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Tip: Using decorators to manage handlers

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Tip: Using decorators to manage handlers

I don't know about you, but I found working with and managing handlers to be a little cumbersome.  So I've written a python decorator that I believe makes working with handlers much easier (it does for me, at least).  It's not fully tested, but so far it's worked on everything I've tried it on - I'm sure you'll let me know if there any issues.


So if you're interested read on:


You can find several approaches to attaching and managing handlers in the API reference and other places, but AFAIK I've not seen an approach using decorators, so I'm providing my solution in the hope that it could/will help someone.


The way I use this is:


#just in front of the handler
@eventHandler(handler_cls = adsk.core.CommandEventHandler)
def CreateExecuteHandler(eventArgs: adsk.core.CommandEventArgs):
    .... body of the handler function



in the code where you want to attach the handler


CreateExecuteHandler(event = cmd.execute)


 where, the references for handler_cls, event and eventArgs are associated with the particular event you want to attach (eg handler_cls: adsk.core.DocumentEventHandler, eventArgs: adsk.core.DocumentEventArgs and event: documentEvent_var etc.)


If you need to delete the handlers, I've included a groupId:str option



@eventHandler(handler_cls = adsk.core.CommandEventHandler, groupId = 'xyz')




HandlerCollection.remove(groupId =  'xyz')


 Note: the HandlerCollection needs to be imported separately  from the module  (There may be a better way to do this, I'll make it available if I figure it out)


HandlerCollection.remove() #without any parameters, will delete all the handlers



I think this is so much easier to  read than:


_handlers = []  

def someFunction():
   global _handlers
   onExecute = CreateExecuteHandler()

class CreateExecuteHandler(adsk.core.CommandEventHandler):
    def __init__(self):
    def notify(self, args):
            eventArgs = adsk.core.CommandEventArgs.cast(args)        
            .... rest of the handler code


and this doesn't event start to address handler deletion


If this is of interest to anyone I've attached the file.  Below (also attached) is the commandInputsSample modified with the decorator (original file available here)   



#Author-Autodesk Inc.
#Description-Demo command input examples
import adsk.core, adsk.fusion, traceback
from .decorators import eventHandler
_app = None
_ui  = None
_rowNumber = 0

# Adds a new row to the table.
def addRowToTable(tableInput):
    global _rowNumber
    # Get the CommandInputs object associated with the parent command.
    cmdInputs = adsk.core.CommandInputs.cast(tableInput.commandInputs)
    # Create three new command inputs.
    valueInput = cmdInputs.addValueInput('TableInput_value{}'.format(_rowNumber), 'Value', 'cm', adsk.core.ValueInput.createByReal(_rowNumber))
    stringInput =  cmdInputs.addStringValueInput('TableInput_string{}'.format(_rowNumber), 'String', str(_rowNumber))
    spinnerInput = cmdInputs.addIntegerSpinnerCommandInput('spinnerInt{}'.format(_rowNumber), 'Integer Spinner', 0 , 100 , 2, int(_rowNumber))
    # Add the inputs to the table.
    row = tableInput.rowCount
    tableInput.addCommandInput(valueInput, row, 0)
    tableInput.addCommandInput(stringInput, row, 1)
    tableInput.addCommandInput(spinnerInput, row, 2)
    # Increment a counter used to make each row unique.
    _rowNumber = _rowNumber + 1

def updateSliders(sliderInputs):
    Populate 'slider_configuration' group with as many sliders as set in 'slider_controller'.
    Delete previous ones and create new sliders.
    spinner = sliderInputs.itemById("slider_controller")
    value = spinner.value
    # check ranges
    if value > spinner.maximumValue or value < spinner.minimumValue:

    # delete all sliders we have
    toRemove = []
    for i in range(sliderInputs.count):
        input = sliderInputs.item(i)
        if input.objectType == adsk.core.FloatSliderCommandInput.classType():
    for input in toRemove:

    # create new ones with range depending on total number
    for i in range(1, value+1):
        id = str(i)
        sliderInputs.addFloatSliderCommandInput("slider_configuration_" + id, "slider_" + id, "cm", 0, 10.0*value)

# Event handler that reacts to any changes the user makes to any of the command inputs.
@eventHandler(handler_cls= adsk.core.InputChangedEventHandler)
def MyCommandInputChangedHandler(eventArgs:adsk.core.InputChangedEventArgs):
        inputs = eventArgs.inputs
        cmdInput = eventArgs.input
        # onInputChange for slider controller
        if == "slider_controller":
            sliderGroup = adsk.core.GroupCommandInput.cast(cmdInput.parentCommandInput)
            sliderInputs = sliderGroup.children
            tableInput = inputs.itemById('table')
            if == 'tableAdd':
            elif == 'tableDelete':
                if tableInput.selectedRow == -1:
                    _ui.messageBox('Select one row to delete.')

# Event handler that reacts to when the command is destroyed. This terminates the script.            
@eventHandler(handler_cls = adsk.core.CommandEventHandler)
def MyCommandDestroyHandler(args):
        # When the command is done, terminate the script
        # This will release all globals which will remove all event handlers

# Event handler that reacts when the command definitio is executed which
# results in the command being created and this event being fired.
@eventHandler(handler_cls = adsk.core.CommandCreatedEventHandler)
def MyCommandCreatedHandler(args):

        cmd:adsk.core.Comm = args.command
        # Connect to the command destroyed event.
        MyCommandDestroyHandler(event = cmd.destroy)

        # Connect to the input changed event.           
        MyCommandInputChangedHandler(event = cmd.inputChanged)

        # Get the CommandInputs collection associated with the command.
        inputs = cmd.commandInputs

        # Create a tab input.
        tabCmdInput1 = inputs.addTabCommandInput('tab_1', 'Tab 1')
        tab1ChildInputs = tabCmdInput1.children

        # Create a read only textbox input.
        tab1ChildInputs.addTextBoxCommandInput('readonly_textBox', 'Text Box 1', 'This is an example of a read-only text box.', 2, True)

        # Create an editable textbox input.
        tab1ChildInputs.addTextBoxCommandInput('writable_textBox', 'Text Box 2', 'This is an example of an editable text box.', 2, False)
        # Create a message that spans the entire width of the dialog by leaving out the "name" argument.
        message = '<div align="center">A "full width" message using <a href="">html.</a></div>'
        tab1ChildInputs.addTextBoxCommandInput('fullWidth_textBox', '', message, 1, True)            

        # Create a selection input.
        selectionInput = tab1ChildInputs.addSelectionInput('selection', 'Select', 'Basic select command input')

        # Create a string value input.
        strInput = tab1ChildInputs.addStringValueInput('string', 'Text', 'Basic string command input')

        # Create value input.
        tab1ChildInputs.addValueInput('value', 'Value', 'cm', adsk.core.ValueInput.createByReal(0.0))

        # Create bool value input with checkbox style.
        tab1ChildInputs.addBoolValueInput('checkbox', 'Checkbox', True, '', False)

        # Create bool value input with button style that can be clicked.
        tab1ChildInputs.addBoolValueInput('buttonClick', 'Click Button', False, 'resources/button', True)

        # Create bool value input with button style that has a state.
        tab1ChildInputs.addBoolValueInput('buttonState', 'State Button', True, 'resources/button', True)

        # Create float slider input with two sliders.
        tab1ChildInputs.addFloatSliderCommandInput('floatSlider', 'Float Slider', 'cm', 0, 10.0, True)

        # Create float slider input with two sliders and a value list.
        floatValueList = [1.0, 3.0, 4.0, 7.0]
        tab1ChildInputs.addFloatSliderListCommandInput('floatSlider2', 'Float Slider 2', 'cm', floatValueList)

        # Create float slider input with two sliders and visible texts.
        floatSlider3 = tab1ChildInputs.addFloatSliderCommandInput('floatSlider3', 'Float Slider 3', '', 0, 50.0, False)
        floatSlider3.setText('Min', 'Max')

        # Create integer slider input with one slider.
        tab1ChildInputs.addIntegerSliderCommandInput('intSlider', 'Integer Slider', 0, 10);
        valueList = [1, 3, 4, 7, 11]

        # Create integer slider input with two sliders and a value list.
        tab1ChildInputs.addIntegerSliderListCommandInput('intSlider2', 'Integer Slider 2', valueList)

        # Create float spinner input.
        tab1ChildInputs.addFloatSpinnerCommandInput('spinnerFloat', 'Float Spinner', 'cm', 0.2 , 9.0 , 2.2, 1)

        # Create integer spinner input.
        tab1ChildInputs.addIntegerSpinnerCommandInput('spinnerInt', 'Integer Spinner', 2 , 9 , 2, 3)

        # Create dropdown input with checkbox style.
        dropdownInput = tab1ChildInputs.addDropDownCommandInput('dropdown', 'Dropdown 1', adsk.core.DropDownStyles.CheckBoxDropDownStyle)
        dropdownItems = dropdownInput.listItems
        dropdownItems.add('Item 1', False, 'resources/One')
        dropdownItems.add('Item 2', False, 'resources/Two')

        # Create dropdown input with icon style.
        dropdownInput2 = tab1ChildInputs.addDropDownCommandInput('dropdown2', 'Dropdown 2', adsk.core.DropDownStyles.LabeledIconDropDownStyle);
        dropdown2Items = dropdownInput2.listItems
        dropdown2Items.add('Item 1', True, 'resources/One')
        dropdown2Items.add('Item 2', False, 'resources/Two')

        # Create dropdown input with radio style.
        dropdownInput3 = tab1ChildInputs.addDropDownCommandInput('dropdown3', 'Dropdown 3', adsk.core.DropDownStyles.LabeledIconDropDownStyle);
        dropdown3Items = dropdownInput3.listItems
        dropdown3Items.add('Item 1', True, '')
        dropdown3Items.add('Item 2', False, '')

        # Create dropdown input with test list style.
        dropdownInput4 = tab1ChildInputs.addDropDownCommandInput('dropdown4', 'Dropdown 4', adsk.core.DropDownStyles.TextListDropDownStyle);
        dropdown4Items = dropdownInput4.listItems
        dropdown4Items.add('Item 1', True, '')
        dropdown4Items.add('Item 2', False, '')

        # Create single selectable button row input.
        buttonRowInput = tab1ChildInputs.addButtonRowCommandInput('buttonRow', 'Single Select Buttons', False)
        buttonRowInput.listItems.add('Item 1', False, 'resources/One')
        buttonRowInput.listItems.add('Item 2', False, 'resources/Two')

        # Create multi selectable button row input.
        buttonRowInput2 = tab1ChildInputs.addButtonRowCommandInput('buttonRow2', 'Multi-select Buttons', True)
        buttonRowInput2.listItems.add('Item 1', False, 'resources/One')
        buttonRowInput2.listItems.add('Item 2', False, 'resources/Two')

        # Create tab input 2
        tabCmdInput2 = inputs.addTabCommandInput('tab_2', 'Tab 2')
        tab2ChildInputs = tabCmdInput2.children

        # Create group input.
        groupCmdInput = tab2ChildInputs.addGroupCommandInput('group', 'Group')
        groupCmdInput.isExpanded = True
        groupCmdInput.isEnabledCheckBoxDisplayed = True
        groupChildInputs = groupCmdInput.children
        # Create radio button group input.
        radioButtonGroup = groupChildInputs.addRadioButtonGroupCommandInput('radioButtonGroup', 'Radio button group')
        radioButtonItems = radioButtonGroup.listItems
        radioButtonItems.add("Item 1", False)
        radioButtonItems.add("Item 2", False)
        radioButtonItems.add("Item 3", False)
        # Create image input.
        groupChildInputs.addImageCommandInput('image', 'Image', "resources/image.png")
        # Create direction input 1.
        directionCmdInput = tab2ChildInputs.addDirectionCommandInput('direction', 'Direction1')
        directionCmdInput.setManipulator(adsk.core.Point3D.create(0, 0, 0), adsk.core.Vector3D.create(1, 0, 0))
        # Create direction input 2.
        directionCmdInput2 = tab2ChildInputs.addDirectionCommandInput('direction2', 'Direction 2', 'resources/One')
        directionCmdInput2.setManipulator(adsk.core.Point3D.create(0, 0, 0), adsk.core.Vector3D.create(0, 1, 0)) 
        directionCmdInput2.isDirectionFlipped = True
        # Create distance value input 1.
        distanceValueInput = tab2ChildInputs.addDistanceValueCommandInput('distanceValue', 'DistanceValue', adsk.core.ValueInput.createByReal(2))
        distanceValueInput.setManipulator(adsk.core.Point3D.create(0, 0, 0), adsk.core.Vector3D.create(1, 0, 0))
        distanceValueInput.minimumValue = 0
        distanceValueInput.isMinimumValueInclusive = True
        distanceValueInput.maximumValue = 10
        distanceValueInput.isMaximumValueInclusive = True
        # Create distance value input 2.
        distanceValueInput2 = tab2ChildInputs.addDistanceValueCommandInput('distanceValue2', 'DistanceValue 2', adsk.core.ValueInput.createByReal(1))
        distanceValueInput2.setManipulator(adsk.core.Point3D.create(0, 0, 0), adsk.core.Vector3D.create(0, 1, 0))
        distanceValueInput2.expression = '1 in'
        distanceValueInput2.hasMinimumValue = False
        distanceValueInput2.hasMaximumValue = False
        # Create table input
        tableInput = tab2ChildInputs.addTableCommandInput('table', 'Table', 3, '1:1:1')

        # Add inputs into the table.            
        addButtonInput = tab2ChildInputs.addBoolValueInput('tableAdd', 'Add', False, '', True)
        deleteButtonInput = tab2ChildInputs.addBoolValueInput('tableDelete', 'Delete', False, '', True)
        # Create angle value input.
        angleValueInput = tab2ChildInputs.addAngleValueCommandInput('angleValue', 'AngleValue', adsk.core.ValueInput.createByString('30 degree'))
        angleValueInput.setManipulator(adsk.core.Point3D.create(0, 0, 0), adsk.core.Vector3D.create(1, 0, 0), adsk.core.Vector3D.create(0, 0, 1))
        angleValueInput.hasMinimumValue = False
        angleValueInput.hasMaximumValue = False

        # Create tab input 3
        tabCmdInput3 = inputs.addTabCommandInput('tab_3', 'Tab 3')
        tab3ChildInputs = tabCmdInput3.children
        # Create group
        sliderGroup = tab3ChildInputs.addGroupCommandInput("slider_configuration", "Configuration")
        sliderInputs = sliderGroup.children
        # Create integer spinner input
        sliderInputs.addIntegerSpinnerCommandInput("slider_controller", "Num sliders", 1, 5, 1, 1)

def run(context):
        global _app, _ui
        _app = adsk.core.Application.get()
        _ui = _app.userInterface

        # Get the existing command definition or create it if it doesn't already exist.
        cmdDef = _ui.commandDefinitions.itemById('cmdInputsSample')
        if not cmdDef:
            cmdDef = _ui.commandDefinitions.addButtonDefinition('cmdInputsSample', 'Command Inputs Sample', 'Sample to demonstrate various command inputs.')

        # Connect to the command created event.
        MyCommandCreatedHandler(event = cmdDef.commandCreated)

        # Execute the command definition.

        # Prevent this module from being terminated when the script returns, because we are waiting for event handlers to fire.
        if _ui:



I hope this helps someone.




I'm not an expert, but I know enough to be very, very dangerous.

Life long R&D Engineer (retired after 30+ years in Military Communications, Aerospace Robotics and Transport Automation).
Message 2 of 2
in reply to: pludikar

Thank you @pludikar a lot, this will be very helpful to me. 

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