C# 在运行时确定泛型类型参数

Question

If a named class exists, I want to pass that class as the type parameter to a generic method. Otherwise I want to pass a different type. I cannot figure out how to pass the type parameter to the generic method.

// Does this type exist?
Type objType = Type.GetType(typeof(ModelFactory).Name + "." + content_type + "Model");

// if not, use this type instead
if (objType == null)
{
    objType = typeof(GenericModel);
}

// what to pass as the generic type argument?
var other = query.Find<objType>().ContinueWith((t) =>

Is it possible? What do I pass to Find in the last line instead of objType?

Thanks & regards,

-John

Answer 1

You must use the Reflection API. Once you get the argument type for your Find method, you need to get a MethodInfo from the Find method and pass an instance of the class that defines that method and the necessary parameters for the method, an example:

public class GenericModel {}

// This class simulates the class that contains the generic Find method
public class Query {
    public void Find<T>() {
        Console.WriteLine("Invoking Find method...");
    }
}

class Program {
    static async Task Main(string[] args) {
        var theType = typeof(GenericModel);

        // Obtaining a MethodInfo from the Find method
        var method = typeof(Query).GetMethod(nameof(Query.Find)).MakeGenericMethod(theType);
        var instanceOfQuery = Activator.CreateInstance(typeof(Query));
        var response = method.Invoke(instanceOfQuery, null); // Cast the method to your return type of find.

        Console.ReadLine();
    }
}