how to correct the parameter count mismatch

Question

How can I correct this error I'm having

TargetParameterCountException was unhandled by user code. Parameter count mismatch.

This is my code where it's happening

public static void InvokeMethod(string className, string methodName, string fileName)
{
    var t = Type.GetType(className);
    using (StreamReader f = new StreamReader("params.txt"))
    {
        t.GetMethod(methodName).Invoke(t.GetConstructor(Type.EmptyTypes).Invoke(new object[] { }), new object[] { f.ReadLine() });
    }
}

This is the whole code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.IO;

class MyClass
{
    private int i;
    public double d;
    private string s;
    public bool b;
    public MyClass()
    {
        i = 1;
        d = 0.1;
        s = "1";
        b = true;
    }
    public void Method0()
    {
        Console.WriteLine("Method with no arguments, no return value.");
    }
    private int Method1(int arg0)
    {
        Console.WriteLine("The method returns int, int gets.");
        return arg0;
    }
    private double Method2(int arg0, double arg1)
    {
        Console.WriteLine("Method returns a double, taking int and double.");
        return arg1 * arg0;
    }
    public bool Method3(string arg0)
    {
        Console.WriteLine("Method returns a bool, accepts string");
        return arg0.Length>10;
    }
    public bool Method3(string arg0,string arg1)
    {
        Console.WriteLine("The method takes two arguments string.");
        return arg0 == arg1;
    }
    public static char Method4(string arg0)
    {
        Console.WriteLine("Method returns a char, accepts string. .");
        Console.WriteLine(arg0);
        return arg0[1];
    }
    public void Method5(int arg0, double arg1)
    {
        Console.WriteLine("arg1 = {0} arg2 = {1}.",arg0,arg1);
    }
}

class MyTestClass
{
    public static string[] GetMethodsWithStrParams(string className)
    {
        var t = Type.GetType(className);
        List<string> res = new List<string>();
        foreach (var method in t.GetMethods())
        {
            foreach (var param in method.GetParameters())
            {
                if (param.ParameterType == typeof(string))
                {
                    res.Add(method.Name);
                    break;
                }
            }
        }
        return res.ToArray();
    }
    public static void InvokeMethod(string className, string methodName, string fileName)
    {
        var t = Type.GetType(className);
        using (StreamReader f = new StreamReader("params.txt"))
        {
            t.GetMethod(methodName).Invoke(t.GetConstructor(Type.EmptyTypes).Invoke(new object[] { }),
                                           new object[] { f.ReadLine() });
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        string name = "MyClass";

        foreach (var x in MyTestClass.GetMethodsWithStrParams(name))
        {
            Console.WriteLine(x);
        }

        MyTestClass.InvokeMethod("MyClass", "Method5", "params.txt");

        Console.ReadKey(true);
    }
}

Answer 1

Your InvokeMethod implementation always calls t.GetMethod(methodName).Invoke with two arguments, the first being the target instance on which the method is called, and second being the array of method arguments, which contains only one string (f.ReadLine()).

Then you use InvokeMethod to call MyClass.Method5 which takes two arguments, an int and a double. This obviously can't work, as myClass.Method5("some string") is syntactically incorrect, and this is what effectively happens. You can't expect that a string is a valid argument list for all MyClass methods, can you?

That is the cause of the error, but only you can decide how to fix it, as we don't know the greater context. You have to provide the correct number of parameters depending on the actual method being called.

Possible path to solution:

• what are the arguments I want to provide to Method5?
• where do I get them from?
• how do I move them from wherever they are to the array I give to Invoke?

This should get you started, but no one can tell you exactly as you have only described the error, but not the real problem you are trying to solve with your code.

Answer 2

The error doesn't need any correction, it is correct. ;)

You are trying to call a method that takes two parameters with an array of parameters that only contains one item.

A parameter array that would work for that specific method would for example be:

new object[] { 0, 1.5 }

If you want your InvokeMethod method to work with methods that take different number of parameters with different types, you have to create different parameter arrays for each combination.