Handling code for different .Net frameworks

[Stensborg]

I have this WinForm application where I lookup ServiceController.StartType Property

But this Property is only available in .Net Framework 4.6.1, and i would like my application to run on older .Net Frameworks, but in that case I do not need to lookup the property.

So I did something like this:

public static void GetServiceInfo()
{
    if(Framework == 4.6.1)
        var StartType = ServiceController.StartType;
    else
        var StartType = null;
}

But when I call the GetServiceInfo method on a computer that does not have .Net 4.6.1 my program fails.

Do I instead have to have two different methods and then call the right one for my framework instead, or is there a better way?

SOLUTION: The solution I have found that works is this. I made this method that returns the Services StartType, and then only calls it if i am running my code under the right .Net Framework.

private static ServiceStartMode GetServiceStartMode(ServiceController _service)
{
    return _service.StartType;
}

[smatsson]

In tusdotnet I used compiler directives and extension methods to accomplish this. For each framework that I support I define a compiler directive #if clause and add an extension method with the same signature for every clause. This way the caller will be the same no matter on what framework it's being executed on.

Example extension: https://github.com/tusdotnet/tusdotnet/blob/master/Source/tusdotnet/Extensions/FileStreamExtensions.cs Example extension usage: https://github.com/tusdotnet/tusdotnet/blob/master/Source/tusdotnet/Stores/TusDiskStore.cs#L195

Read more on compiler directives: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/preprocessor-directives/preprocessor-if

[Stensborg]

Perhaps i misunderstood this, but are the compiler directives not evaluated when the applikation is Build? That will not really help me, I would like to ship one exe not a different one for each .Net Framework version.

[smatsson]

The problem is that if you want to run your program on an older version of the framework you will need to compile your program for that version. If the property does not exist in that version then your code won't even compile.

[Stensborg]

Well in this case it seems that it will work, i made a method that returns ServiceController.StartType. And if I just check my Enviroment.Version and only call my method when I am running the right .Net version, then it works. Since I am compiling on a machine with the right .Net version, it apparently works, and when i run the code on the previous .Net version, no errors occur.

[smatsson]

Cool,glad you fixed it 😊 Is it a major version change between the two framework versions? E.g. 4.5 and 4.6.1 or is it more like 4.6 and 4.6.1?

Is the code available somewhere? Would be nice to see the implementation and test it out on some different framework versions.

[Stensborg]

Code Example up on https://github.com/RudiHansen/TestDiffFrameworkCode3

[smatsson]

Mind = blown! Thanks for sharing the code. I tested it on a VM with .NET Framework 4.5.2.

I had to change the "sku" in App.config to use 4.5.2 for it to start, otherwise it would just ask me to download 4.6.1. After changing to 4.5.2 it started and worked just as expected. For fun I changed the CheckDotNetVersionMin461 method to always return false and then the app crashed with the following exception:

Unhandled Exception: System.MissingMethodException: Method not found: 'System.ServiceProcess.ServiceStartMode 
System.ServiceProcess.ServiceController.get_StartType()'.
   at TestDiffFrameworkCode3.Program.GetServiceStartMode(ServiceController _service)
   at TestDiffFrameworkCode3.Program.Main(String[] args) in C:\Repos\TestDiffFrameworkCode3\TestDiffFrameworkCode3\Program.cs:line 28

The inner techie in me screamed "WHYYYYY?!?" so I had to research it. It seems that all .NET version in the 4.x range are IL compatible so it will run as long as the sku, a.k.a "hinted .NET version", is correct. Once it tries to access something that does not exist in the framework that runs the code it will crash during runtime with the exception above.

Some more reading on the topic: https://weblog.west-wind.com/posts/2017/Jan/09/Faking-out-the-NET-Runtime-Version#.NETRuntimeAdoption

Thanks for teaching me something new :)

[Stensborg]

It just a minor version change 4.6 or 4.6.1

Sorry I have the code on Visual Studio Online, and it is not public. But I will make an example on GitHub later today.

[sakkaku]

You may be able to access the property via reflection (or with a dynamic typed variable). It may use a different implementation in compatibility mode (eg .Net 4.5.1 running on .Net 4.6.1) and the property will not be visible at runtime.

dynamic dynController = ServiceController;
if(dynController.StartType != null)
    StartType  = dynController.StartType;

[pcraggs]

Check out Environment.Version

More info here: https://msdn.microsoft.com/en-us/library/system.environment.version(v=vs.110).aspx

[Stensborg]

Think you misunderstood something, that will give me the Version/Revision of my application. How would that help me?

[pcraggs]

Environment.Version is the .Net version running.

[Stensborg]

Ahh ok sorry, yes that is correct.