swift - How we can get and read size of a Text with GeometryReader in SwiftUI?

Question

I am trying to read the width of my Text depending on size of Text Font, As we know GeometryReader takes all possible given place to him, in this codes it just take himself the given frame size, that I passed it, but it does not take size of my Text! what I am doing Wrong? I what GeometryReader start reading my Text size only! not himself frame width.

Here is my code:

struct ContentView: View {
    @State var fontSize: CGFloat = 20.0

    var body: some View {
        Spacer()

        textWidthGeometryReader(fontSize: $fontSize)

        Spacer()

        Text("Font size:" + "(fontSize)")

        Slider(value: $fontSize, in: 20...40, step: 1)
            .padding()

        Spacer()
    }
}

struct textWidthGeometryReader: View {
    @Binding var fontSize: CGFloat

    var body: some View {
        GeometryReader { inSideGeometry in

            Text("width of Text:" + String(format: "%.0f", inSideGeometry.size.width))
                .font(.system(size: fontSize))
                .background(Color.yellow)
                .position(x: inSideGeometry.size.width / 2, y: inSideGeometry.size.height / 2)
        }
        .frame(width: 400, height: 300, alignment: .center)
        .background(Color.gray)
        .cornerRadius(20)
    }
}

Answer 1

You can use view preferences.

1. First create a custom PreferenceKey for the view size:

struct ViewSizeKey: PreferenceKey {
    static var defaultValue: CGSize = .zero

    static func reduce(value: inout CGSize, nextValue: () -> CGSize) {
        value = nextValue()
    }
}

2. Create a view which will calculate its size and assign it to the ViewSizeKey:

struct ViewGeometry: View {
    var body: some View {
        GeometryReader { geometry in
            Color.clear
                .preference(key: ViewSizeKey.self, value: geometry.size)
        }
    }
}

3. Use them in your view:

struct ContentView: View {
    @State var fontSize: CGFloat = 20.0
    @State var textSize: CGSize = .zero

    var body: some View {
        Spacer()
        Text("width of Text:" + String(format: "%.0f", textSize.width))
            .font(.system(size: fontSize))
            .background(ViewGeometry())
            .onPreferenceChange(ViewSizeKey.self) {
                textSize = $0
            }
        Spacer()
        Text("Font size:" + "(fontSize)")
        Slider(value: $fontSize, in: 20...40, step: 1)
            .padding()
        Spacer()
    }
}

---

View Preferences is quite an advanced topic. You can find a more detailed explanation here:

• The magic of view preferences in SwiftUI
• Inspecting the View Tree – Part 1: PreferenceKey