I have a shapefile and I want to calculate multiple fields using the GP ValueTable parameter.

The script loads field names from a layer, then I should delete rows I don´t want to calculate and then I should write values to the second column to be filled in selected fields. Then it should ```arcpy.CalculateField```.

But I am stuck at parameter settings. The script lies in the Python toolbox.

    def getParameterInfo(self):
        """Define parameter definitions"""
        param0 = parameter("in_layer", "Vrstva", "GPFeatureLayer")
        param1 = parameter("field_values", "Atributova pole a hodnoty k vyplneni", "GPValueTable")

        param1.parameterDependencies = [param0.name]
        param1.columns = [["String", "Pole"], ["String", "Hodnota"]]

        params = [param0, param1]
        return params

    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."""
        if parameters[0].value:
            v_list = []
            fld_names = [f.name for f in arcpy.ListFields(parameters[0].value)]

            for fld in fld_names:
                v_list.append([fld, ""])
                del fld

            parameters[1].value = v_list

            del fld_names
            del v_list

        return


When I select a layer in the tool, it populates field names (great!) and it looks like this:
[![Tool parameters][1]][1]

But...

 1. If I want to delete some rows using the button on the right side, it does nothing, it does not delete the row. It just seems that it somehow "refreshes" the value table.
 2. If I want to write a value to the second column, it lets me but after hitting enter or clicking anywhere else it erases the written value and sets nothing, empty value again. It does not hold what I am writing there.

  [1]: https://i.sstatic.net/iA0Rn.png