CODEWITHSUNDEEP
c#.netparametersdelegatesinvoke
Марк Павлович
Марк Павлович

Reputation: 509

System.Reflection.TargetParameterCountException when Parameter count can be dynamic

All methods in the "ProbabilitiesTheory" class accept dynamic count of parameters - it means that there can be put as many parameters as one wants. But .NET still says "System.Reflection.TargetParameterCountException" when invoking a method, that has "params" keyword in its parameters.

Here's the code:

internal static class ProbabilitiesTheory
{
    static public double GetMediumValue(params double[] integers)
    { }
}
class Program
{
    static void Main(string[] args)
    {
        MethodInfo[] methods = Type.GetType("ConsoleApplication1.ProbabilitiesTheory").GetMethods();

        while (true)
        {
            Console.WriteLine("Write the name of the method\n");
            string NameOfMethod = Console.ReadLine();

            Console.WriteLine("Write the parameters of the method using the following format: 
            parameter1;parameter2;parameter3;parameterN\n");
            string ParametersOfMethod = Console.ReadLine();

            foreach (var i in methods)
            {
                if (i.Name == NameOfMethod)
                {
                    object[] @parameters = (from t in ParametersOfMethod.Split(';') where t != "" select (object)Convert.ToDouble(t)).ToArray();

                    i.Invoke(null, @parameters); // Exception HERE
                }
            }
            Console.WriteLine("______");
        }
    }
}

It is absolutely ok with LINQ expression there, i get what i need to get: object[] containing dynamic amount of double values.

How do i solve this problem?

Upvotes: 0

Views: 1614

Answers (1)

Jonathon Chase
Jonathon Chase

Reputation: 9704

As far as reflection is concerned, a params array is just an array with a fancy syntactical sugar. You could solve the immediate problem for most of your methods by adjusting your code like so:

double[] @parameters = (from t in ParametersOfMethod.Split(';') where t != "" select Convert.ToDouble(t)).ToArray();

i.Invoke(null, new[] { @parameters});

The gist of this is that a params array is just a single parameter at run-time, and the ability to add a variable amount of values to it is just a nicety done by the compiler.

You can confirm this with a snippet like this:

void Main()
{
    var parameterCount = typeof(Test).GetMethod("Foo").GetParameters().Count();
    Console.WriteLine(parameterCount); // Output: 2
}

// Define other methods and classes here
public static class Test 
{
    public static void Foo(double x, params double[] y) 
    {}
}

If you need to invoke a function that uses a params array with user provided values when the params array is not the only parameter, you're going to need to get the method parameter count and work out where the array actually starts, then wrap things accordingly.

Upvotes: 1

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