add convenience init to UIColor that takes a hex string as input parameter

deltachat-ios/Utils.swift

@@ -60,4 +60,23 @@ extension UIColor {
         
         self.init(alpha: alpha, red:(netHex >> 16) & 0xff, green:(netHex >> 8) & 0xff, blue:netHex & 0xff)
     }
+
+    // see: https://stackoverflow.com/a/33397427
+    convenience init(hexString: String) {
+        let hex = hexString.trimmingCharacters(in: CharacterSet.alphanumerics.inverted)
+        var int = UInt32()
+        Scanner(string: hex).scanHexInt32(&int)
+        let a, r, g, b: UInt32
+        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) = (255, 0, 0, 0)
+        }
+        self.init(red: CGFloat(r) / 255, green: CGFloat(g) / 255, blue: CGFloat(b) / 255, alpha: CGFloat(a) / 255)
+    }
 }