Table of Contents
Instances of components defined in an XML file follow a well-defined initialization order when they are created.
The <children> element nodes defined in XML markup are created, and their fields are set to their initial values, either to a default value, or to the value specified in the XML markup.
The <interface> element fields of the XML component are created, and their initial values are set, either to a default value, or to the value specified by the
valueattribute.The <script> element
init()function is called, and all initializations contained in the function are performed.
Note the following implications of this initialization order.
Initial XML Markup Node Field Values May Be Overridden
The field values defined in XML markup in the <children> nodes may be overridden as many as two times, depending on the definitions of the <interface> element field attributes, and the initializations contained in the <script> element init() function.
Observer Functions
Observer functions of fields that are set up in the init() function do not get called when those fields are initialized. This is because the initialization of interface fields, or of fields of the component <children> element nodes, is done before the init() function that sets up the observers is called. Thus, in some cases, it may be necessary to explicitly call the field observer functions in init() if they need to be executed for the initial field setting.
Also note that field observer callback functions set up in init() cannot be guaranteed to have returned when the component is created using createObject() or createChild(). This means that a component object may not have been completely constructed immediately after those calls. For certain nodes that may rely on dynamically-downloaded content to construct the node, such as PosterGrid, subsequent object function calls may return an object reference to an unconstructed object.
Parenting and the Focus Chain
For nodes that are defined in the <children> XML markup of the component file, the parent node is set after the node is created, and init() is called. This has implications for the focus chain (see Remote Control Events), which must end at a node derived from Scene. Until the newly-created node is parented to a node that is either derived from Scene, or parented to a node in a focus chain that ends on a node derived from Scene, you will not be able to set remote control focus on the node.
Program Action Fields
Certain fields should not be set in XML markup of the SceneGraph nodes, specifically any control fields that initiate a program action, such as starting a video to play, or an animation. These fields should be set in BrightScript as part of scripting the program flow of the component.