InstallShield 2012 Spring Express Edition User Guide

Chapter 10: Customizing Installation Behavior
Using Custom Actions
Action Execution Options
Custom actions are executed in the order in which they appear in a sequence. Some actions need to be
scheduled to run immediately at the start of the installation; others need to be deferred for a later time.
The In-Script Execution setting in the Custom Actions view enables you to select which iteration of the
sequence (deferred, rollback, or commit) should trigger your action. This setting also lets you specify the
context for deferred, rollback, and commit actions: actions can run in user context (with the privileges of
the user running the installation) or in system context (with elevated privileges). If this setting is not
displayed for a particular custom action in the Custom Actions view, that action is scheduled for
immediate execution; immediate-execution custom actions always run in user context.
Immediate Execution
As its name implies, immediate-execution custom actions runs when the internal Windows Installer
installation script is being compiled. When an .msi file is launched, the Windows Installer service
converts all the tables in the installation database into an internal script. This script is built by cycling
through all the actions in the installation in the order in which they appear. The building of this script is
immediate execution. When an action that is set for immediate execution is encountered, that action is
executed. Therefore, this action launches before any file transfers are encountered, possibly even before
the end-user interface for the installation is fully loaded.
As a rule, custom actions that are scheduled for immediate execution do not modify the target system,
but only set properties and query the target system (for example, to see if the target system meets your
product’s system requirements). Custom actions that set Windows Installer properties must be
scheduled for immediate execution, and custom actions that occur in the User Interface sequence must
be scheduled for immediate execution.
Because actions of this type run before any changes have been made to the system, they cannot rely on
files that are being installed by the installation.
Deferred Execution
Deferred execution takes place when the internal script that is generated during immediate execution is
executed by the Windows Installer. After that script has been fully generated, the Windows Installer
runs the newly compiled script. The script runs through all of the actions in your sequences and executes
them in order. However, if an action is scheduled for immediate execution, the action does not run again
during deferred execution.
Actions that launch during deferred execution have access to files that are being installed as part of the
installation. As a result, you can call a custom action that calls a function from a DLL file that is installed
with your product during this phase of the installation. However, deferred execution custom actions
must take place between InstallInitialize and InstallFinalize in order to work properly.
Custom actions that rely on a file that is being installed to the target system, or that rely on other system
changes to have already been performed, must be scheduled for deferred execution.
Rollback Execution
Rollback occurs when an error is encountered by the installation or the end user cancels the installation
before it has a chance to complete. The rollback execution option allows you to set your action to execute
only during rollback. Therefore, any actions that are enabled for rollback execution are written to the
installation script, as are deferred execution actions. Unlike deferred execution actions, rollback
execution actions launch only during rollback. (Rollback custom actions run only if the installation fails
during deferred execution.)
230 ISE-1900-UG00 InstallShield 2012 Spring Express Edition User Guide