called when the task has completed (successfully or otherwise).
This allows for simpler task design when the signal/slot
based approach is not required. Just implement run() with your
heavy lifting, and finished() to do whatever follow up stuff
should happen after the task is complete. finished is always
called from the main thread, so it's safe to do GUI operations
here.
Python based tasks using the simplified QgsTask.fromFunction
approach can now set a on_finished argument to a function
to call when the task is complete.
eg:
def calculate(task):
# pretend this is some complex maths and stuff we want
# to run in the background
return 5*6
def calculation_finished(result, value=None):
if result == QgsTask.ResultSuccess:
iface.messageBar().pushMessage(
'the magic number is {}'.format(value))
elif result == QgsTask.ResultFail:
iface.messageBar().pushMessage(
'couldn\'t work it out, sorry')
task = QgsTask.fromFunction('my task', calculate,
on_finished=calculation_finished)
QgsTaskManager.instance().addTask(task)
Multiple values can also be returned, eg:
def calculate(task):
return (4, 8, 15)
def calculation_finished(result, count=None, max=None, sum=None):
# here:
# count = 4
# max = 8
# sum = 15
task = QgsTask.fromFunction('my task', calculate,
on_finished=calculation_finished)
QgsTaskManager.instance().addTask(task)
QgsTask subclasses can now return a result (success or fail)
directly from QgsTask::run. If they do so then there's no
need for them to manually call completed() or stopped()
to report their completion.
Alternatively, tasks can also return the ResultPending value
to indicate that the task is still operating and will
manually report its completion by calling completed() or
stopped(). This may be useful for tasks which rely on external
events for completion, eg downloading a file. In this case
Qt slots could be created which are connected to the download
completion or termination and which call completed() or
stopped() to indicate the task has finished operations.
above a layout.
Supports setting another widget as a anchor point for the widget, eg
the floating widget could be set so that it's always placed to the
top-right of the anchor widget.
Adds new classes:
- QgsTask. An interface for long-running background tasks
- QgsTaskManager. Handles groups of tasks - also available as a global
instance for tracking application wide tasks
- QgsTaskManagerWidget. A list view for showing active tasks and their
progress, and for cancelling them
A new dock widget has been added with a task manager widget showing
global tasks
Replaces the existing 'Basic Stats for Numeric Fields' and
'Basic Stats for String Fields' algorithms and adds support
for date/time/datetime fields.
Having a single unified algorithm allows more flexible models
where a field type may not be known in advance.
Deprecate existing basic stats algorithms
