Process model hit by dropdown value

Hi, no we can not EDIT: synchronously start a process on dropdown selection.  

Check this link  Ways to start a process model in Appian

As Stewart mentions, you can certainly start a process asynchronously via the dropdown's saveInto, such as:

a!localVariables(
  local!options: {"Red","Blue","Green"},
  local!selection,
  local!processStarted,
  
  a!dropdownField(
    label: "Dropdown",
    placeholder: "-- Select --",
    choiceLabels: local!options,
    choiceValues: local!options,
    value: local!selection,
    saveInto: {
      local!selection,
      if(
        local!selection="Green",
        a!startProcess(
          processModel: cons!YOUR_PM_HERE,
          onSuccess: a!save(local!processStarted,true),
          onError: a!save(local!processStarted,false)
        ),
        {}
      )
    }
  )
)

I worry that the previous replies here are, perhaps, "putting the cart before the horse", i.e. reading details into the request that it might not necessarily be asking.

Can you clarify a bit what exactly you intend by "hit process model through dropdown value"?  For example, if you want a user to be able to select a dropdown in one interface, then submit the form, then subsequently in that process flow, choose a subprocess depending on what value was chosen, that's fairly easy, and basically considered as "classic functionality" - you'd just have an XOR gateway choosing the process flow to execute based on what value had been provided by the user.

If you mean something else, something more complicated or something more reliant on newer functionality, then you'll need to provide considerably more detail behind what you're thinking of trying to accomplish, than a single phrase.