Table of Contents
SceneGraph applications have data object scoping rules that are similar to traditional programming languages. You have:
- function scope: objects that can only be accessed within the function in which they were defined
- component scope: objects that can be accessed anywhere within a component XML file, similar to file scope in traditional programming languages
- global scope: objects that can be accessed anywhere within a SceneGraph application
These different levels of scoping are identified by the use of the m
object reference which can be used to disambiguate and access objects at different levels, similar to the use of m
in BrightScript.
Function Scope
For creating objects with function scope, do not use the m
object reference. For example, the following creates and defines several fields for a dialog
object that can only be accessed within the function in which it is created and defined:
dialog = createObject("RoSGNode","Dialog")
dialog.backgroundUri = "pkg:/images/sgetdialogbg.9.png"
dialog.title = "Example Dialog"
dialog.optionsDialog = true
dialog.message = "Press * To Dismiss"
Component Scope
For creating objects with component scope, use the m
object reference to identify objects that can be accessed anywhere within a component XML file. For example, if you wanted to create the same dialog
object above in one function, but define it, or otherwise access it, in another function in the same component XML file:
sub createdialog()
m.dialog = createObject("RoSGNode","Dialog")
end sub
sub definedialog()
m.dialog.backgroundUri = "pkg:/images/sgetdialogbg.9.png"
m.
dialog.title = "Example Dialog"
m.
dialog.optionsDialog = true
m.
dialog.message = "Press * To Dismiss"
end sub
m.top Component Scope Reference
There is a special use of the m
object reference in SceneGraph for identifying the top of the SceneGraph tree for a component XML file. To do this, use the m.top
object reference, which refers to the component itself. For example, to create the dialog
object and assign it to the dialog
field of a Scene node defined in a component XML file (which is the required usage of the Dialog node class), assign the dialog
object to the dialog
field using the m.top
object reference:
dialog = createObject("RoSGNode","Dialog")
dialog.backgroundUri = "pkg:/images/sgetdialogbg.9.png"
dialog.title = "Example Dialog"
dialog.optionsDialog = true
dialog.message = "Press * To Dismiss"
m.top.dialog = dialog
Likewise, if you want to use findNode()
to find a SceneGraph node object anywhere in the SceneGraph tree for a component XML file, use the m.top
reference to start at the top of the tree:
m.categorieslist = m.top.findNode("categorieslist")
Global Scope
Rules
- To declare a data object at global scope, store it in a field or child of the global node. This global node may be accessed from the entire SceneGraph application.
- To access the global node in components, use the predefined
m.global
, much likem.top
. - For access to the global node from non-component script as in
source/main.brs
, usegetGlobalNode()
called on theroSGScreen
object. - In non-component script, where the global node is obtained using
getGlobalNode()
, you can store it inm.global
so that the syntax for subsequent references to it matches that for components.
For example:
screen = CreateObject("roSGScreen") m.port = CreateObject("roMessagePort") screen.setMessagePort(m.port) m.global = screen.getGlobalNode() m.global.id = "GlobalNode"
As noted, this is not necessary in component script, as m.global
is predefined.
You can access and set the fields, or the children nodes, of the global node from anywhere in the SceneGraph application. In the non-component example above, the global node id
field value is set to GlobalNode
. Likewise, you can access and set the fields for the global node from components by accessing the component m
to get its special global element:
m.global.addFields( {red: &hff0000ff, green: &h00ff00ff, blue: &h0000ffff} ) ... m.rect = m.top.findNode("Rect1") m.rect.color = m.global.red ... color = m.rect.color if m.rect.color = m.global.red m.rect.color = m.global.green else if m.rect.color = m.global.green m.rect.color = m.global.blue else m.rect.color = m.global.red end if