Defined in List.Def (version 133 Inherits from FixedList
Class DataList is a small subclass of class FixedList that provides you with a convenient way to vary the size of the list's elements. Class FixedList assumes that the list stride is always four; class DataList looks at a stride field to determine what it should be.
Remember that if the documentation and the software (especially the definition files) disagree, always trust the software.
Instantiate: sometimes Subclass: sometimes Call its methods: sometimes
To obtain an object of class DataList, add an instance to an object definition file and edit its fields.
Here's an example of a data list used by an animation object. This list contains a set of speeds corresponding to various behaviors the animation can display:
Instance DataList 9321; // speeds
length: 10;
stride: 8;
entry: <30.0,0.0>; // walk
entry: <100.0,0.0>; // run
entry: <0.0,0.0>; // stop
entry: <0.0,0.0>; // sleep
entry: <0.0,0.0>; // sit down
entry: <0.0,0.0>; // pinch up
entry: <0.0,0.0>; // gesture
entry: <0.0,0.0>; // cry
entry: <1.0,150.0>; // fall
entry: <0.0,0.0>; // wake up
End Instance;
The speeds are of type Dotpairs of long numbers for the vertical and horizontal speed componentsso this list's stride is 8. The following code fragment shows how you might extract data from the sample list shown above.
/* get the object ID of the data list */ ObjectID behaviorSpeeds = Field(self, behaviorSpeeds); Dot speed; /* get a speed from the data list, using ourBehavior as an index into the list */ ElementAt(behaviorSpeeds, ourBehavior, &speed); SetHorizontalSpeed(self, speed.h); SetVerticalSpeed(self, speed.v);
The DataList class has one method you might Call:
| Method | Description |
|---|---|
| Stride | Return the size of a list element |
Whenever you create a subclass of the DataList class, you might want to override the following method:
| Method | When to override |
|---|---|
| Init | Initialize the data list |
The DataList class defines the following fields:
| Field | Type | Description |
|---|---|---|
| Inherited from AbstractList | ||
| length | Unsigned | The number of elements in the list |
| Defined by DataList | ||
| stride | Unsigned | The size in bytes of a list element |
operation Init(VAR newParams: NewDataListParameters) Call: rarely Override: sometimes
When a new object is created, the system calls Init to allow the new object to set up its fields. The params parameter points to a structure containing initial values for the object's fields. In the case of a data list, the structure looks like this:
typedef struct
{
Parameters header;
ulong initialEntries;
ulong stride;
} NewDataListParameters;
Init first sets the stride field to the value in newParams->stride. It then calls its inherited initialization method, passing along the header portion of the parameters.
You should override Init if your data list subclass defines any additional fields that should be initialized when a new instance is created, or if it needs to initialize its inherited fields to values other than the ones shown here. Be sure to include a call to InheritedInit so that the inherited fields are properly set up.
See the description of Object_Init for more information.
field stride: Unsigned, getter; // operation Stride Call: rarely Override: never