Hi,
If I understand you well you have a form with dropdown and you want the value of the dropdown to filter
the query given by the eventtype. if I'm not wrong, What you have to do is:
1- create your dropdown populated by a search that gives you the appropriat values you will use to filter the eventtype
2- place the token in the query as you desire.
THE FOLLOWING IS AN EXAMPLE OF FORM LIKE THAT(i'm using splunk 6.2):
the eventtype is about source and i filter it with sources values from the dropdown.
<form>
<label>Dashb_test</label>
<fieldset submitButton="false">
<input type="dropdown" token="source">
<choice value="*">all</choice>
<search>
<query>index=* source=* |stats c by source</query>
</search>
<fieldForLabel>source</fieldForLabel>
<fieldForValue>source</fieldForValue>
</input>
</fieldset>
<row>
<panel>
<event>
<search>
<query>index=* eventtype=source_eventtype|search source=$source$</query>
<earliest></earliest>
<latest></latest>
</search>
</event>
</panel>
</row>
</form>