Selecting Multiple Layers with ArcPy?

Question

I have scripted tools in ArcPy that gather inputs using "GetParameterAsText", which then show up in the tool GUI like this:

But that is for gathering a single file by navigating to it and selecting it.

I want to script a tool that allows the user to drag multiple layers from the Table of Contents, just like the "Batch Project" tool below.

What is the proper scripting syntax to generate the same input field as "Input Feature Class or Dataset", and also the large field below it where the multiple layers are displayed? I am using Arc version 10.2.

Answer 1

When you go to create your script in ArcMap or Catalog, you'll want to go into the properties dialog and set your input field (of any type you need) to allow Multi Values, as circled in red here:

This allows the user to input either a single layer, file, or whatever the field dictates, or input as many as they need. In the actual arcpy script/code, the standard handling for working with these inputs is as follows:

import arcpy
import ConversionUtils #should be pathed correctly with ArcGIS/arcpy installation

inputs = ConversionUtils.gp.GetParameterAsText(0)
inputs = ConversionUtils.SplitMultiInputs(inputs)

for input in inputs:
    arcpy.Project_management(...)
    #Perform your individual actions here

Bear in mind that the ConversionUtils get parameter as text call returns all the user inputs as a string, separated by a semicolon. The second line to split them there separates them out into a standard list, which you can then iterate through or do whatever you want with.

Answer 2

Using the multivalue parameter control enables you to:

Drag and drop single or multiple layers from ArcMap onto the list.