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CoderGuy
Asked: 2022-11-02T07:51:12+00:00

Is there a way to use string interpolation with an SF Symbol that has a modifier on it?

I want to use string interpolation on an SF Symbol that has a rotationEffect(_:anchor:) modifier applied to it. Is it possible to do this?

Without the modifier this type of string interpolation works fine (in Swift 5.0):

struct ContentView: View {
    var body: some View {
        Text("Some text before \(Image(systemName: "waveform.circle")) plus some text after.")
    }
}

But applying the modifier like this:

struct ContentView: View {
    var body: some View {
        Text("Some text before \(Image(systemName: "waveform.circle").rotationEffect(.radians(.pi * 0.5))) plus some text after.")
    }
}

doesn’t compile and gives this error:

Instance method ‘appendInterpolation’ requires that ‘some View’ conform to ‘_FormatSpecifiable’

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1 Answer

  1. The Text interpolation expect an Image. When the .rotationEffect... is applied it becomes a View, and this is not valid.

    So an alternative is to rotate the SF before it is used in Image. This is what I ended up trying, using the code from one of the answers at: Rotating UIImage in Swift to rotate a UIImage and using that in the Image.

    It is a bit convoluted, and you will probably have to adjust the anchor/position. Perhaps someone will come up with a better solution. Until then it seems to works for me.

    struct ContentView: View {
    var body: some View {
        Text("Some text before \(img) plus some text after.")
    }
    
    var img: Image {
        if let uimg = UIImage(systemName: "waveform.circle"),
           let rotImage = uimg.rotate(radians: .pi/4) {
            return Image(uiImage: rotImage)
        } else {
            return Image(systemName: "waveform.circle")
        }
    }
     
}

// from: https://stackoverflow.com/questions/27092354/rotating-uiimage-in-swift
extension UIImage {
    func rotate(radians: Float) -> UIImage? {
        var newSize = CGRect(origin: CGPoint.zero, size: self.size).applying(CGAffineTransform(rotationAngle: CGFloat(radians))).size
        // Trim off the extremely small float value to prevent core graphics from rounding it up
        newSize.width = floor(newSize.width)
        newSize.height = floor(newSize.height)

        UIGraphicsBeginImageContextWithOptions(newSize, false, self.scale)
        let context = UIGraphicsGetCurrentContext()!

        // Move origin to middle
        context.translateBy(x: newSize.width/2, y: newSize.height/2)
        // Rotate around middle
        context.rotate(by: CGFloat(radians))
        // Draw the image at its center
        self.draw(in: CGRect(x: -self.size.width/2, y: -self.size.height/2, width: self.size.width, height: self.size.height))

        let newImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return newImage
    }
}
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