Screenlet Layer

The Screenlet layer contains the Screenlets available in Liferay Screens for Android. The following diagram uses Screenlet classes prefixed with MyScreenlet to show the Screenlet layer’s relationship with the core, View, and Interactor components.

Figure 1: This diagram illustrates the Android Screenlet layers relationship to other Screens components.

Figure 1: This diagram illustrates the Android Screenlet layer's relationship to other Screens components.

Screenlets are comprised of several Java classes and an XML descriptor file:

MyScreenletViewModel: an interface that defines the attributes shown in the UI. It typically accounts for all the input and output values presented to the user. For instance, LoginViewModel includes attributes like the user name and password. The Screenlet can read the attribute values, invoke Interactor operations, and change these values based on operation results.

MyScreenlet: a class that represents the Screenlet component the app developer interacts with. It includes the following things:

  • Attribute fields for configuring the Screenlet’s behavior. They are read in the Screenlet’s createScreenletView method and their default values can optionally be set there too.
  • A reference to the Screenlet’s View, specified by the liferay:layoutId attribute’s value. Note: a View must implement the Screenlet’s ViewModel interface.
  • Any number of methods for invoking Interactor operations. You can optionally make them public for app developers to call. They can also handle UI events received in the view class through a regular listener (such as Android’s OnClickListener) or events forwarded to the Screenlet via the performUserAction method.
  • An optional (but recommended) listener object for the Screenlet to call on a particular event.

MyScreenletInteractor: implements an end-to-end use case that communicates with a server or consumes a Liferay service. It might perform several intermediate steps. For example, it might send a request to a server, compute a local value based on the response, and then send this value to a different server. On completing an interaction, the Interactor must notify its listeners, one of which is typically the Screenlet class instance. The number of Interactors a Screenlet requires depends on the number of server use cases it supports. For example, the Login Screenlet class only supports one use case (log in the user), so it has only one Interactor. The DDL Forms Screenlet class, however, supports several use cases (load the form, load a record, submit the form, etc.), so it uses a different Interactor class for each use case.

MyScreenletConnector62 and MyScreenletConnector70: the classes that create the Interactors required to communicate with a specific Liferay version. The ServiceProvider creates a singleton ServiceVersionFactory that returns the right Connector.

MyScreenletDefaultView: a class that renders the Screenlet’s UI with the default layout. The class in Figure 3, for example, belongs to the Default View set. The View object and the layout file communicate using standard mechanisms, like a findViewById method or a listener object. User actions are received by a specified listener (for example, OnClickListener) and then passed to the Screenlet object via the performUserAction method.

myscreenlet_default.xml: an XML file that specifies how to render the Screenlet’s View. Here’s a skeleton of a Screenlet’s layout XML file:

<?xml version="1.0" encoding="utf-8"?>
<com.your.package.MyScreenletView 
    xmlns:android="http://schemas.android.com/apk/res/android">

    <!-- Put your regular components here: EditText, Button, etc. -->

</com.your.package.MyScreenletView>

Refer to the tutorial Creating Android Screenlets for more Screenlet details. Next, the View layer’s details are described.

High-Level Architecture

Core Layer

View Layer

Screenlet Lifecycle

« Core LayerView Layer »
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