Using GeometryReader in a ViewModifier doesn't render the view

Question

I have a custom modifier to handle show/hide keyboard, but when running on iOS 13 it doesn't render the view, after some investigation I found that the cause is a usage of GeometryReader in a ViewModifier.

The following code will result in a blank screen:

struct ContentView: View {
    var body: some View {
        Text("Foo")
            .modifier(MyCustomModifier())
    }
}

struct MyCustomModifier: ViewModifier {
    func body(content: Content) -> some View {
        GeometryReader { proxy in
            content
            // Use proxy
        }
    }
}

It happens only for iOS 13 and only if the code is compiled with Xcode 12.

Oleg Sherman · Accepted Answer · 2020-10-15 13:03:19Z

3

It looks like a bug so as a workaround there are two thing that can be done:

1.Use the GeometryReader outside the modifier and pass the proxy to the modifier:

struct ContentView: View {
    var body: some View {
        GeometryReader { proxy in
            Text("Foo")
                .modifier(MyCustomModifier(geometryProxy: proxy))
        }
    }
}

struct MyCustomModifier: ViewModifier {
    let geometryProxy: GeometryProxy
    
    func body(content: Content) -> some View {
        content
        // Use proxy
    }
}

2.Just embed the view that uses the modifier in a GeometryReader:

struct ContentView: View {
    var body: some View {
        GeometryReader { _ in
            Text("Foo")
                .modifier(MyCustomModifier())
        }
    }
}

struct MyCustomModifier: ViewModifier {
    func body(content: Content) -> some View {
        GeometryReader { proxy in
            content
            // Use proxy
        }
    }
}

answered Oct 15, 2020 at 13:03

Oleg Sherman

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1 Comment

lazarevzubov Over a year ago

(1) didn't change anything in my case but (2) worked as a charm, thanks.

user11873221 · Accepted Answer · 2020-10-30 10:28:28Z

I had the same issue and had to forfeit using ViewModifier altogether and switch to the good old approach with view wrapping in an extension:

extension View {

    /// Conditionally applies bottom padding to the view, if there's no
    /// bottom safe area inset (or if it's less than the padding provided).
    /// - Parameter padding: The min bottom padding to apply.
    @available(iOS, deprecated: 14, message: "Time to switch to the ViewModifier approach.")
    func minBottomPadding(_ padding: CGFloat) -> some View {
        // Currently there's a bug that prevents using GeometryReader inside ViewModifier on iOS 13.
        GeometryReader { geometry in
            self.padding(.bottom, geometry.safeAreaInsets.bottom < padding ? padding : 0)
        }
    }
}

Thank you @oleg-sherman for confirming my suspicions!

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