Get the features count of a GPFeatureRecordSetLayer before execute python script tool

Question

I am trying to get the count of features in a GPFeatureRecordSetLayer parameter before executing the tool. By using the arcpy.GetCount_management tool I am getting 0 all the times (see code below). I have also tried to use the JSON property of the input FeatureSet but still with no success. Running the arcpy.GetCount_management tool in Execute method of the tool gives me the correct number but I need it before that so I can use it for validation. Is there a way to get the features count of a GPFeatureRecordSetLayer parameter and use it to add an error message to the parameter if the count is greater than 1?

import arcpy

class Toolbox(object):

    def __init__(self):
        """Define the toolbox (the name of the toolbox is the name of the
        .pyt file)."""
        self.label = "Toolbox"
        self.alias = ""

        # List of tool classes associated with this toolbox
        self.tools = [Tool]

class Tool(object):

    def __init__(self):
        """Define the tool (tool name is the name of the class)."""
        self.label = "InteractiveInput"
        self.description = "Test Interactive Input"
        self.canRunInBackground = False

    def getParameterInfo(self):
        params = []

        prmInPolygon = arcpy.Parameter(
            displayName='Interactive Polygon',
            name='inPolygon',
            datatype="GPFeatureRecordSetLayer",
            parameterType="Required",
            direction="Input")
        #replace with a valid template
        prmInPolygon.value = r"C:\\template.lyr"
        params.append(prmInPolygon)

        prmDebug1 = arcpy.Parameter(
            displayName="Debug 1",
            name="debug1",
            datatype="GPString",
            parameterType="Optional",
            direction="Input")
        params.append(prmDebug1)

        return params


    def isLicensed(self):
        """Set whether tool is licensed to execute."""
        return True

    def updateParameters(self, parameters):
        """Modify the values and properties of parameters before internal
        validation is performed.  This method is called whenever a parameter
        has been changed."""
        result = arcpy.GetCount_management(parameters[0].valueAsText)
        count = int(result.getOutput(0))
        parameters[1].value = count

        return


    def updateMessages(self, parameters):
        """Modify the messages created by internal validation for each tool
        parameter.  This method is called after internal validation."""
        return

    def execute(self, parameters, messages):
        """The source code of the tool."""
        return

Answer 1

It looks like the GetCount tool doesn’t work because the updateParameters is not triggered. When another parameter is changed, and the updateParameters function is called, the GetCount returns the correct value (it doesn't take into consideration any selected features). This means that no matter what are the edits for a GPFeatureRecordSetLayer parameter, the updateParameters is not called (even if you press Editor>Save edits).