IsAssignableFrom not working

[SamuelJohnsonMedia]

Description

Following the steps to create a plugin architecture as shown in the MS Docs and is failing to compare the implemented interface from the loaded assembly using:

foreach( var type in assembly.GetTypes() )
{
  var found = typeof( ICommand ).IsAssignableFrom( type );
  // found should be true but is not!
}

Whereas this works (as you would expect):

var found = typeof( ICommand ).IsAssignableFrom( typeof( HelloCommand ) )

So does this:

var myFilter = new TypeFilter( (c, o) => c.ToString() == o.ToString() );
var interfaces = type.FindInterfaces( myFilter, typeof( ICommand ) );
if( interfaces.Length > 0 )
{
  // found
}

Please see attached solution for example:
PluginsTest.zip

Configuration

Dotnet: .net 5.0.100-rc.2.20479.15
OS: Windows 10 Pro
Configuration: Any CPU (running on x64 laptop)

Regression?

This doesn't seem to work with .netcore3.1 or 3.0 either in either Visual Studio 2019 or 2019 Preview 6

[Dotnet-GitSync-Bot]

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[am11]

The issue is that ICommand is loaded as different type. See dotnet/docs#15811.
In your attached project, apply this patch to get the expected result:

--- a/HelloPlugin/HelloPlugin.csproj
+++ b/HelloPlugin/HelloPlugin.csproj

  <ItemGroup>
-    <ProjectReference Include="..\PluginBase\PluginBase.csproj" />
+    <ProjectReference Include="..\PluginBase\PluginBase.csproj" Private="false" ExcludeAssets="runtime" />
  </ItemGroup>

[ghost]

Tagging subscribers to this area: @vitek-karas, @agocke
See info in area-owners.md if you want to be subscribed.

[SamuelJohnsonMedia]

@am11 that does not work for me no matter what I try I have tried your suggestion but also the docs suggestion:

  <ItemGroup>
    <ProjectReference Include="..\PluginBase\PluginBase.csproj">
      <Private>false</Private>
      <ExcludeAssets>runtime</ExcludeAssets>
    </ProjectReference>
  </ItemGroup>

[am11]

It needs clean folder: delete all bin and obj directories (or extract the zip attachment in new place, apply the patch and build+run).

[SamuelJohnsonMedia]

Yes I have done all that multiple times; I have manually deleted all the bin/obj folders

[am11]

My steps on Windows 10 are:

• Download .NET 5 RTM zip file for Windows from https://github.com/dotnet/installer#installers-and-binaries, and extract at C:\Temp\dotnet5\.
• Download your zip file and apply the aforementioned patch, along with:

  --- Program.cs
  +++Program.cs
          // Load commands from plugins.
          string[] pluginPaths = new string[]
          {
  -            "C:/Projects/Tests/PluginsTest/HelloPlugin/bin/Debug/net5.0/HelloPlugin.dll"
  +           "PluginsTest/HelloPlugin/bin/Debug/net5.0/HelloPlugin.dll"
          };

• Execute these in sequence:

  # PowerShell
  $ \temp\dotnet5\dotnet build
  $ \temp\dotnet5\dotnet run PluginsTest.csproj

outputs:

Loading commands from: C:\Temp\PluginsTest\HelloPlugin\bin\Debug\net5.0\HelloPlugin.dll
-- .\PluginsTest.csproj --
No such command is known.

which is different than what it produces without the HelloPlugin.csproj patch:

Loading commands from: C:\Temp\PluginsTest\HelloPlugin\bin\Debug\net5.0\HelloPlugin.dll
System.ApplicationException: Can't find any type which implements ICommand in HelloPlugin, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null from C:\Temp\PluginsTest\HelloPlugin\bin\Debug\net5.0\HelloPlugin.dll.
Available types: HelloPlugin.HelloCommand
   at PluginsTest.Program.CreateCommands(Assembly assembly)+MoveNext() in C:\Temp\PluginsTest\Program.cs:line 107
   at System.Collections.Generic.List`1.InsertRange(Int32 index, IEnumerable`1 collection)
   at System.Collections.Generic.List`1.AddRange(IEnumerable`1 collection)
   at System.Linq.Enumerable.SelectManySingleSelectorIterator`2.ToList()
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at PluginsTest.Program.Main(String[] args) in C:\Temp\PluginsTest\Program.cs:line 29

[SamuelJohnsonMedia]

That looks like it hasnt worked; it should have output the commands available in the PlugIn and not No such command is known

[am11]

So we can't blame IsAssignableFrom API for this?

      foreach( Type type in assembly.GetTypes() )
      {
        if( typeof( ICommand ).IsAssignableFrom( type ) )
        {
          var result = Activator.CreateInstance( type ) as ICommand;
          if( result != null )
          {
            count++;
            yield return result;
          }
        }
      }

      if( count == 0 )
      {
        string availableTypes = string.Join( ",", assembly.GetTypes().Select( t => t.FullName ) );
        throw new ApplicationException(
            $"Can't find any type which implements ICommand in {assembly} from {assembly.Location}.\n" +
            $"Available types: {availableTypes}" );
      }

IsAssignableFrom seems to be working as expected.

[SamuelJohnsonMedia]

I delete the whole project and re-downloaded, applied your patch and then ran it through VS 2019 Preview and it worked:

Loading commands from: C:\Projects\Tests\PluginsTest\HelloPlugin\bin\Debug\net5.0\HelloPlugin.dll
Commands:
hello    - Displays hello message.

Feels a bit flakey, but thanks ... now to try and get this working in my actual project

[am11]

The code is written in a way that it looks for command in first argument, we need to publish it first, as opposed to running with dotnet-run (which passes first argument as project path):

$ \temp\dotnet5\dotnet publish
$ \temp\dotnet5\dotnet bin\Debug\net5.0\PluginsTest.dll hello
Loading commands from: C:\Temp\PluginsTest\HelloPlugin\bin\Debug\net5.0\HelloPlugin.dll
-- hello --
Hello !!!

[vitek-karas]

dotnet run doesn't take the project as a parameter on its own, instead it's an option, so dotnet run Project.csproj will treat Project.csproj as the first command line parameter for the app. If you want to specify the project to run that's done via dotnet -p Project.csproj in which case there will be no command line parameters passed to app. And so dotnet run -p Project.csproj hello will pass hello as the only command line parameter to the app.

[SamuelJohnsonMedia]

I think this can be closed now; thanks for everyones input and help.