能なため、iOS13 をサポートする場合は使うことができません。

追記：toolbar についても記事を書きました。

【SwiftUI】toolbarの使い方

とはいえ warning が出たままなのはなんとも気持ち悪いため調べたところ、どうやら .navigationViewStyle(StackNavigationViewStyle()) を追記すれば大丈夫なようでした。

SwiftUI NavigationView navigationBarTitle LayoutConstraints issue

This is maybe related to the new (12.3) version of XCode that came out recently but I have a very simple SwiftUI View: import SwiftUI struct HomeView: View { ...

struct ContentView: View {
    var body: some View {
        NavigationView {
            VStack {
                Text("Hello World!")
            }
            .navigationBarTitle("SwiftUI実装サンプル", displayMode: .inline)
        }
        .navigationViewStyle(StackNavigationViewStyle())
    }
}

これで warning が消えたので、とりあえずよしとします。