How to select all values by default in arcgis tool's multivalue parameter using python?

Question

I am using ArcGIS 10.2 and have three parameters, Feature class, field and a multivalue parameter respectively in ArcGIS tool. I populate multivalue parameter with unique values of feature class on selection of feature class and field. Here is the code snippet:

def updateParameters(self):
 if self.params[0].value and self.params[1].value:
 fc = str(self.params[0].value)
 col = str(self.params[1].value)
 self.params[2].filter.list = sorted(
 set(
 row[0] for row in arcpy.da.SearchCursor(fc, [col]) if row[0]
 )
 )

By default, none of the value is checked in the tool.

Unselected values

How can I check all values of multivalue parameter through ToolValidation class using python 2.7?

All selected

Answer 1

You can set the value of the parameter to the values you want to be checked, at least when using a Python Toolbox. The same should be true for your case.

For example:

def getParameterInfo(self):
 p = arcpy.Parameter()
 p.datatype = 'String'
 p.multiValue = True
 p.name = 'test'
 p.displayName = 'Test'
 p.parameterType = 'Required'
 p.direction = 'Input'
 p.filter.list = ['One','Two','Three','Four']
 return [p]
def updateParameters(self, parameters):
 parameters[0].value = ['Two','Four'] 
 return

enter image description here

edit

For your code example this would look like:

def updateParameters(self):
 if self.params[0].value and self.params[1].value:
 fc = str(self.params[0].value)
 col = str(self.params[1].value)
 vals = sorted(set(row[0] for row in arcpy.da.SearchCursor(fc,[col]) if row))
 self.params[2].filter.list = vals
 self.params[2].value = vals

• Alex Tereshenkov: The problem here is that you don't know what strings will come forehand, so you cannot set them checked on parameter update, isn't it?
• Evil Genius: @AlexTereshenkov In some cases you may not, but in Surya's example, the values are being explicitly added in updateParameters, so of course they are known.
• Evil Genius: @AlexTereshenkov Sure. I was trying to explain how it worked rather than "paste this into your code," but I can see how it's confusing
• Hornbydd: @EvilGenius great answer but I'm curious, where in the Help does it say that sending a list to the value property checks on/off checkboxes?
• Evil Genius: @Hornbydd I couldn't find anything in the docs that relates to this, but given that the value is set to a ValueTable containing the selected items when the tool is run, it made sense to set it to a list to select the values beforehand. I tested it and it works, although possibly not documented.