Roku SDK Documentation : Downloading Server Content

Table of Contents

Various types of content material can be downloaded from your server to a SceneGraph application. Many of the renderable nodes include a uri field that allows you specify the URI of a graphical image file or other content on your server. Setting this field causes the node to automatically download the content to the SceneGraph node, and for graphical images, be rendered on the display screen according the configuration of the node.

For many nodes that require more complex data, a content field is provided. This special field is designed to be assigned the value of a ContentNode node that you configure to contain the data required for the node. 

Configuring a ContentNode Node for Static Content

Generally, you'll want to download dynamic content for your application from your server. But to simply illustrate how to set up a ContentNode node for a node requiring data, the following shows setting a ContentNode node as a child of a LabelList node requiring the data using the role attribute. The example makes clear the hierarchal relationship required for the content field of a LabelList node, with a parent ContentNode node and several child ContentNode nodes for the list item text. The role attribute automatically assigns the ContentNode node to the content field of the LabelList node, and the SceneGraph application shows the text strings in the child ContentNode nodes as the items of the list.

Static ContentNode Node Configuration
  id = "moviemenu"
  translation = "[160,92]"
  itemSize = "[440,48]" > 

  <ContentNode id = "moviemenucontent" role = "content" >

    <ContentNode title = "Comedy" />
    <ContentNode title = "Drama" />
    <ContentNode title = "Action" />
    <ContentNode title = "Horror" />



Configuring a ContentNode Node with Dynamic Content

The ContentNode node can be configured in a Task node when you want to download dynamic data from your server to the ContentNode node. To do this, you must write BrightScript code in the Task node to create the parent ContentNode and the hierarchy of child ContentNode nodes required for your application.

In a Task node, you can use the BrightScript roUrlTransfer component to read the content data from your server. If the data is contained in JSON or XML formats, you can then use the corresponding BrightScript parsing functions and components to configure a ContentNode node with the content data. The BrightScript JSON/XML parsing loop should be set up to terminate when the Task node <interface> field for the target ContentNode node is fully configured with new data, to allow an observeField() function set in the component that requires the data to trigger a callback function to assign the data to the target node.

For example, the following Task node downloads a list of strings to be used as text for a LabelList node. The Task node includes two <interface> fields, one for the URI of the content data (uri), and another for the ContentNode node that will be configured with the data (content). When an XML component requires a list of strings for a LabelList node, the component can set the control field of the Task node object to RUN. This sends the specified <interface> field values to the Task node, in this case the URI of the content data, and starts the Task node. The Task node then downloads an XML file with the content data from the specified URI, parses the XML data, and creates a parent ContentNode node, and child ContentNode nodes for each string. When the ContentNode node is configured with all the strings in the XML file, it is assigned to the ContentNode object reference set in the <interface> field. This change in the field value triggers the observeField() callback function in the component XML file to add the strings to the LabelList node content field.

First, here's the XML file the example Task node downloads from the server and parses:

Example Server XML File
<?xml version = "1.0" encoding = "UTF-8" standalone="yes" ?>


  <item text = "Comedy" />
  <item text = "Drama" />
  <item text = "Action" />
  <item text = "Horror" /> 


And here is how the component XML file configures and starts the Task node process, including setting the observeField() function to trigger a callback function to display the LabelList node after the content data is downloaded:

Example Task Node Configuration and Launch
m.getHomeOptionsList = createObject("roSGNode", "getLabelListContent")
m.getHomeOptionsList.setField("uri", "")
m.getHomeOptionsList.observeField("content", "showhomeoptionslist")
m.getHomeOptionsList.functionName = "showhomeoptionslist"
m.getHomeOptionsList.control = "RUN"

And here's the actual Task node itself that does the work of downloading the server XML file, parsing the XML content data, and configuring a ContentNode node with the data:

Downloading LabelList Node Content
<?xml version = "1.0" encoding = "utf-8" ?>

<!--********** Copyright 2015 Roku Corp.  All Rights Reserved. **********-->

<component name = "getLabelListContent" extends = "Task" >
  <field id = "uri" type = "uri" />
  <field id = "content" type = "node" />

<script type = "text/brightscript" >


  sub init() = "getContent"
  end sub

  sub getContent()
    content = createObject("roSGNode", "ContentNode")
    contentxml = createObject("roXMLElement")

    readInternet = createObject("roUrlTransfer")

    if contentxml.getName() = "listcontent"
      for each item in contentxml.GetNamedElements("item")
        attributes = item.getAttributes()
        item = {
          text: attributes.text
        listitem = content.createChild("ContentNode")
        listitem.title = item.text
      end for
    end if = content
  end sub




Note that this example could be used to download strings for any LabelList node, or for that matter, any node that requires a simple list of strings as the required content for the node. For more complex data requirements, the XML parsing loop in the example could be expanded to include any Content Meta-Data attributes required for the node (and of course, contained in the server XML file).