Currently Nvn Installer supports only win32 DLL. If you are unfamiliar with C and/or C++ then creating a properly functioning DLL custom action is not a minor effort. Jscript and/or VBScript custom actions have a much lower learning curve. Refer Jscript Help or VBScript Help to know how to create simple custom action.
[Image: with one DLL custom action. without any other custom action]

Custom Action Name - This can be any text description for your reference.

File Path - Path of custom action DLL.
This depends on the value of "Is part of installation". Select appropriate value before you select file path.

Is part of installation -
If value is true, then custom action DLL is considered as one of the file to be installed on target machine. When you try to select file path i.e. when you click "...", pop up is shown with all files and folders.  Select the DLL file which handles this custom action. Nvn Installer does not make any validation to check whether selected file can really handle the respective custom action.

Following dialog shown with all components when “IS part of installation” is true.
[Image: with components form shown]

If value is false (default value) - It is considered as binary file which is executed during installation and the file is not stored anywhere on the target system. Microsoft installer cleans it after completing the installation or rollback on installation failure.

Normal file select dialog is shown when “IS part of installation” is false.

[Image: select file dialog]

DLL Entry is the function to be called

when? – Following are the three available options.
1. Installation - This custom action is executed only during installation. For example a custom action creates a directory in C: \<directory>. If option selected is installation, then directory is created only during installation, but not during uninstallation or when installation fails.
2. Uninstallation - This is executed only during uninstallation.
3. Rollback - Windows installer will clean up everything if installation fails, like all directories, registries etc. But it cannot rollback anything done by the custom actions. So create rollback custom action to restore target machine in case of any installation failure.
It is recommended to create uninstallation and rollback custom action for every custom action that runs during installation.

It is also recommended to place uninstallation or rollback custom action next to the corresponding installation custom action. But the order between uninstallation and rollback custom actions does not really matter.

Download sample - Read Steps.txt in the sample to know how to create a simplest custom action DLL and using the same with Nvn Installer.

For any questions, suggestions or bug reports, please drop a mail to support@nvninstaller.com