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Parameter Node Wrapper

Key Investigators

Project Description

Best practice when writing new ScriptedLoadableModules is to use a “parameter node” to store state (most commonly the state of the GUI). However, the existing parameter node system was in essence a string to string map (which some exceptions regarding storing MRML node references), while many times the state should not logically be a string.

A wrapper system was created, the parameterNodeWrapper, to allow better typed access to parameter nodes. This system allows using many Python built-ins by default, and is extensible for custom classes.

Because the parameterNodeWrapper uses type annotations, automatic connections can also be made to GUI components.


import enum
from slicer.parameterNodeWrapper import parameterNodeWrapper

class ConversionMethods(enum.Enum):
    AVERAGE = 2

class VectorToScalarVolumeParameterNode:
    InputVolume: slicer.vtkMRMLVectorVolumeNode
    OutputVolume: slicer.vtkMRMLScalarVolumeNode
    ConversionMethod: ConversionMethods
    ComponentToExtract: int

class VectorToScalarVolumeWidget(ScriptedLoadableModuleWidget):
  def setup(self):
    self._parameterNode = VectorToScalarVolumeParameterNode(self.logic.getParameterNode())
  def updateParameterNodeFromGUI(self, caller=None, event=None):
    # Modify all properties in a single batch
    with slicer.util.NodeModify(self._parameterNode):
      self._parameterNode.InputVolume = self.ui.inputSelector.currentNode()
      self._parameterNode.OutputVolume = self.ui.outputSelector.currentNode()
      self._parameterNode.ConversionMethod = self.ui.methodSelectorComboBox.currentData
      self._parameterNode.ComponentToExtract = self.ui.componentsSpinBox.value
  def onApplyButton(self):


  1. Work on automatic GUI creation from a parameterNodeWrapper.
  2. Create examples/templates/documentation on how to use the parameterNodeWrapper functionality.
  3. Determine new features.
  4. Implement new features as able.

Approach and Plan

  1. Describe specific steps of what you plan to do to achieve the above described objectives.

Progress and Next Steps

  1. Added ability to use the typing.Any annotation in the parameter node wrapper, with some limitations.
  2. Added automatic gui generation for the parameterNodeWrapper (PR coming soon).
  3. Bug fixes.


Background and References