Use Hex color in SwiftUI

Try this:

extension Color {
    init(hex: Int, opacity: Double = 1.0) {
        let red = Double((hex & 0xff0000) >> 16) / 255.0
        let green = Double((hex & 0xff00) >> 8) / 255.0
        let blue = Double((hex & 0xff) >> 0) / 255.0
        self.init(.sRGB, red: red, green: green, blue: blue, opacity: opacity)
    }
}

Usage:

Text("Hello World!")
    .background(Color(hex: 0xf5bc53))

Text("Hello World!")
    .background(Color(hex: 0xf5bc53, opacity: 0.8))

You're almost there, you were using the wrong initialiser parameter:

extension Color {
    init(hex: String) {
        let hex = hex.trimmingCharacters(in: CharacterSet.alphanumerics.inverted)
        var int: UInt64 = 0
        Scanner(string: hex).scanHexInt64(&int)
        let a, r, g, b: UInt64
        switch hex.count {
        case 3: // RGB (12-bit)
            (a, r, g, b) = (255, (int >> 8) * 17, (int >> 4 & 0xF) * 17, (int & 0xF) * 17)
        case 6: // RGB (24-bit)
            (a, r, g, b) = (255, int >> 16, int >> 8 & 0xFF, int & 0xFF)
        case 8: // ARGB (32-bit)
            (a, r, g, b) = (int >> 24, int >> 16 & 0xFF, int >> 8 & 0xFF, int & 0xFF)
        default:
            (a, r, g, b) = (1, 1, 1, 0)
        }

        self.init(
            .sRGB,
            red: Double(r) / 255,
            green: Double(g) / 255,
            blue:  Double(b) / 255,
            opacity: Double(a) / 255
        )
    }
}

Here is a Playground with my solution. It adds fallbacks after fallbacks and only relies on the hexString for color and alpha.

import SwiftUI

extension Color {
    init(hex string: String) {
        var string: String = string.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines)
        if string.hasPrefix("#") {
            _ = string.removeFirst()
        }

        // Double the last value if incomplete hex
        if !string.count.isMultiple(of: 2), let last = string.last {
            string.append(last)
        }

        // Fix invalid values
        if string.count > 8 {
            string = String(string.prefix(8))
        }

        // Scanner creation
        let scanner = Scanner(string: string)

        var color: UInt64 = 0
        scanner.scanHexInt64(&color)

        if string.count == 2 {
            let mask = 0xFF

            let g = Int(color) & mask

            let gray = Double(g) / 255.0

            self.init(.sRGB, red: gray, green: gray, blue: gray, opacity: 1)

        } else if string.count == 4 {
            let mask = 0x00FF

            let g = Int(color >> 8) & mask
            let a = Int(color) & mask

            let gray = Double(g) / 255.0
            let alpha = Double(a) / 255.0

            self.init(.sRGB, red: gray, green: gray, blue: gray, opacity: alpha)

        } else if string.count == 6 {
            let mask = 0x0000FF
            let r = Int(color >> 16) & mask
            let g = Int(color >> 8) & mask
            let b = Int(color) & mask

            let red = Double(r) / 255.0
            let green = Double(g) / 255.0
            let blue = Double(b) / 255.0

            self.init(.sRGB, red: red, green: green, blue: blue, opacity: 1)

        } else if string.count == 8 {
            let mask = 0x000000FF
            let r = Int(color >> 24) & mask
            let g = Int(color >> 16) & mask
            let b = Int(color >> 8) & mask
            let a = Int(color) & mask

            let red = Double(r) / 255.0
            let green = Double(g) / 255.0
            let blue = Double(b) / 255.0
            let alpha = Double(a) / 255.0

            self.init(.sRGB, red: red, green: green, blue: blue, opacity: alpha)

        } else {
            self.init(.sRGB, red: 1, green: 1, blue: 1, opacity: 1)
        }
    }
}

let gray0 = Color(hex: "3f")
let gray1 = Color(hex: "#69")
let gray2 = Color(hex: "#6911")
let gray3 = Color(hex: "fff")
let red = Color(hex: "#FF000044s")
let green = Color(hex: "#00FF00")
let blue0 = Color(hex: "0000FF")
let blue1 = Color(hex: "0000F")

For getting the hexString from Color.. well, this is not a public API. We still need to rely on UIColor implementations for that.

PS: I saw the components solution below.. but if the API changes in the future, my version is a bit more stable.

Another alternative below that uses Int for hex but of course, it can be changed to String if you prefer that.

extension Color {
    init(hex: UInt, alpha: Double = 1) {
        self.init(
            .sRGB,
            red: Double((hex >> 16) & 0xff) / 255,
            green: Double((hex >> 08) & 0xff) / 255,
            blue: Double((hex >> 00) & 0xff) / 255,
            opacity: alpha
        )
    }
}

Usage examples:

Color(hex: 0x000000)
Color(hex: 0x000000, alpha: 0.2)