Storing a method as a member variable of a class

问题:

I have this as one of my members of the class 'KeyEvent':

private delegate void eventmethod();

And the constructor:

public KeyEvent(eventmethod D) 
{
    D();
}

What I want to do is instead of calling D() there, I want to store that method (D) as a member variable of KeyEvent, so something like:

stored_method = D();

And then later in another method of KeyEvent, do something like:

stored_method();

How can I do this?

回答1:

You pretty much have the code already. Just create a member field of the right delegate type and save the parameter to it just like you would with any other data type.

private eventmethod MySavedEvent;

public void KeyEvent(eventmethod D) {
    // Save the delegate
    MySavedEvent = D;
}

public void CallSavedEvent() {
    if (MySavedEvent != null) {
        MySavedEvent();
    }
}

回答2:

You could do something like:

private Action CallBackFunction {get; set;}

public KeyEvent(Action callback) {
   CallBackFunction = callback;
}

Which can be instantiated by:

new KeyEvent(MyFunction);

Where MyFunction is the name of some function in that class

The KeyEvent class can then invoke that function with:

CallBackFunction();

The Action class also allows strongly typed parameters to be passed in and the Func class can be used for methods that return a result.

回答3:

the thing that you want is called "first class function" http://en.wikipedia.org/wiki/First-class_function

C#, since version 3, supports anonymous functions and lambda expressions.

So you can use Func<A,R> which represents a function taking an argument of type A and returning a value of type R

from wiki

static Func<double, double> MakeDerivative(Func<double, double> f, double deltaX)
  {
    return (x) => (f(x + deltaX) - f(x - deltaX)) / (2 * deltaX);
  }

回答4:

public class KeyEvent
{
  private eventmethod hurr;
  public KeyEvent(eventmethod D)
  {
    hurr = D;
  }
  public void SomeOtherMethod()
  {
    hurr();
  }
}

Couple things... PascalCase types/delegates/etc (EventMethod) and camelCase arguments (d, dIsMyMethod). And reuse what the framework gives you: private Action hurr;