passing unknown class as parameter and trying to run function on it

Question

Using C#, lets say I have these classes:

classZero
classOne
classTwo

class classZero and classOne have a public function named "Hello()".

how can i creat a new function (in any class) that takes a unknown class as a paramenter and then run the function "Hello" on this unknown class, if it exists?

in sebdo code this would look something like this:

function runHelloIfPossible(anyclass aclass):
   if aclass contains function Hello:
      aclass.Hello()

if in my case the anyclass argument where any of classZero or classOne the function Hello would run.

You can also implemt an interface, check if the object has the interface, then call it — devzero, Feb 17 '20 at 10:57
@HimBromBeere does the duplicate really fit the OP requirements? — Pavel Anikhouski, Feb 17 '20 at 10:58
@PavelAnikhouski Why do you think it does not? From my understanding OP has a function-name that he wants to call. — MakePeaceGreatAgain, Feb 17 '20 at 10:59
I agree with @PavelAnikhouski, there are other ways to do this and this is not a direct duplicate. — jason.kaisersmith, Feb 17 '20 at 11:00
Use interface IHello on classZero and classOne -> if (aclass is IHello ih) {ih.Hello()} — Ive, Feb 17 '20 at 11:00
This question is about using a base class or interface for 3 classes on OP question, or about pattern matching with `switch` expression, it isn't about reflection, IMO — Pavel Anikhouski, Feb 17 '20 at 11:00
@PavelAnikhouski okay, I see your point. However as of OPs current code there is no interface existing. Creating one would be part of the solution, though. — MakePeaceGreatAgain, Feb 17 '20 at 11:01
Is there any base-class or interface all your three classes implement? Can you create one if not? — MakePeaceGreatAgain, Feb 17 '20 at 11:01
Base class or interface isn't necessary, OP can use an `object` class. Base class or interface will simplify the solution — Pavel Anikhouski, Feb 17 '20 at 11:04
@PavelAnikhouski `object` has no method called `Hello`. How should that work? — MakePeaceGreatAgain, Feb 17 '20 at 11:20
There are two reopen votes already, one more is needed. Then the possible solutions can be added as an answers — Pavel Anikhouski, Feb 17 '20 at 11:20
@HimBromBeere using pattern matching with `switch` or `is` operators. I've almost written an answer before you closed the question:) — Pavel Anikhouski, Feb 17 '20 at 11:22
@HimBromBeere not to be rude but I rly don't se how this question is a dublicate of the one sugested. I need to pass a class as an argument and then run a function on that class (if the function exists). I can't se how your proposed dublicated answere explains how to do this...? to clarify, the class passed can be any class and therefore don't need to have the function — user10483669, Feb 17 '20 at 11:46

score 1 · Answer 1 · answered Feb 17 '20 at 11:28

1

public interface IHello
{
    void Hello();
}

public class Zero: IHello
{
    public void Hello()
    {
    }
//...
}

...

void RunHelloIfPossible(object obj)
{
   if (obj is IHello ih)
   {
      ih.Hello();
   }
}

answered Feb 17 '20 at 11:28

Ive

1,321
2
17
25

Thx @Ive!, sadly I'm not allowed to add an interface, if I where this would be a good answere! :) – user10483669 Feb 17 '20 at 12:13

Pavel Anikhouski · Accepted Answer · 2020-02-21T09:22:50.850

You can use type pattern matching with switch statement for that (it's available from C# 7)

public void RunHelloIfPossible(object anyObject)
{
    switch (anyObject)
    {
        case classZero zero:
            zero.Hello();
            break;
        case classOne one:
            one.Hello();
            break;
    }           
}

Example of the usage

RunHelloIfPossible(new classOne());

If both classes implement the same interface (lets say IHello) or base class, the code above can be simplified to

if (anyObject is IHello hello)
{
    hello.Hello();
}

score 1 · Answer 3 · answered Feb 18 '20 at 07:41

the key word dynamic can be used, please see below codes.

class Program
{
    static void Main(string[] args)
    {
        var class0 = new ClassZero();
        var class1 = new ClassOne();
        var class2 = new ClassTwo();
        var class3 = new ClassWithoutHello();

        class2.DynamicCall(class0);
        class2.DynamicCall(class3);

        Console.ReadLine();
    }
}

public class ClassZero
{
    public void Hello()
    {
        Console.WriteLine("say hello from Class Zero");
    }
}

public class ClassOne
{
    public void Hello()
    {
        Console.WriteLine("say hello from Class One");
    }
}

public class ClassWithoutHello
{

}

public class ClassTwo
{
    public void DynamicCall(dynamic input)
    {
        Console.WriteLine("calling input from Class Two");

        if ((input is ClassZero) || (input is ClassOne))
        {
            input.Hello();
        }
        else
        {
            Console.WriteLine("this type does NOT support hello method");
        }
    }
}

passing unknown class as parameter and trying to run function on it

3 Answers3