[wix-users] Request for additional information on installing WiX Bootstrapper prerequisite before displaying the UI

[Ben Key]

Yesterday I asked a question about whether or not it is possible to have
one or more prerequisites installed before the Burn custom user interface.
The specific scenario I have in mind is that the custom user interface
depends on the prerequisites. Unfortunately, the responses I received were
excessively vague.


However, I believe I finally have enough information to be able to give a
definite answer to the question of whether or not it is possible to use
Burn to install a prerequisite before the Custom UI is displayed. The
responses did contain all the necessary pieces of the puzzle. I just needed
to do more research and pondering in order to put the puzzle together.


First, I will give some information on the pieces of the puzzle that helped
me to figure this out.


One response to my question here on the WiX-Users group included an
extremely vague reference to “mba (the managed bootstrapper application
host and friends)” with no links to help me to interpret this. A Google
search for “WiX managed bootstrapper application” yielded thousands of
results. Most of them did not reference the concept of prerequisites at all
and thus did not help much. However, I eventually did find the article
Introducing
Managed Bootstrapper Applications
<http://blogs.msdn.com/b/heaths/archive/2011/10/28/introducing-managed-bootstrapper-applications.aspx>,
which indirectly references the concept of prerequisites in that the
WixMbaPrereqPackageId WixVariable is used. A Google search revealed that
this variable is used to define the package group that the managed
bootstrapper application depends on.


Another response to my question here on the WiX-Users group suggested that
I “look at ExePackage/@PrereqSupportPackage for adding multiple packages to
the prereq installer prior to loading the mba.” Again, no links were
provided to help me to interpret this response and a Google search proved
to be only a little more helpful. A search for PrereqSupportPackage led me
to the documentation for PrereqSupportPackage Attribute (Bal Extension)
<http://wixtoolset.org/documentation/manual/v3/xsd/bal/prereqsupportpackage.html>
which contains the following extremely unhelpful information.

When set to "yes", the Prereq BA will plan the package to be installed if
its InstallCondition is "true" or empty.

That description is entirely unhelpful since it does not describe its
purpose. The only clue is that it contains the magical word prereq.


Another result in my Google search for PrereqSupportPackage was an earlier
question here on the WiX-Users mailing list titled Installing .Net 4.0.3
Prerequisites required for managed bootstrapper
<http://wix-users.narkive.com/qicV1CkE/installing-net-4-0-3-prerequisites-required-for-managed-bootstrapper>.
There is a single response to this question that suggests that the
PrereqSupportPackage attribute can be used “to indicate that more than one
package is required” as a prerequisite. This suggested that the answer to
the prerequisite question just might be the PrereqSupportPackage attribute.
However, the response also contains the following rather disappointing
information, which suggests that this might not be the solution. “A problem
you might have is that pre-req packages are only installed if your BA fails
to start.”


The idea that the PrereqSupportPackage attribute might not be the solution
was reinforced by another question here on the WiX-Users mailing list
titled PrereqSupportPackage only for .Net Prerequisites
<http://windows-installer-xml-wix-toolset.687559.n2.nabble.com/PrereqSupportPackage-only-for-Net-Prerequisites-td7597503.html>.
The response to this question was “PrereqSupportPackage was pretty much
designed for .NET prerequisites.”

Other responses I received here on the WiX-Users group essentially stated
it is your BA and you are in control. This would have been more helpful if
even one sentence was included to suggest how to accomplish this control.


The single response I received to my question on Stack Overflow was just a
little more helpful. It contained the following paragraph.

After this you can do the various installation phases such as Detect, Plan
and Apply. Showing your UI is simply using the .Show() method on a wpf page
for example. Therefore you could delay showing the user your Ui till
whenever you want in the installation.

I obtained the final piece of the puzzle by examining the source code for
WiX to obtain more information on the PrereqSupportPackage attribute since
this is the most promising lead I have thus far. Support for the
PrereqSupportPackage attribute is found in the wixstdba project,
specifically in the file
*ext\BalExtension\wixstdba\WixStandardBootstrapperApplication.cpp*. The
wixstdba project contains code that adds all packages with the
PrereqSupportPackage attribute to a prerequisite package dictionary. The
installers in the prerequisite package dictionary are installed if the
m_fPrereq member variable is true. All other packages are installed if the
m_fPrereq member variable is false. The m_fPrereq member variable is
initialized using the value passed to the fPrereq parameter of the
CreateBootstrapperApplication function.


This led me to investigate calls to the CreateBootstrapperApplication
function. The wixstdba project provides two exported functions for creating
the bootstrapper application, BootstrapperApplicationCreate and
MbaPrereqBootstrapperApplicationCreate. The BootstrapperApplicationCreate
function calls the CreateBootstrapperApplication function with the fPrereq
parameter set to false and the MbaPrereqBootstrapperApplicationCreate
function calls the CreateBootstrapperApplication function with the fPrereq
parameter set to true.


The next step was of course to find out when the functions
MbaPrereqBootstrapperApplicationCreate and BootstrapperApplicationCreate
are called. I found the answer in ext\BalExtension\mba\host \host.cpp. The
MbaPrereqBootstrapperApplicationCreate function is only called if the
GetAppDomain function fails. Thus when using the
WixStandardBootstrapperApplication the statement that “pre-req packages are
only installed if your BA fails to start” appears to be true.


However, when using a custom Managed Bootstrapper Application the wixstdba
project is not used. Just because the wixstdba project only processes
packages with the PrereqSupportPackage attribute set when called from the
context of the MbaPrereqBootstrapperApplicationCreate function does not
mean that a custom Managed Bootstrapper Application must do the same.


This is when the final solution occurred to me. Our custom Managed
Bootstrapper Application could support the PrereqSupportPackage attribute.
All packages with this attribute set could be installed before the UI is
displayed. All packages without the attribute set could be installed after
the UI is displayed by the Show function.


Is this overall analysis correct? Does anyone have any suggestions to add?


Thanks. I am asking for additional information both so that I will be able
to complete a task my employer has assigned me and in the hopes that others
who encounter this issue will not have as much difficulty obtaining this
information as I have.