Using and Creating Progress Presenters

Many apps display a progress indicator while performing an operation. For example, you’ve likely seen the spinners in iOS apps that let you know the app is performing some kind of work. For more information, see the iOS Human Interface Guidelines article on Progress Indicators.

You can display these in Screenlets by using classes that conform the ProgressPresenter protocol. Liferay Screens includes two such classes:

This tutorial shows you how to use and create progress presenters, using code from the advanced version of the sample Add Bookmark Screenlet as an example. First, you’ll learn how to use progress presenters.

Using Progress Presenters

The BaseScreenletView class contains the default progress presenter functionality. To show a presenter other than the default MBProgressHUDPresenter, your View class must therefore override certain BaseScreenletView functionality. Follow these steps to do this:

  1. In your View class, override the BaseScreenletView method createProgressPresenter to return an instance of the desired presenter. For example, to use NetworkActivityIndicatorPresenter in the sample Add Bookmark Screenlet, you must override the createProgressPresenter method in AddBookmarkView_default to return a NetworkActivityIndicatorPresenter instance:

     override func createProgressPresenter() -> ProgressPresenter {
         return NetworkActivityIndicatorPresenter()
  2. In your View class, override the BaseScreenletView property progressMessages to return the messages you want to use in the presenter. If the presenter doesn’t display messages, then return an empty string. The progressMessages property should return the messages as [String : ProgressMessages], where String is the Screenlet’s action name. ProgressMessages is a type alias representing a dictionary where the progress type is the key, and the actual message is the value. The three possible progress types correspond to the Screenlet action’s status: Working, Failure, or Success. The progressMessages property therefore lets the presenter display the appropriate message for the Screenlet action’s current status.

    For example, the following code overrides the progressMessages property in Add Bookmark Screenlet’s View class (AddBookmarkView_default). For each Screenlet action (AddBookmarkAction and GetTitleAction), a message (NoProgressMessage) is assigned to the Screenlet operation’s Working status. Since NoProgressMessage is an alias for an empty string, this tells the presenter to display no message when the Screenlet attempts to add a bookmark or get a title. Note, however, that the presenter still displays its progress indicator:

     override var progressMessages: [String : ProgressMessages] {
         return [
             AddBookmarkScreenlet.AddBookmarkAction : [.Working: NoProgressMessage],
             AddBookmarkScreenlet.GetTitleAction : [.Working: NoProgressMessage],

    To display a message, replace NoProgressMessage with your message. For example, the following code defines separate messages for Working, Success, and Failure:

     override var progressMessages: [String : ProgressMessages] {
         return [
             AddBookmarkScreenlet.AddBookmarkAction : [
                 .Working: "Saving bookmark...",
                 .Success: "Bookmark saved!",
                 .Failure: "An error occurred saving the bookmark"
             AddBookmarkScreenlet.GetTitleAction : [
                 .Working: "Getting site title...",
                 .Failure: "An error occurred retrieving the title"

Great! Now you know how to use progress presenters. Next, you’ll learn how to create your own.

Creating Progress Presenters

Creating your own progress presenter isn’t as complicated as you might think. Recall that a presenter in Liferay Screens is a class that conforms the ProgressPresenter protocol. You can create your presenter by conforming this protocol from scratch, or by extending one of Screens’s existing presenters that already conform this protocol (MBProgressHUDPresenter or NetworkActivityIndicatorPresenter). In most cases, extending MBProgressHUDPresenter is sufficient.

For example, Add Bookmark Screenlet’s AddBookmarkProgressPresenter extends MBProgressHUDPresenter to display a different progress indicator for the Screenlet’s get title action. Use the following steps to create a progress presenter that extends from an existing presenter. As an example, these steps extend MBProgressHUDPresenter to add a progress indicator for the get title button:

  1. In your View’s XIB file, add the activity indicator you want to use. For example, the XIB file in Add Bookmark Screenlet contains an iOS UIActivityIndicatorView over the get title button:

    Figure 1: The updated Add Bookmark Screenlets XIB file contains a new activity indicator over the get title button.

    Figure 1: The updated Add Bookmark Screenlet's XIB file contains a new activity indicator over the get title button.

  2. In your View class, create an outlet for the XIB’s new activity indicator. For example, Add Bookmark Screenlet’s View class (AddBookmarkView_default) contains an @IBOutlet for the UIActivityIndicatorView from the XIB:

     @IBOutlet weak var activityIndicatorView: UIActivityIndicatorView?

Now you must create your presenter class. You’ll do this here by extending an existing presenter class. Use the following steps to do this:

  1. Extend the existing presenter class you want to base your presenter on. Your presenter class must contain properties for your presenter’s activity indicator and any other UI components. It must also contain an initializer that sets these properties. For example, AddBookmarkProgressPresenter extends MBProgressHUDPresenter and contains properties for the get title button and UIActivityIndicatorView. Its initializer sets these properties:

     public class AddBookmarkProgressPresenter: MBProgressHUDPresenter {
         let button: UIButton?
         let activityIndicator: UIActivityIndicatorView?
         public init(button: UIButton?, activityIndicator: UIActivityIndicatorView?) {
             self.button = button
             self.activityIndicator = activityIndicator
  2. Implement your presenter’s behavior by overriding the appropriate methods from the presenter class that you’re extending. For example, AddBookmarkProgressPresenter overrides MBProgressHUDPresenter’s showHUDInView and hideHUDFromView methods. The overridden showHUDInView method hides the button and starts animating the activity indicator. The overridden hideHUDFromView method stops this animation and restores the button:

     public override func showHUDInView(view: UIView, message: String?, 
         forInteractor interactor: Interactor) {
             guard interactor is GetWebTitleInteractor else {
                 return super.showHUDInView(view, message: message, 
                     forInteractor: interactor)
             button?.hidden = true
     public override func hideHUDFromView(view: UIView?, message: String?, 
         forInteractor interactor: Interactor, withError error: NSError?) {
             guard interactor is GetWebTitleInteractor else {
                 return super.hideHUDFromView(view, message: message, 
                     forInteractor: interactor, withError: error)
             button?.hidden = false

Great, that’s it! Now you can use your presenter the same way you would any other.

Creating iOS Screenlets

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Architecture of Liferay Screens for iOS

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