Is is possible to pass a variable from the build process to Visual Basic code? - vb.net

Question

My goal is to create build definitions within Visual Studio Team Services for both test and production environments. I need to update 2 variables in my code which determine which database and which blob storage the environment uses. Up till now, I've juggled this value in a Resource variable, and pulled that value in code from My.Resources.DB for a library, and Microsoft.Azure.CloudConfigurationManager.GetSetting("DatabaseConnectionString") for an Azure worker role. However, changing 4 variables every time I do a release is getting tiring.
I see a lot of posts that get close to what I want, but they're geared towards C#. For reasons beyond my influence, this project is written in VB.NET. It seems I have 2 options. First, I could call the MSBuild process with a couple of defined properties, passing them to the .metaproj build file, but I don't know how to get them to be used in VB code. That's preferable, but, at this point, I'm starting to doubt that this is possible.
I've been able to set some pre-processor constants, to be recognized in #If-#Else directives.
#If DEBUG = True Then
BarStaticItemVersion.Caption = String.Format("Version: {0}", "1.18.0.xxx")
#Else
BarStaticItemVersion.Caption = String.Format("Version: {0}", "1.18.0.133")
#End If
msbuild CalbertNG.sln.metaproj /t:Rebuild /p:DefineConstants="DEBUG=False"
This seems to work, though I need to Rebuild to change the value of that constant. Should I have to? Should Build be enough? Is this normal, or an indication that I don't have something set quite right?
I've seen other posts that talk about pre-processing the source files with some other builder, like Ant, but that seems like overkill. It feels like I'm close here. But I want to zoom out and ask, from a clean sheet of paper, if you're given 2 variables which need to change per environment, you're using VB.NET, and you want to incorporate those variable values in an automated VS Team Services build process upon code check-in, what's the best way to do it? (I want to define the variables in the VSTS panel, but this just passes them to my builder, so I have to know how to parse the call to MSBuild to make these useful.)
I can control picking between 2 static strings, now, via compiler directives, but I'd really like to reference the Build.BuildNumber that comes out of the MSBuild process to display to the user, and, if I can do that, I can just feed the variables for database and blob container via the same mechanism, and skip the pre-processor.

Answer 1

You've already found the way you can pass data from the MsBuild Arguments directly into the code. An alternative is to use the Condition Attribute in your project files to make certain property groups optional, it allows you to even include specific files conditionally. You can control conditions by passing in /p:ConditionalProperty=value on the MsBuild command. This at least ensures people use a set of values that make sense together.
The problem is that when MsBuild is running in Incremental mode it is likely to not process your changes (as you've noticed), the reason for this, is that the input files remain unchanged since the last build and are all older than the last generated output files.
To by-pass this behavior you'd normally create a separate solution configuration and override the output location for all projects to be unique for that configuration. Combined with setting the Compiler constants for that specific configuration you're ensured that when building that Configuration/Platform combination, incremental builds work as intended.
I do want to echo some of the comments from JerryM and Daniel Mann. Some items are better stored in else where or updated before you actually start the compile phase.
Possible solutions:
Store your configuration data in config files and use Configuration Transformation to generate the right config file base don the selected solution configuration. The process is explained on MSDN. To enable configuration transformation on all project types, you can use SlowCheetah.
Store your ocnfiguration data in the config files and use MsDeploy and specify a Parameters.xml file that matches the deploy package. It will perform the transformation on deploy time and will actually allow your solution to contain a standard config file you use at runtime, plus a publish profile which will post-process your configuration. You can use a SetParameters.xml file to override the variables at deploy time.
Create an installer project (such as through Wix) and merge the final configuration at install time (similar to the MsDeploy). You could even provide a UI which prompts for specific values (and can supply default values).
Use a CI server, like the new TFS/VSTS 2015 task based build engine and combine it with a task that can search&replace tokens, like the Replace Tokens task, Tokenization Task, Colin's ALM Corner Build and Release Tasks. And a whole bunch that specifically deal with versioning. Handling these things in the CI server also allows you to do a quick build locally at all times and do these relatively expensive steps on the build server (patching source code breaks incremental build in MsBuild, because there are always newer input files.
When talking specifically about versioning, there are a number of ways to set the AssemblyVersion and AssemblyFileVersion just before compile time, usually it involves overriding the AssemblyInfo.cs file before compilation. Your code could then use reflection to read the value at runtime. You can use the AssemblyInformationalversion to specify something like you do in the example above which contains .xxx or other text. It also ensures that the version displayed always reflects the information obtained when reading the file properties through Windows Explorer.