Lifecycle Events

Any capability can observe application lifecycle moments (project open/save, slicing, plate and object edits, preset changes, printer and job activity) by overriding on_lifecycle_event(). It is defined on the root orca.PythonPluginBase, so it is available on every capability type, and the default does nothing.

The payload is deliberately small and generic: it identifies what happened, not the full state. To learn more, call a targeted API from the handler, such as orca.host.plater().model() after an ObjectAdded event (see Host).

import orca

class ProjectWatcher(orca.script.ScriptPluginCapabilityBase):
    def get_name(self): return "Project Watcher"
    def execute(self): return orca.ExecutionResult.success()

    def on_lifecycle_event(self, event, ctx):
        if event == orca.LifecycleEvent.ProjectAfterSave:
            print("saved", ctx.name)
        elif event == orca.LifecycleEvent.SlicingJobComplete and ctx.code == orca.LifecycleEvtCode.Error:
            print("slicing failed:", ctx.msg)

Events

orca.LifecycleEvent values (also exported at module level, e.g. orca.SliceStarted):

Group	Events
Project (3MF)	NewProject, ProjectOpened, ProjectBeforeSave, ProjectAfterSave, ProjectClosed, ProjectDirtyChanged
Slicing	SliceStarted, SliceGeometryFinished, GCodeExportStarted, GCodeExportFinished, SlicingJobComplete
Plate / model editing	ObjectAdded, ObjectDeleted, ObjectTransformed, ObjectChanged, ObjectRenamed, PlateCreated, PlateDeleted, PlateSelected, PlateRenamed
Presets	PresetSelected, PresetSaved
Printer / device	PrintStateChanged, DeviceOnline, DeviceOffline, DeviceDiscovered, DeviceSelected, UploadStarted, UploadFinished
Print / send jobs	PrintJobStarted, PrintJobFinished, SendJobStarted, SendJobFinished

Payload

ctx is an orca.LifecycleEventContext with read-only fields. Fields an event does not use keep their defaults (empty string, index = -1, dirty = False).

Field	Meaning
name	the primary subject: a project/output path, model, object, plate or preset name, device id, upload file name. May be empty
code	orca.LifecycleEvtCode: Ok, Error or Warn. For start and state-change events Ok only means the event occurred
msg	optional human-readable detail; not a stable parsing contract
id	a stable object/model identifier, when the source has one
previous_name	the old name, for rename events
device_id	the device, for print/send job events
job_id	the job/task identifier, when the originating queue provides one
source	the originating subsystem or operation, suitable for filtering
index	a plate, object or volume index, when the source uses one
dirty	the aggregate project dirty state, for ProjectDirtyChanged

What the current sources fill in:

Event	Payload
NewProject	no subject; only code
ProjectOpened, ProjectBeforeSave, ProjectAfterSave, ProjectClosed	name = project file / project name
ProjectDirtyChanged	dirty, source
SliceStarted, SliceGeometryFinished	id = model id, name = model name
GCodeExportStarted, GCodeExportFinished	id, name, msg = output path; on failure code = Error and msg also carries the error
SlicingJobComplete	id, name; code is Warn with msg = "cancelled" when cancelled, Error with the error text on failure
ObjectAdded, ObjectDeleted	name = object name
ObjectTransformed	msg = moved, rotated, scaled, arranged or auto_oriented; name for interactive moves/rotations/scales
ObjectChanged	name, id, source = "geometry" (and index when known)
ObjectRenamed	name, previous_name, id, index, source = object or volume
PlateCreated, PlateDeleted, PlateSelected	name = plate name, index = plate index
PlateRenamed	name, previous_name, index
PresetSelected	name = preset, msg = preset type (print, filament, printer, ...)
PresetSaved	name = preset, msg = new or overwrite
PrintStateChanged	name = device id, msg = new print status
DeviceOnline, DeviceOffline, DeviceDiscovered, DeviceSelected	name = device id
UploadStarted, UploadFinished	name = uploaded file name; on failure code = Error, msg = error
PrintJobStarted, PrintJobFinished, SendJobStarted, SendJobFinished	name = project name, device_id, source (print_job, send_job or task_manager), job_id for task-manager jobs; a finished job reports Warn/cancelled or Error

Use the table as a guide, not a contract: rely on event and code, and treat a missing field as "not provided".

Delivery Rules

• Every loaded and enabled capability of every plugin receives every event, regardless of capability type. Disabled capabilities are skipped.
• Events are delivered synchronously on the thread that raised them: typically the UI thread for editing, project and preset events, the slicing worker for the slicing and G-code export events, and job/upload worker threads for job and upload events. Do not assume the UI thread, keep handlers short, and never block: the slicer waits for your handler to return. A print task's PrintJobStarted and PrintJobFinished arrive on the same worker thread.
• Once a slice is cancelled, dispatch of its slicing and G-code export events stops before the next capability is called.
• An exception raised by a handler is logged (with the event and payload) and swallowed; it does not affect OrcaSlicer or the other plugins.
• Handlers run inside an audit context like any other plugin call, so filesystem, network and process access prompts the user. See Plugin Audit Hook.
• When plugins shut down, OrcaSlicer stops accepting new events and waits for handlers already running to finish before unloading plugin code.

See Registry for the other members every capability inherits.