Can I make the default AppDomain use shadow copies of certain assemblies?

Question

A short explanation of why I want to do this:

I am busy writing a plugin for Autodesk Revit Architecture 2010. Testing my plugin code is extremly cumbersome, as I have to restart Autodesk for each debug session, manually load a Revit project, click on the Add-Ins tab and then start my plugin. This is just taking too long.

I have written a second plugin that hosts an IronPython interpreter. This way, I can play around with the API provided by Revit. But eventually, the code has to be rewritten in C# - and debugged.

Easy, I thought: Just load the plugins DLL from the IronPython script and exercise it. This does work, but once loaded, I cannot recompile in Visual Studio, as the DLL is now loaded in Revits AppDomain.

Easy, I thought (with a little help from StackOverflow): Just load the DLL in a new AppDomain. Alas, the RevitAPI objects can't be marshaled to another AppDomain, as they don't extend MarshalByRefObject.

I think I might be onto something with shadow copies. ASP.NET seems to be doing this. But reading the documentation on MSDN, it seems I can only specify this when creating an AppDomain.

Can I change this for the current (default) AppDomain? Can I force it to use shadow copies of DLLs from a specific directory?

Answer 1

I don't know what you are trying to do but there are some deprecated methods to turn on ShadowCopy on the current AppDomain.

AppDomain.CurrentDomain.SetCachePath(@"C:\Cache");
AppDomain.CurrentDomain.SetShadowCopyPath(AppDomain.CurrentDomain.BaseDirectory);
AppDomain.CurrentDomain.SetShadowCopyFiles();

Answer 2

Sometimes it's not possible to modify the Main() method code because, for example, you're writing a plug-in and it's instantiated by a manager.

In that case i suggest you copy the assembly and pdb (and dependent ones in AssemblyResolve event) to a temp location and load them from there with Assembly.LoadFile() (not LoadFrom()).

Pros: - no dll locking. - every time the target assembly is recompiled you get access to the new version (that's why .LoadFile()). - the whole assembly is fully available in AppDomain.CurrentDomain.

Cons: - file copying is necessary. - assemblys can't be unloaded and that could be inconvenient because resources are no freed.

Regards,

PD: This code does the work.

/// <summary>
/// Loads an assembly without locking the file
/// Note: the assemblys are loaded in current domain, so they are not unloaded by this class
/// </summary>
public class AssemblyLoader : IDisposable
{
    private string _assemblyLocation;
    private string _workingDirectory;
    private bool _resolveEventAssigned = false;

    /// <summary>
    /// Creates a copy in a new temp directory and loads the copied assembly and pdb (if existent) and the same for referenced ones. 
    /// Does not lock the given assembly nor pdb and always returns new assembly if recopiled.
    /// Note: uses Assembly.LoadFile()
    /// </summary>
    /// <param name="assemblyOriginalPath"></param>
    /// <returns></returns>
    public Assembly LoadFileCopy(string assemblyLocation)
    {
        lock (this)
        {
            _assemblyLocation = assemblyLocation;

            if (!_resolveEventAssigned)
            {
                _resolveEventAssigned = true;

                AppDomain.CurrentDomain.AssemblyResolve += new ResolveEventHandler(AssemblyFileCopyResolveEvent);
            }

            //  Create new temp directory
            _workingDirectory = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());
            Directory.CreateDirectory(_workingDirectory);

            //  Generate copy
            string assemblyCopyPath = Path.Combine(_workingDirectory, Path.GetFileName(_assemblyLocation));
            System.IO.File.Copy(_assemblyLocation, assemblyCopyPath, true);

            //  Generate copy of referenced assembly debug info (if existent)
            string assemblyPdbPath = _assemblyLocation.Replace(".dll", ".pdb");
            if (File.Exists(assemblyPdbPath))
            {
                string assemblyPdbCopyPath = Path.Combine(_workingDirectory, Path.GetFileName(assemblyPdbPath));
                System.IO.File.Copy(assemblyPdbPath, assemblyPdbCopyPath, true);
            }

            //  Use LoadFile and not LoadFrom. LoadFile allows to load multiple copies of the same assembly
            return Assembly.LoadFile(assemblyCopyPath);
        }
    }

    /// <summary>
    /// Creates a new copy of the assembly to resolve and loads it
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="args"></param>
    /// <returns></returns>
    private Assembly AssemblyFileCopyResolveEvent(object sender, ResolveEventArgs args)
    {
        string referencedAssemblyFileNameWithoutExtension = System.IO.Path.GetFileName(args.Name.Split(',')[0]);

        //  Generate copy of referenced assembly
        string referencedAssemblyPath = Path.Combine(Path.GetDirectoryName(_assemblyLocation), referencedAssemblyFileNameWithoutExtension + ".dll");
        string referencedAssemblyCopyPath = Path.Combine(Path.GetDirectoryName(args.RequestingAssembly.Location), referencedAssemblyFileNameWithoutExtension + ".dll");
        System.IO.File.Copy(referencedAssemblyPath, referencedAssemblyCopyPath, true);

        //  Generate copy of referenced assembly debug info (if existent)
        string referencedAssemblyPdbPath = Path.Combine(Path.GetDirectoryName(_assemblyLocation), referencedAssemblyFileNameWithoutExtension + ".pdb");
        if (File.Exists(referencedAssemblyPdbPath))
        {
            string referencedAssemblyPdbCopyPath = Path.Combine(Path.GetDirectoryName(args.RequestingAssembly.Location), referencedAssemblyFileNameWithoutExtension + ".pdb");
            System.IO.File.Copy(referencedAssemblyPath, referencedAssemblyCopyPath, true);
        }

        //  Use LoadFile and not LoadFrom. LoadFile allows to load multiple copies of the same assembly
        return Assembly.LoadFile(referencedAssemblyCopyPath);
    }


    public void Dispose()
    {
        Dispose(true);
    }

    private void Dispose(bool disposing)
    {
        if (disposing)
        {
            if (_resolveEventAssigned)
            {
                AppDomain.CurrentDomain.AssemblyResolve -= new ResolveEventHandler(AssemblyFileCopyResolveEvent);

                _resolveEventAssigned = false;
            }
        }
    }
}

Answer 3

There is now a Revit plugin for dynamically loading/unloading other Revit plugins so that you can change, recompile, and test without having to reopen the Revit Project. I found it on the Building Coder blog. It comes with the Revit SDK.