Pass Method as Parameter using C#

Question

I have several methods all with the same signature (parameters and return values) but different names and the internals of the methods are different. I want to pass the name of the method to run to another method that will invoke the passed in method.

public int Method1(string)
{
    ... do something
    return myInt;
}

public int Method2(string)
{
    ... do something different
    return myInt;
}

public bool RunTheMethod([Method Name passed in here] myMethodName)
{
    ... do stuff
    int i = myMethodName("My String");
    ... do more stuff
    return true;
}

public bool Test()
{
    return RunTheMethod(Method1);
}

This code does not work but this is what I am trying to do. What I don't understand is how to write the RunTheMethod code since I need to define the parameter.

Answer 1

You can also try Action Delegate!

 public static int Method1(string mystring)
 {
      return 1;
 }

 public static int Method2(string mystring)
 {
     return 2;
 }

 public bool RunTheMethod(Action myMethodName)
 {
      myMethodName();
      return true;
 }

And then call your method using

RunTheMethod(() => Method1("MyString1"));

Or

public static object InvokeMethod(Delegate method, params object[] args)
{
     return method.DynamicInvoke(args);
}

Then simply call method

Console.WriteLine(InvokeMethod(new Func<string,int>(Method1), "MyString1"));

Console.WriteLine(InvokeMethod(new Func<string, int>(Method2), "MyString2"));

Answer 2

public static T Runner<T>(Func<T> funcToRun)
{
    //Do stuff before running function as normal
    return funcToRun();
}

Usage:

var ReturnValue = Runner(() => GetUser(99));

Answer 3

If you want the ability to change which method is called at run time I would recommend using a delegate: http://www.codeproject.com/KB/cs/delegates_step1.aspx

It will allow you to create an object to store the method to call and you can pass that to your other methods when it's needed.

Answer 4

While the accepted answer is absolutely correct, I would like to provide an additional method.

I ended up here after doing my own searching for a solution to a similar question. I am building a plugin driven framework, and as part of it I wanted people to be able to add menu items to the applications menu to a generic list without exposing an actual Menu object because the framework may deploy on other platforms that don't have Menu UI objects. Adding general info about the menu is easy enough, but allowing the plugin developer enough liberty to create the callback for when the menu is clicked was proving to be a pain. Until it dawned on me that I was trying to re-invent the wheel and normal menus call and trigger the callback from events!

So the solution, as simple as it sounds once you realize it, eluded me until now.

Just create separate classes for each of your current methods, inherited from a base if you must, and just add an event handler to each.

Answer 5

You need to use a delegate. In this case all your methods take a string parameter and return an int - this is most simply represented by the Func<string, int> delegate¹. So your code can become correct with as simple a change as this:

public bool RunTheMethod(Func<string, int> myMethodName)
{
    // ... do stuff
    int i = myMethodName("My String");
    // ... do more stuff
    return true;
}

Delegates have a lot more power than this, admittedly. For example, with C# you can create a delegate from a lambda expression, so you could invoke your method this way:

RunTheMethod(x => x.Length);

That will create an anonymous function like this:

// The <> in the name make it "unspeakable" - you can't refer to this method directly
// in your own code.
private static int <>_HiddenMethod_<>(string x)
{
    return x.Length;
}

and then pass that delegate to the RunTheMethod method.

You can use delegates for event subscriptions, asynchronous execution, callbacks - all kinds of things. It's well worth reading up on them, particularly if you want to use LINQ. I have an article which is mostly about the differences between delegates and events, but you may find it useful anyway.

---

¹ This is just based on the generic Func<T, TResult> delegate type in the framework; you could easily declare your own:

public delegate int MyDelegateType(string value)

and then make the parameter be of type MyDelegateType instead.

Answer 6

Here is an example Which can help you better to understand how to pass a function as a parameter.

Suppose you have Parent page and you want to open a child popup window. In the parent page there is a textbox that should be filled basing on child popup textbox.

Here you need to create a delegate.

Parent.cs // declaration of delegates public delegate void FillName(String FirstName);

Now create a function which will fill your textbox and function should map delegates

//parameters
public void Getname(String ThisName)
{
     txtname.Text=ThisName;
}

Now on button click you need to open a Child popup window.

  private void button1_Click(object sender, RoutedEventArgs e)
  {
        ChildPopUp p = new ChildPopUp (Getname) //pass function name in its constructor

         p.Show();

    }

IN ChildPopUp constructor you need to create parameter of 'delegate type' of parent //page

ChildPopUp.cs

    public  Parent.FillName obj;
    public PopUp(Parent.FillName objTMP)//parameter as deligate type
    {
        obj = objTMP;
        InitializeComponent();
    }



   private void OKButton_Click(object sender, RoutedEventArgs e)
    {


        obj(txtFirstName.Text); 
        // Getname() function will call automatically here
        this.DialogResult = true;
    }