how do I combine several Action<T> into a single Action<T> in C#?

问题

How do I build an Action action in a loop? to explain (sorry it's so lengthy)

I have the following:

public interface ISomeInterface {
    void MethodOne();
    void MethodTwo(string folder);
}

public class SomeFinder : ISomeInterface 
{ // elided 
} 

and a class which uses the above:

public Map Builder.BuildMap(Action<ISomeInterface> action, 
                            string usedByISomeInterfaceMethods) 
{
    var finder = new SomeFinder();
    action(finder);
}

I can call it with either of these and it works great:

var builder = new Builder();

var map = builder.BuildMap(z => z.MethodOne(), "IAnInterfaceName");
var map2 = builder(z =>
                   {
                     z.MethodOne();
                     z.MethodTwo("relativeFolderName");
                   }, "IAnotherInterfaceName");

How can I build the second implementation programmatically? i.e.,

List<string> folders = new { "folder1", "folder2", "folder3" };
folders.ForEach(folder =>
               {
                 /* do something here to add current folder to an expression
                  so that at the end I end up with a single object that would
                  look like:
                  builder.BuildMap(z => {
                                   z.MethodTwo("folder1");
                                   z.MethodTwo("folder2");
                                   z.MethodTwo("folder3");
                                   }, "IYetAnotherInterfaceName");
                */
                });

I've been thinking I need an

Expression<Action<ISomeInterface>> x 

or something similar, but for the life of me, I'm not seeing how to construct what I want. Any thoughts would be greatly appreciated!

回答1:

It's really easy, because delegates are already multicast:

Action<ISomeInterface> action1 = z => z.MethodOne();
Action<ISomeInterface> action2 = z => z.MethodTwo("relativeFolderName");
builder.BuildMap(action1 + action2, "IAnotherInterfaceName");

Or if you've got a collection of them for some reason:

IEnumerable<Action<ISomeInterface>> actions = GetActions();
Action<ISomeInterface> action = null;
foreach (Action<ISomeInterface> singleAction in actions)
{
    action += singleAction;
}

Or even:

IEnumerable<Action<ISomeInterface>> actions = GetActions();
Action<ISomeInterface> action = (Action<ISomeInterface>)
    Delegate.Combine(actions.ToArray());

来源：https://stackoverflow.com/questions/2559807/how-do-i-combine-several-actiont-into-a-single-actiont-in-c