How to make input dependent on other inputs in a form?

[oriches]

How can I make a combo box dependent on another combo box in a form?

The contents of the second combo box is dependent on the selection in the first.

[iKate]

You do not necessarily have to use Advanced XML for this at least in Splunk v6.0. Here's my example of how device_type selected with radio button is passed to the search populating dropdown. In two words: just add in the beginning of populating search your previous value like device_type=$device_type$

<fieldset autoRun="true" submitButton="false">
<input type="time" searchWhenChanged="true" token="cohort"> <default>Last 30 days</default> </input>
<input type="time" searchWhenChanged="true" token="search"> <default>Last 30 days</default> </input>
<!-- Specify search when changed for the inputs -->
<input type="radio" token="device_type" searchWhenChanged="true">
  <label>Select a device type:</label>
  <default>All</default>

  <!-- Define the choices in code -->
  <choice value="*">All</choice>
  <choice value="TV">TV</choice>
  <choice value="BDP">BDP</choice>
  <choice value="WEB">WEB</choice>
  <choice value="TBL">TBL</choice>
  <choice value="MOB">MOB</choice>
</input>

<input type="dropdown" token="device_manufacturer" searchWhenChanged="true">
  <label>Select a device manfacturer:</label>
  <prefix>device_manufacturer="</prefix>
  <suffix>"</suffix>
  <default>*</default>

  <!-- Define the default value -->      
  <choice value="*">All</choice>

  <!-- Define the choices with a populating search -->
  <populatingSearch fieldForValue="device_manufacturer" fieldForLabel="device_manufacturer" earliest="-48h" latest="now">
    <![CDATA[source=sc_context_creation device_type="$device_type$" | eval device_manufacturer=lower(device_manufacturer) 
    | stats count by device_manufacturer | sort 0 - count]]>
  </populatingSearch>
</input>

[Damien_Dallimor · Accepted solution]

You'll have to use Advanced XML.

Lots of info in answers already such as this thread.