IsAssignableFrom() 在应该返回 true 时返回 false

Question

I am working on a plugin system that loads .dll's contained in a specified folder. I am then using reflection to load the assemblies, iterate through the types they contain and identify any that implement my IPlugin interface.

I am checking this with code similar to the following:

foreach(Type t in myTypes )
{
    if( typeof(IPlugin).IsAssignableFrom(t) )
    {
       ...
    }
}

For some reason IsAssignableFrom() keeps returning false when it should be returning true. I have tried replacing the t by explicitly giving it a type that should pass, and it works fine, but for some reason it isn't working with the types that are returned from the loaded assembly. To make things stranger, the code works fine on my co-worker's machine but not on mine.

Does anyone know of anything that might cause this sort of behavior?

Thanks

Answer 1

I am working on a plugin system that loads .dll's contained in a specified folder. I am then using reflection to load the assemblies, iterate through the types they contain and identify any that implement my IPlugin interface.

I am checking this with code similar to the following:

foreach(Type t in myTypes )
{
    if( typeof(IPlugin).IsAssignableFrom(t) )
    {
       ...
    }
}

For some reason IsAssignableFrom() keeps returning false when it should be returning true. I have tried replacing the t by explicitly giving it a type that should pass, and it works fine, but for some reason it isn't working with the types that are returned from the loaded assembly. To make things stranger, the code works fine on my co-worker's machine but not on mine.

Does anyone know of anything that might cause this sort of behavior?

Thanks

Answer 2

I am working on a plugin system that loads .dll's contained in a specified folder. I am then using reflection to load the assemblies, iterate through the types they contain and identify any that implement my IPlugin interface.

I am checking this with code similar to the following:

foreach(Type t in myTypes )
{
    if( typeof(IPlugin).IsAssignableFrom(t) )
    {
       ...
    }
}

For some reason IsAssignableFrom() keeps returning false when it should be returning true. I have tried replacing the t by explicitly giving it a type that should pass, and it works fine, but for some reason it isn't working with the types that are returned from the loaded assembly. To make things stranger, the code works fine on my co-worker's machine but not on mine.

Does anyone know of anything that might cause this sort of behavior?

Thanks

Answer 3

I am working on a plugin system that loads .dll's contained in a specified folder. I am then using reflection to load the assemblies, iterate through the types they contain and identify any that implement my IPlugin interface.

I am checking this with code similar to the following:

foreach(Type t in myTypes )
{
    if( typeof(IPlugin).IsAssignableFrom(t) )
    {
       ...
    }
}

For some reason IsAssignableFrom() keeps returning false when it should be returning true. I have tried replacing the t by explicitly giving it a type that should pass, and it works fine, but for some reason it isn't working with the types that are returned from the loaded assembly. To make things stranger, the code works fine on my co-worker's machine but not on mine.

Does anyone know of anything that might cause this sort of behavior?

Thanks

Answer 4

I am working on a plugin system that loads .dll's contained in a specified folder. I am then using reflection to load the assemblies, iterate through the types they contain and identify any that implement my IPlugin interface.

I am checking this with code similar to the following:

foreach(Type t in myTypes )
{
    if( typeof(IPlugin).IsAssignableFrom(t) )
    {
       ...
    }
}

For some reason IsAssignableFrom() keeps returning false when it should be returning true. I have tried replacing the t by explicitly giving it a type that should pass, and it works fine, but for some reason it isn't working with the types that are returned from the loaded assembly. To make things stranger, the code works fine on my co-worker's machine but not on mine.

Does anyone know of anything that might cause this sort of behavior?

Thanks

Answer 5

I am working on a plugin system that loads .dll's contained in a specified folder. I am then using reflection to load the assemblies, iterate through the types they contain and identify any that implement my IPlugin interface.

I am checking this with code similar to the following:

foreach(Type t in myTypes )
{
    if( typeof(IPlugin).IsAssignableFrom(t) )
    {
       ...
    }
}

For some reason IsAssignableFrom() keeps returning false when it should be returning true. I have tried replacing the t by explicitly giving it a type that should pass, and it works fine, but for some reason it isn't working with the types that are returned from the loaded assembly. To make things stranger, the code works fine on my co-worker's machine but not on mine.

Does anyone know of anything that might cause this sort of behavior?

Thanks

Answer 6

I am working on a plugin system that loads .dll's contained in a specified folder. I am then using reflection to load the assemblies, iterate through the types they contain and identify any that implement my IPlugin interface.

I am checking this with code similar to the following:

foreach(Type t in myTypes )
{
    if( typeof(IPlugin).IsAssignableFrom(t) )
    {
       ...
    }
}

For some reason IsAssignableFrom() keeps returning false when it should be returning true. I have tried replacing the t by explicitly giving it a type that should pass, and it works fine, but for some reason it isn't working with the types that are returned from the loaded assembly. To make things stranger, the code works fine on my co-worker's machine but not on mine.

Does anyone know of anything that might cause this sort of behavior?

Thanks

Answer 7

I had a similar issue which was caused due to dependency injection into plugins. Assume that assembly contains a definition of MyConcreteClass which implements ISomeInterface. MyConcreteClass constructor requires the dependencies I added to the serviceProvider. I am trying to instantiate the object using

 using Microsoft.Extensions.DependencyInjection;

 private IEnumerable<ISomeInterface> CreatePlugins(Assembly assembly)
 {
        ServiceCollection serviceCollestion = new ServiceCollection();
        serviceCollestion.AddSingleton(dependency1);
        serviceCollestion.AddSingleton(dependency2);
        serviceCollestion.AddSingleton(dependency3);
        var serviceProvider = serviceCollestion.BuildServiceProvider();

        foreach (Type type in assembly.GetTypes())
        {
            if (typeof(My.Namespace.ISomeInterface).IsAssignableFrom(type))
            {
                ISomeInterface result = ActivatorUtilities.CreateInstance(serviceProvider, type) as ISomeInterface;
            }
        }
 }

I got the exception:

Unable to resolve service for type 'My.Namespace.ISomeInterface' while attempting to activate 'Another.Namespace.MyConcreteClass'. at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.ConstructorMatcher.CreateInstance(IServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.CreateInstance(IServiceProvider provider, Type instanceType, Object[] parameters)

I then found out that the process which called ActivatorUtilities.CreateInstance was already referencing a dependency of MyConcreteClass and that's why the instantiation failed. In order resolve this I followed the advice from the link below and cleared the folder of Another.Namespace from any assembly referenced by my process prior to loading it.

.NET: Unable to cast object to interface it implements

Answer 8

I am working on a plugin system that loads .dll's contained in a specified folder. I am then using reflection to load the assemblies, iterate through the types they contain and identify any that implement my IPlugin interface.

I am checking this with code similar to the following:

foreach(Type t in myTypes )
{
    if( typeof(IPlugin).IsAssignableFrom(t) )
    {
       ...
    }
}

For some reason IsAssignableFrom() keeps returning false when it should be returning true. I have tried replacing the t by explicitly giving it a type that should pass, and it works fine, but for some reason it isn't working with the types that are returned from the loaded assembly. To make things stranger, the code works fine on my co-worker's machine but not on mine.

Does anyone know of anything that might cause this sort of behavior?

Thanks