C# reflection example - best practice

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Hello,

Wonder if anyone can advice on best practice using a reflection.
The case I got is as follows:
I got a dll file with multiple classes. Some of those classes implement a particular interface "GetStream". This interface has a property called "Name".
Now - I need to load that dll file and invoke a method of a class implementing "GetStream", where property Name = "SomeName".
Any advice on how to do that without initializing all the classes and checking instances?

I have written the following code, but it fails somewhy:

C#

// load the dll file
Assembly typeLibrary = Assembly.LoadFile(Directory.GetCurrentDirectory() + fileLoc);
string streamName = "SomeName";
foreach (Type t in typeLibrary.GetTypes())
{
   if (t.GetInterfaces().Contains(typeof(GetStream)) && t.Name.Equals(streamName))
   {
      // I never actually get here even, because t.GetInterfaces never contains "GetStream" for some reasons.
      // checking this with a debugger shows exact same type Name and FullName.. I must be missing something here...
   }
}

Any ideas of what that might be, that I am missing ?

By the way - I would prefer avoiding to hardcode the interface name into string like this:

C#

t.GetInterface("GetStream") != null

Event hough it works this does not look like a clean approach and might cause runtime errors if the interface name is changed (there would be no build errors).

Posted 31-Jan-16 23:38pm

MK-Gii

Updated 31-Jan-16 23:55pm

v3

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F-ES Sitecore 1-Feb-16 5:45am

You can use "as" to cast to the interface and if it doesn't support the interface it'll return null.

GetStream gs = myObject as GetStream; // gs will be null if it doesn't support GetStream

Sascha Lefèvre 1-Feb-16 5:56am

You don't have a 'myObject' here, just Types.

MK-Gii 1-Feb-16 5:58am

In this case I would have to create instance for each object in the assembly and then try to cast it. I got like 2000 classes here so creating instance for all classes and casting it would not be efficient.

dan!sh 1-Feb-16 6:01am

[Sascha's correction invalidPoint]Is name static? [/Sascha's correction] If not, how will you check value without an object?

Sascha Lefèvre 1-Feb-16 6:07am

Name can't be static, it's part of an interface.

dan!sh 1-Feb-16 6:07am

Oops. My bad.

Kornfeld Eliyahu Peter 1-Feb-16 6:02am

You are writing both DLLs?

dan!sh 1-Feb-16 6:07am

Also, even if you initialize the object, the property will not have the value you are looking for unless it is the default value specified in DLL loaded.

MK-Gii 1-Feb-16 6:15am

The property Name is returning the name of the class. That's why I can acess propertie - it's only a getter.

dan!sh 1-Feb-16 6:18am

So in that case you need object of class "SomeName". That's it. Right? Once you have it, you can make use of FindInterfaces method and check if the class implements the interface or not.

MK-Gii 1-Feb-16 6:19am

Yes.

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Sascha Lefèvre · Accepted Answer · 2016-02-01T00:05:00

If you remove the && t.Name.Equals(streamName) -part your code will enter the if-block provided that there actually is a Type that implements that interface.

But there's a conceptual problem here: You're dealing with Types only here. There are no instances of any Types and so there can't be any values of properties that are part of an interface (because those can't be static).

Theoretically you would have to create instances of all those Types which implement that interface in order to check the value of that property. But it smells more like you need to re-work your idea here. If you elaborate on why you think you need to do this, we might have an idea how it could be done (differently, probably).

Edit: Btw: t.Name isn't the value of the Name-property. It's the name of the Type. If there wasn't the coincidence that Type has a property 'Name' your code wouldn't compile.