The SceneGraph Developer Extension's (SGDEX) Content Manager simplifies task management for developers by using a Content Handler to view as well as manage the Task Nodes, and streamline the multi-threaded nature of Roku SceneGraph Nodes.
In order to populate a view, the developer needs to provide the Content Manager with config data to drive that view's Content Getter(s).
Content Handlers (CH) are responsible for all content loading tasks in SGDEX. Channels typically extend ContentHandler to implement specific content or data loading tasks. ContentHandlers should implement a function called
GetContent(). This function is called by SGDEX, allowing the handler to make application specific API calls or perform other operations to load the content associated with the handler.
CHs modify the Content Node referenced by
m.top.content to get the content
A Content Handler is made up of two components; Markup, and BrightScript. A very simple CH might look like the following:
Content Getter Handler Config
Each CH is driven by a Content Handler Config (CHConfig). The CHConfig is set as the value of a field on the content node that needs to be modified. The simplest CHConfig consists of the name of the component that implements it. The example below defines a
DetailView CHConfig that invokes the simple CH defined above:
Grid View Supported Data Models
In a single task model, all the data for the grid is populated by a single CH. The CHConfig for this CH should be placed in the
GridView's root Content node.
One Task Per Row
In this model, the rows of a grid are defined by a root CH similar to the single task model, but the content for each row is populated by a separate CH. To accomplish this, each row that requires loading content has its own CHConfig. It can be set either in the root CH or in other CH.
Multiple Tasks Per Row
This model is useful when the developer is working with an API that returns the content of a row in pages and each page requires a separate API call. There are two variations of this model.
In the serial variation, the pages of content of a row must be requested in order.
To implement this, the root CH places a CHConfig on each of its child nodes (that represent a row), as in the "One Task Per Row" model. Moreover, the CHConfig rows have a field
hasMore that tells SGDEX that the row has more items to load. This CH is invoked by SGDEX multiple times without deleting the CHConfig. When a developer loads portion serial content and is aware of more content that exists, they can set a new CH to
m.top.content inside of the
In the non-serial variation, the pages of content of a row can be requested out of order. The developer must know from the beginning how many items are there in each row altogether.
The implementation of this model is complex. To implement this model, the root CH places a CHConfig on each of its child nodes (that represent a row), as in the "One Task Per Row" model.
When SGDEX invokes a row's initial CH, it deletes the CHConfig. The initial CH does two things:
Populate the row with "n" placeholder content items where n is the final number of items the row contains
Place a new CHConfig on the row's node with a
pageSize field, similar to that in the serial model
SGDEX then calls this secondary row CH multiple times, without deleting the CHConfig. Each time it is called, the CH updates the appropriate placeholder items on the row with the final content. Note that the CH uses the values found in
m.top.pageSize to determine which items it needs to update.
In some cases, when SGDEX invokes a CH, it deletes the associated CHConfig. But the developer may need to re-run a CH.
One such instance is when an API request fails. In this case, the recommended approach is for the CH to detect the error and then set
m.top.failed = true in the
If the developer needs to invoke another handler, they can specify a new CHConfig on the same Content node passed by SGDEX to
m.top.content and filed in the Content handler; Otherwise, the old CHConfig will be used. This causes SGDEX to invoke the CH defined by the new CHConfig so the request can be re-tried.
DetailsView supported Data Models
If the channel does not have content to show on the details view and needs to load it via an API call, set the
HandlerConfigDetails to a content node in the details view. This CH has a basic structure (See: Content Handler Config).
Details view supports two variants for using content; List model and Single model. List model is used to show the list of items on details view and the user can navigate right/left to switch them. A single model is a details view that displays only one item.
This is the default data model for DetailsView.
To load the list of items to be displayed in a details view, set a
HandlerConfigDetails on the view's root Content node. Then, in the CH's
GetContent() function, append the children to
m.top.content for each of the items to be displayed.
Single Item Model
To display a single item in a DetailsView, set a single Content node to the view's content field:
view.isContentList = false