Prerequisite Handler
A prerequisite handler is a specialised action sequence that performs pre-installation actions to install a prerequisite for the installation or your product. Prerequisite handlers differ from regular action sequences in the following respects:
- They are executed by the standard action InstallPrerequisites that has special knowledge of prerequisite handling.
- Prerequisite handlers have a Condition field and a Platforms option, and are only executed if the condition evaluates to True and the current installation platform is among the handler's selected platforms.
- Prerequisite handlers may be marked to require Administrator rights and another standard action, CheckPrerequisites, will check if these rights are available prior to executing the handler.
- Prerequisite handlers should be used for custom actions (downloading and installing special system components, for example) and not for regular installation actions.
When you create a new InstallMate project, it contains prerequisite handlers for commonly used prerequisites. To use those for your own installer, simply select them in the tree on the Prerequisites project page. We do not recommend that you modify them unless you have a thorough understanding of their operation.
Attributes
The following attributes and options are available.
| Attribute | Description |
|---|---|
| Name | The internal name of the prerequisite handler. This name is only used in InstallMate and is not visible to the user. You must use this name if you want to refer to the prerequisite handler, for example in the Dependencies field of other handlers. |
| Description | The description of the prerequisite handler as it appears in the tree and list on the Prerequisites project page. This is for your convenience only; the description is not used by the installer. |
| Dependencies | Enter a comma-separated list of prerequisite handlers on which the current one depends. The dependencies will be evaluated and, if necessary, installed before the current handler is executed. Tip: You do not need to select the dependencies manually in the tree on the Prerequisites project page; all required dependencies will be automatically included in the installer. |
| Administrator rights required | Check this box if the prerequisite handler requires Administrator rights for one or more of its actions. This is typically the case if the handler installs a system component. If this box is checked, then the CheckPrerequisites standard action will check if these rights are available prior to executing the handler and prevent installation if not. |
| Condition | Enter the conditional expression that determines if the prerequisite handler will be executed, or leave empty for unconditional execution. Typically, this field contains a conditional expression that tests if the prerequisite is missing from the target system and returns True if so (thus executing the handler to install the prerequisite). |
| Platforms | Click this button to open the Select Installation Platforms dialog box that allows you to select the Windows versions on which the prerequisite handler must be executed. This platform selection acts as an additional condition for the handler. |
| Comment | Enter a short description of the action sequence's purpose. This is for your own documentation only; the installer does not use this field. |