如何从 SwiftUI 中的 Color 获取 RGB 组件

Question

If I have a SwiftUI Color :

let col: Color = Color(red: 0.5, green: 0.5, blue: 0.5)

How do I get the RGB components from col ?
Like this maybe:

print(col.components.red)

In UIKit, I could use UIColor.getRed but there doesn't seem to be an equivalent in SwiftUI.

Answer 1

iOS 14 / macOS 10.16

There is a new initializer that takes a Color and returns a UIColor for iOS or NSColor for macOS now. With the help of those you can implement the following extensions:

iOS / macOS

import SwiftUI

#if canImport(UIKit)
import UIKit
#elseif canImport(AppKit)
import AppKit
#endif

extension Color {
    var components: (red: CGFloat, green: CGFloat, blue: CGFloat, opacity: CGFloat) {

        #if canImport(UIKit)
        typealias NativeColor = UIColor
        #elseif canImport(AppKit)
        typealias NativeColor = NSColor
        #endif

        var r: CGFloat = 0
        var g: CGFloat = 0
        var b: CGFloat = 0
        var o: CGFloat = 0

        guard NativeColor(self).getRed(&r, green: &g, blue: &b, alpha: &o) else {
            // You can handle the failure here as you want
            return (0, 0, 0, 0)
        }

        return (r, g, b, o)
    }
}

---

Usage

Color.red.components.red // 0.9999999403953552 // <- SwiftUI Colors are not pure!

Answer 2

Waiting for an API I've abused CustomStringConvertible protocol for the simple rgba case where the color description format is #rrggbbaa

debugPrint(Color.red)
debugPrint(Color(red: 1.0, green: 0.0, blue: 0.0))
debugPrint(Color(red: 1.0, green: 0.3, blue: 0.0))
debugPrint(Color(.sRGB, red: 1.0, green: 0.0, blue: 0.5, opacity: 0.3))
debugPrint(Color(hue: 1.0, saturation: 0.0, brightness: 1.0))
debugPrint(Color(.displayP3, red: 1.0, green: 0.0, blue: 0.0, opacity: 1.0).description)

red
#FF0000FF
#FF4C00FF
#FF00804D
#FFFFFFFF
"DisplayP3(red: 1.0, green: 0.0, blue: 0.0, opacity: 1.0)"

as you can see, things like Color.red just dump "red" but if you are working with simple RGB colors generated by code (ie from a color picker) then this is not too bad

extension SwiftUI.Color {
    var redComponent: Double? {
        let val = description
        guard val.hasPrefix("#") else { return nil }
        let r1 = val.index(val.startIndex, offsetBy: 1)
        let r2 = val.index(val.startIndex, offsetBy: 2)
        return Double(Int(val[r1...r2], radix: 16)!) / 255.0
    }

    var greenComponent: Double? {
        let val = description
        guard val.hasPrefix("#") else { return nil }
        let g1 = val.index(val.startIndex, offsetBy: 3)
        let g2 = val.index(val.startIndex, offsetBy: 4)
        return Double(Int(val[g1...g2], radix: 16)!) / 255.0
    }

    var blueComponent: Double? {
        let val = description
        guard val.hasPrefix("#") else { return nil }
        let b1 = val.index(val.startIndex, offsetBy: 5)
        let b2 = val.index(val.startIndex, offsetBy: 6)
        return Double(Int(val[b1...b2], radix: 16)!) / 255.0
    }

    var opacityComponent: Double? {
        let val = description
        guard val.hasPrefix("#") else { return nil }
        let b1 = val.index(val.startIndex, offsetBy: 7)
        let b2 = val.index(val.startIndex, offsetBy: 8)
        return Double(Int(val[b1...b2], radix: 16)!) / 255.0
    }
}

Answer 3

You can use UIColor and transform the UIColor to Color after. Code:

extension UIColor {
    func hexValue() -> String {
        let values = self.cgColor.components
        var outputR: Int = 0
        var outputG: Int = 0
        var outputB: Int = 0
        var outputA: Int = 1

        switch values!.count {
            case 1:
                outputR = Int(values![0] * 255)
                outputG = Int(values![0] * 255)
                outputB = Int(values![0] * 255)
                outputA = 1
            case 2:
                outputR = Int(values![0] * 255)
                outputG = Int(values![0] * 255)
                outputB = Int(values![0] * 255)
                outputA = Int(values![1] * 255)
            case 3:
                outputR = Int(values![0] * 255)
                outputG = Int(values![1] * 255)
                outputB = Int(values![2] * 255)
                outputA = 1
            case 4:
                outputR = Int(values![0] * 255)
                outputG = Int(values![1] * 255)
                outputB = Int(values![2] * 255)
                outputA = Int(values![3] * 255)
            default:
                break
        }
        return "#" + String(format:"%02X", outputR) + String(format:"%02X", outputG) + String(format:"%02X", outputB) + String(format:"%02X", outputA)
    }
}

Answer 4

The answer is no - there's no API do so (yet), but...

Most of SwiftUI structs have fields that are private , like in Color .

You can use Mirror to extract such informations - but keep in mind it is not efficient.

Here's how to extract the hexadecimal representation of a SwiftUI Color - for educational purpose.

Copy and paste this into a Xcode 11 playground.

import UIKit
import SwiftUI

let systemColor = Color.red
let color = Color(red: 0.3, green: 0.5, blue: 1)

extension Color {

    var hexRepresentation: String? {
        let children = Mirror(reflecting: color).children
        let _provider = children.filter { $0.label == "provider" }.first
        guard let provider = _provider?.value else {
            return nil
        }
        let providerChildren = Mirror(reflecting: provider).children
        let _base = providerChildren.filter { $0.label == "base" }.first
        guard let base = _base?.value else {
            return nil
        }
        var baseValue: String = ""
        dump(base, to: &baseValue)
        guard let firstLine = baseValue.split(separator: "\n").first,
              let hexString = firstLine.split(separator: " ")[1] as Substring? else {
            return nil
        }
        return hexString.trimmingCharacters(in: .newlines)
    }

}

systemColor.hexRepresentation
color.hexRepresentation

Colors like .red , .white , etc., don't seem to have many information in them, when dumped .

Just their "system" name.

▿ red
  ▿ provider: SwiftUI.(unknown context at $1297483bc).ColorBox<SwiftUI.SystemColorType> #0
    - super: SwiftUI.(unknown context at $129748300).AnyColorBox
    - base: SwiftUI.SystemColorType.red

A Color instantiated with red / blue / green components does instead.

▿ #4C80FFFF
  ▿ provider: SwiftUI.(unknown context at $11cd2e3bc).ColorBox<SwiftUI.Color._Resolved> #0
    - super: SwiftUI.(unknown context at $11cd2e300).AnyColorBox
    ▿ base: #4C80FFFF
      - linearRed: 0.073238954
      - linearGreen: 0.21404114
      - linearBlue: 1.0
      - opacity: 1.0

In the Playground, you will see:

• systemColor.hexRepresentation returning nil
• color.hexRepresentation returning "#4C80FFFF"

Answer 5

Based on @Mojtaba's answer, I came up with a shorter, more flexible version:

#if canImport(UIKit)
import UIKit
#elseif canImport(AppKit)
import AppKit
#endif

extension Color {
    #if canImport(UIKit)
    var asNative: UIColor { UIColor(self) }
    #elseif canImport(AppKit)
    var asNative: NSColor { NSColor(self) }
    #endif

    var rgba: (red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat) {
        let color = asNative.usingColorSpace(.deviceRGB)!
        var t = (CGFloat(), CGFloat(), CGFloat(), CGFloat())
        color.getRed(&t.0, green: &t.1, blue: &t.2, alpha: &t.3)
        return t
    }

    var hsva: (hue: CGFloat, saturation: CGFloat, value: CGFloat, alpha: CGFloat) {
        let color = asNative.usingColorSpace(.deviceRGB)!
        var t = (CGFloat(), CGFloat(), CGFloat(), CGFloat())
        color.getHue(&t.0, saturation: &t.1, brightness: &t.2, alpha: &t.3)
        return t
    }
}

Doing asNative.redComponent etc. might also work, FYI.

Answer 6

Simple one-liner:

print(UIColor(Color.blue).cgColor.components)

You get an [CGFloat]? of [red, green, blue, alpha].

Answer 7

I have found that @Mojtaba Hosseinis answer is working fine, except when you have your colors declared inside assets with light and dark appearances.

Then I found that the dark appearance somehow gets lost when using UIColor(self) . Here is a workaround I came up with:

Note, this is only for iOS since my app is iOS only, you could of course do the same as @Mojtaba Hosseini and adapt it to macOS as well.

extension Color {

    var components: (r: Double, g: Double, b: Double, o: Double)? {
        let uiColor: UIColor
        
        var r: CGFloat = 0
        var g: CGFloat = 0
        var b: CGFloat = 0
        var o: CGFloat = 0
        
        if self.description.contains("NamedColor") {
            let lowerBound = self.description.range(of: "name: \"")!.upperBound
            let upperBound = self.description.range(of: "\", bundle")!.lowerBound
            let assetsName = String(self.description[lowerBound..<upperBound])
            
            uiColor = UIColor(named: assetsName)!
        } else {
            uiColor = UIColor(self)
        }

        guard uiColor.getRed(&r, green: &g, blue: &b, alpha: &o) else { return nil }
        
        return (Double(r), Double(g), Double(b), Double(o))
    }
}

The idea is to use the UIColor(named:) initializer instead, where all appearances are correct. Fortunately, the name we set in assets is saved in the description of the Color . We only have to abstract it since there is also other information, namely bundle, etc.