core.utilities / ProgressTracker

# ProgressTracker

`class ProgressTracker`

A progress tracker helps surface information about the progress of an operation to a user interface or API of some kind. It lets you define a set of <emph>steps</emph> that represent an operation. A step is represented by an object (typically a singleton).

Steps may logically be children of other steps, which models the case where a large top level operation involves sub-operations which may also have a notion of progress. If a step has children, then the tracker will report the steps children as the "next step" after the parent. In other words, a parent step is considered to involve actual reportable work and is a thing. If the parent step simply groups other steps, then youll have to step over it manually.

Each step has a label. It is assumed by default that the label does not change. If you want a label to change, then you can emit a ProgressTracker.Change.Rendering object on the ProgressTracker.Step.changes observable stream after it changes. That object will propagate through to the top level trackers changes stream, which renderers can subscribe to in order to learn about progress.

An operation can move both forwards and backwards through steps, thus, a ProgressTracker can represent operations that include loops.

A progress tracker is <emph>not</emph> thread safe. You may move events from the thread making progress to another thread by using the Observable subscribeOn call.

### Types

Change | `sealed class Change`
DONE | `object DONE : Step`
RelabelableStep | `inner class RelabelableStep : Step` This class makes it easier to relabel a step on the fly, to provide transient information.
Step | `class Step` The superclass of all step objects.
UNSTARTED | `object UNSTARTED : Step`

### Constructors

<init> | `ProgressTracker(vararg steps: Step)` A progress tracker helps surface information about the progress of an operation to a user interface or API of some kind. It lets you define a set of <emph>steps</emph> that represent an operation. A step is represented by an object (typically a singleton).

### Properties

allSteps | `val allSteps: List<<ERROR CLASS><Int, Step>>` A list of all steps in this ProgressTracker and the children, with the indent level provided starting at zero. Note that UNSTARTED is never counted, and DONE is only counted at the calling level.
changes | `val changes: <ERROR CLASS><Change>` An observable stream of changes: includes child steps, resets and any changes emitted by individual steps (e.g. if a step changed its label or rendering).
childrenFor | `var childrenFor: HashMap<Step, ProgressTracker>` Writable map that lets you insert child ProgressTrackers for particular steps. Its OK to edit this even after a progress tracker has been started.
currentStep | `var currentStep: Step` Reading returns the value of stepsstepIndex, writing moves the position of the current tracker. Once moved to the DONE state, this tracker is finished and the current step cannot be moved again.
currentStepRecursive | `val currentStepRecursive: Step` Returns the current step, descending into children to find the deepest step we are up to.
parent | `var parent: ProgressTracker?` The parent of this tracker: set automatically by the parent when a tracker is added as a child
stepIndex | `var stepIndex: Int` The zero-based index of the current step in the steps array (i.e. with UNSTARTED and DONE)
steps | `val steps: Array<Step>` The steps in this tracker, same as the steps passed to the constructor but with UNSTARTED and DONE inserted.
topLevelTracker | `val topLevelTracker: ProgressTracker` Walks up the tree to find the top level tracker. If this is the top level tracker, returns this

### Functions

nextStep | `fun nextStep(): Step` Iterates the progress tracker. If the current step has a child, the child is iterated instead (recursively). Returns the latest step at the bottom of the step tree.