How do I direct the installer to perform actions before showing a page?

You can direct the installer to perform actions before a page is shown by using a <preShowPageActionList> section. The following example presents the user with information that stored in a registry key under Windows and in an environment variable under Linux.

<infoParameter>
  <preShowPageActionList>
    <registryGet>
   <variable>some_info</variable>
       <key>HKEY_LOCAL_MACHINE\SOFTWARE</key>
      <name>MYAPP</name>
      <ruleList>
        <compareText>
         <text>${platform_name}</text>
         <logic>equals</logic>
         <value>windows</value>
        </compareText>
      </ruleList>
   </registryGet>
   <setInstallerVariable>
     <name>some_info</name>
     <value>${env(SOMEINFO)}</value>
     <ruleList>
        <compareText>
         <text>${platform_name}</text>
         <logic>equals</logic>
         <value>linux</value>
        </compareText>
     </ruleList>
    </setInstallerVariable>
  </preShowPageActionList>
  <name>display_info</name>
  <title>License File Information</title>
  <explanation>This screen shows important information about licensing issues</explanation>
  <value>Important Information! Setup has detected the following : ${some_info}.
In the following screen you will be asked to confirm the information or enter a new (...)</value>
</infoParameter>