Using the Klarna Express Button is easy to achieve and will provide a great user experience, just have to follow a few simple steps:

• Create the new Klarna Express Button with the parameters
• Setup event listener methods
• Add the view to the view hierarchy
• Setup the constraints
• Wait for user interaction

In order to initialize the express button the public API exposes the following initialization method which requires 4 parameters that can be later updated via setter methods:

self.button = KlarnaExpressButton(clientId: <YOUR-CLIENTID>, locale: String, returnURL: URL, eventHandler: KlarnaEventHandler)

To set up additional parameters that might be needed, the KlarnaComponent protocol which the express button implements, exposes a list of variables that can be used to update the values needed.

For example, to switch between environments while developing or releasing the app:

self.button.environment = .staging

The express button emits events to a handler every time something happens in the process, from initialization to completion. So it is important to pass a handler during init that conforms to the KlarnaEventHandler protocol.

This protocol exposes 2 useful methods, one for error cases and the other for everything else that is not considered an error:

// Events received
func klarnaComponent(_ klarnaComponent: KlarnaComponent, dispatchedEvent event: KlarnaProductEvent) {
 
}
 
// Errors received
func klarnaComponent(_ klarnaComponent: KlarnaComponent, encounteredError error: KlarnaError) {
 
}

self.button.translatesAutoresizingMaskIntoConstraints = false // When using autolayout
view.addSubView(self.button)
self.button.topAnchor.constraintEqual(to: view.topAnchor).isActive = true // or any other constraint method available

These are the predefined names for errors that can happen during the express button setup, or action:

// Errors received
func klarnaComponent(_ klarnaComponent: KlarnaComponent, encounteredError error: KlarnaError) {
      if error.name == KlarnaExpressButtonErrorName.KlarnaExpressButtonErrorInvalidParams {
         // The parameters set for Klarna Express Button are invalid
      }
      if error.name == KlarnaExpressButtonErrorName.KlarnaExpressButtonErrorRender {
         // Rendering the Klarna Express Button has failed
      }
}

The Express Button emits the following events upon user interaction (touch of the button):

// Events received
func klarnaComponent(_ klarnaComponent: KlarnaComponent, dispatchedEvent event: KlarnaProductEvent) {
      if event.action == .klarnaButtonUserTappedButton {
         // User tapped the Klarna Express Button
      }
      if event.action == .klarnaExpressButtonUserAuthenticated {
            // User is authenticated. You can read the user details      
            // in event.params attribute.
            let userDetails = event.params
      }

Depending on your preferences, you can customize the Express button to fit the look and feel of your cart page. Klarna offers several theme, label, and shape options to customize the Klarna Express Button's appearance to match the look and feel of your application.

This guideline will help you understand the different options available.

KlarnaButtonTheme

KlarnaButtonTheme enumeration will be used to define which style to be used, depending on either the app’s configuration or the system setting.

Name	Description	Express Button
Klarna	Renders the button in the Klarna pink theme. This is the recommended theme as it has the highest brand recognition and the likelihood of usage by your customers.
Light	Renders the button in white. It is recommended to use this theme on dark backgrounds.
Dark	Renders the button in black. It is recommended to use this theme on light backgrounds.
Auto	Automatic theme (light or dark) that will use the system’s user interface style.

KlarnaButtonShape

In order for the Klarna Express Button to fit into the aesthetic of your application, we offer different button shapes.

Name	Description	Express Button
RoundedRect	Renders the button as a rectangle with rounded corners.
Pill	Renders the button as a pill-shaped button.
Rectangle	Renders the button as a rectangle with square corners.

KlarnaButtonLabel

KlarnaButtonLabel enumeration will be used to select which label you wish to be shown on the button.

Name	Description	Express Button
KlarnaProduct	Renders the button with this product’s specific label which is “Klarna. Express Checkout”.
Klarna	Renders the button only with Klarna logo.