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c#genericsreflectioninvokeparameters
Stevie
Stevie

Reputation: 196

Invoking Generic method with params parameter through reflection

I am trying to invoke a generic methods that accepts a single params parameter through reflection. When I picked it to be non generic passing an object[] item seemed to be sufficient but when I reqired to call a generic method it does not work anymore.

var type = typeof (ClassWithGenericMethod);
var method = type.GetMethod("GenericMethod", BindingFlags.Instance | BindingFlags.Public);
var genericMethod = method.MakeGenericMethod(typeof(object));
var result = (bool)genericMethod.Invoke(new ClassWithGenericMethod(), new object[]{"param"});
Assert.IsTrue(result);

The called class:

public class ClassWithGenericMethod
{
    public bool GenericMethod<T>(params string[] input)
    {
        return input.Length == 1;
    }
}

The code fails before the assert with the following exception:

Object of type 'System.String' cannot be converted to type 'System.String[]'.

Upvotes: 2

Views: 2065

Answers (2)

Grax32
Grax32

Reputation: 4069

When using reflection to call a method that has a params keyword specified, you should just ignore the params keyword. You will need to specify an array of the appropriate type and pass that as the argument.

In your case, instead of passing a single parameter of "param", you need to pass an array of string containing a single item.

The params keyword actually affects how the method caller is compiled. When the compiler sees that the called method specifies "params", it builds the appropriate type of array and passes it. The compiler "magically" turns the following

string result = string.Concat("A","B","C","D");

into basically a compiled version of the following

string[] x = {"A", "B", "C", "D"};
string result = string.Concat(x);

Upvotes: 0

Cheng Chen
Cheng Chen

Reputation: 43531

Try repleace new object[]{"param"} with new object[] { new[] { "param" } }.

Here new object[] is the array of parameters, and the first parameter should be a string[], but in your code, you use a string, hence the exception.

Upvotes: 5

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