WiX installer - Set ApplicationFolder from ComboBox - wix

Question

I'm writing a WiX installer for a group of medical device SW products that must install in specific directories off the root of C:. IE no "ProgramFolders" for these.
They run in dedicated environments and have been verified and validated using these directories.
I have a custom welcome dialog that has a combobox:
<Control Id="TypeCombo" Type="ComboBox" X="178" Y="162" Width="120" Height="20" Property="InstallChoiceResult" ComboList="yes" Sorted="no">
<ComboBox Property="InstallChoiceResult">
<ListItem Text="Base dev 1" Value="1"/>
<ListItem Text="Base dev 2" Value="2"/>
<ListItem Text="Base dev 3" Value="3"/>
<ListItem Text="Base Simulator" Value="4"/>
</ComboBox>
</Control>
The choice by the FSE sets the property "InstallChoiceResult". After they hit next I need to set my application folder based on their choice. IE if they chose "Base dev 1" then I need to set APPLICATIONFOLDER to C:\BASEDEV1. If they choose Base dev 2 then we go to C:\BASEDEV2
Being new to WiX I'm strugging with the sequence. It seems from examining my MSI with Orca that the InstallUISequence comes AFTER the costing occurs. When I try to set the APPLICATION folder using a group of custom actions it complains that since it is a directory it must be set before CostFinalize.
I'm sure I'm missing something simple but if my UI seems to be running AFTER that how can I set the directory I need? My custom actions currently look like:
<CustomAction Id="SetDev1" Property="APPLICATIONFOLDER" Value="C:\BaseDev1" Execute="immediate" />
<CustomAction Id="SetDev2" Property="APPLICATIONFOLDER" Value="C:\BaseDev2" Execute="immediate" />
<CustomAction Id="SetDev3" Property="APPLICATIONFOLDER" Value="C:\BaseDev3" Execute="immediate" />
<CustomAction Id="SetDevS" Property="APPLICATIONFOLDER" Value="C:\BaseDevS" Execute="immediate" />
<InstallUISequence>
<Custom Action="SetDev1" Before="InstallDlg2">InstallChoiceResult=1</Custom>
<Custom Action="SetDev2" Before="InstallDlg2">InstallChoiceResult=2</Custom>
<Custom Action="SetDev3" Before="InstallDlg2">InstallChoiceResult=3</Custom>
<Custom Action="SetDevS" Before="InstallDlg2">InstallChoiceResult=4</Custom>
</InstallUISequence>
The general jest of what I need to do is basically this:
Display dialog (FSE chooses 1, 2, 3 or simulator)
After next is pressed, Set ApplicationFolder based on property from ComboBox
Install into the set ApplicationFolder
Any help would be very much appreciated.

Answer 1

You can set the directory values to APPLICATIONFOLDER using SetDirectory element. No need to use Custom action and bind the directory values directly to the List item. Make the Combo box property is public (All letter in uppercase).
<Control Id="TypeCombo" Type="ComboBox" X="142" Y="158" Width="120" Height="16" Property="INSTALLCHOICERESULT" ComboList="yes" Sorted="no">
<ComboBox Property="INSTALLCHOICERESULT">
<ListItem Text="Base dev 1" Value="C:\BaseDev1" />
<ListItem Text="Base dev 2" Value="C:\BaseDev2" />
<ListItem Text="Base dev 3" Value="C:\BaseDev3" />
<ListItem Text="Base Simulator" Value="C:\BaseDevS" />
</ComboBox>
</Control>
<SetDirectory Id="APPLICATIONFOLDER" Value="[INSTALLCHOICERESULT]" Sequence="execute" />