Is it possible to create a constants file on Swift?

Question

I have around 10 Swift 3 applications.

They are almost similar but there are some fields that changes in each application and I would like that these values could be used in the entirely program (for example: the name of each company, the primary colour on the application, etc). These values will be constant in the whole program.

I would like to create one constants file by application so the values that will be used on each application will be different from the others so I will not have to repeat on each program each value all the time. For example, if I set a constant named company and change its value to company1, company2, etc... depending on the file I can use that company constant in all the applications. So I will not have to replace the variable manually in the whole application each time I create a new one. Just replacing the corresponding values to each application.

So, is it possible to create a constants file? Maybe adding a special class. I guess that maybe it has another specific name but I could not find it.

Thanks in advance!

Answer 1

Yes you can create Constants file in Swift. Below are the ways.:

struct Constants {
    //App Constants
    static let APP_NAME = "YOUR_APP_NAME"
}

Usage:

print(Constants.APP_NAME)

Create a class and access via creating object:

class Constants{
     let APP_NAME = "YOUR APP NAME"
}

Usage:

let constInstance = Constants()
print(constInstance.APP_NAME)

The most efficient way is to go with struct.

Answer 2

It actually depends on what you want to define:

• In case of app's fonts, for example, declare an UIFont extension. In this way the precompiler can help you while writing code.

• In case of any particular constant (string, integers, etc..), I would create a Constants.swift file which contains only enums. The enum in this case is better than class or struct because it cannot be wrongly initialized

  enum Constants { static let appIdentifier: String = "string" }

It can only be used in this way: Constants.appIdentifier It cannot be initialized by doing Constants() (compiler will throw an error).

See https://www.natashatherobot.com/swift-enum-no-cases/ for more info

Answer 3

The cleanest way (following the file approach) is to use a Constants.swift file and structs that segment use cases for each variable set. For instance:

class Constants {

    struct Validation {
        static let InvalidValue = "n/a"
        static let IncompleteValue = "Incomplete"
    }

    struct Labels {
        static let Username = "Username"
    }

}

And to use simply:

print(Constants.Validation.InvalidValue)

This gives you more readable variables as well as organized and focused constants file. If the file gets too large you can then choose to split it into several files using the same approach.

Answer 4

Use Structure for define Constant.

Do As follow.

struct Company {
    static let kCountry1 = "Company1"
    static let kCountry2 = "Company2"
    static let kCountry3 = "Company3"
    static let kCountry4 = "Company4"
}

Use like this.

print(Company.kCountry1)

Answer 5

Constants are created with let in swift. Simply create a Constants.swift file and define your constants:

let mainColor = UIColor.green

You might want to version this separately and maybe add it to a custom framework.

Answer 6

Here is a slightly different solution not using a constants file, but a singleton class using a plist. This allows you to use one Settings file in all your applications, and then each application just needs a plist file.

If you add a plist to your project called "CustomSettings.plist" with the following contents:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>PrimaryColor</key>
    <string>cc3333</string>
    <key>CompanyName</key>
    <string>Company1</string>
</dict>
</plist>

Then create a new file called Settings with the following code:

public class Settings {
    static let instance = Settings()

    public let companyName: String
    public let primaryColor: UIColor

    private init() {
        let path = Bundle.main.path(forResource: "CustomSettings", ofType: "plist")!
        let settingsDict = NSDictionary(contentsOfFile: path) as! [String: AnyObject]

        companyName = settingsDict["CompanyName"] as! String
        let colorString = settingsDict["PrimaryColor"] as! String
        primaryColor = Settings.hexStringToUIColor(hex: colorString)
    }

    // Taken from: http://stackoverflow.com/questions/24263007/how-to-use-hex-colour-values-in-swift-ios
    private static func hexStringToUIColor (hex:String) -> UIColor {
        var cString:String = hex.trimmingCharacters(in: .whitespacesAndNewlines).uppercased()

        if (cString.hasPrefix("#")) {
            cString.remove(at: cString.startIndex)
        }

        if ((cString.characters.count) != 6) {
            return UIColor.gray
        }

        var rgbValue:UInt32 = 0
        Scanner(string: cString).scanHexInt32(&rgbValue)

        return UIColor(
            red: CGFloat((rgbValue & 0xFF0000) >> 16) / 255.0,
            green: CGFloat((rgbValue & 0x00FF00) >> 8) / 255.0,
            blue: CGFloat(rgbValue & 0x0000FF) / 255.0,
            alpha: CGFloat(1.0)
        )
    }
}

Now you only need one Settings file which you could have in a framework, and then each application only needs the CustomSettings plist file with the custom contents. You could use it as follows:

print (Settings.instance.companyName)
view.backgroundColor = Settings.instance.primaryColor