Hi all,

The other day I was trying to add a simple autoupdate functionality to a little tool I developed, and I needed to check the version of current assembly against the udpated one. If current assembly was older than the updated one, I needed to substitute the older one with the newer. Plain and simple.

This was my first attempt to achieve this (code has been simplified):

using System.Reflection;

using System.IO;

...
// Get current and updated assemblies

Assembly currentAssembly = Assembly.LoadFile(currentAssemblyPath);

Assembly updatedAssembly = Assembly.LoadFile(updatedAssemblyPath);
AssemblyName currentAssemblyName = currentAssembly.GetName();

AssemblyName updatedAssemblyName = updatedAssembly.GetName();
// Compare both versions

if (updatedAssemblyName.Version.CompareTo(currentAssemblyName.Version) <= 0)

{

    // There's nothing to update

    return;

}
// Update older version

File.Copy(updatedAssemblyPath, currentAssemblyPath, true);

But File.Copyfailes because current assembly is in use. Why? Because of Assembly.LoadFile. When we load an assembly no other process (including ours) can change or delete the file because we are using it. The issue is that we can't unload an assembly that we loaded in an AppDomain unless the AppDomain itself gets unloaded. Here I'm using the default AppDomain which will only get unloaded when the application exits. So then I tried creating a new AppDomain, load the assemblies in there and unload the AppDomain afterwards before changing the file. It didn't help either. So...

How can we get the assembly version without loading the assembly? The solution is easy:

using System.Reflection;

using System.IO;

...
// Get current and updated assemblies

AssemblyName currentAssemblyName = AssemblyName.GetAssemblyName(currentAssemblyPath);

AssemblyName updatedAssemblyName = AssemblyName.GetAssemblyName(updatedAssemblyPath);
// Compare both versions

if (updatedAssemblyName.Version.CompareTo(currentAssemblyName.Version) <= 0)

{

    // There's nothing to update

    return;

}
// Update older version

File.Copy(updatedAssemblyPath, currentAssemblyPath, true);

AssemblyName.GetAssemblyNamewon't load the assembly, so we can change the file afterwards.

I hope this helps.

Kind regards,

Alex (Alejandro Campos Magencio)

PS: In case you are interested, I will post my simple autoupdate code one of these days, once I have time to change a couple of things on it.