如何将该事件展开为可观察的序列？

Question

Well, just when I think I've got a handle on things, I get thrown another curve.

I'm trying to create an observable sequence instead of doing this:

((Outlook.MAPIFolderEvents_12_Event)calendarFolder).BeforeItemMove += 
   Calendar_BeforeItemMove;

private void Calendar_BeforeItemMove(
    object item, 
    Outlook.MAPIFolder destFolder, 
    ref bool cancel){ /*...*/ }

I'm trying to use the Observable.FromEventPattern<TDelegate, TEventArgs> (Func<EventHandler<TEventArgs>, TDelegate>, Action<TDelegate>, Action<TDelegate>) method, but because of the required parameters I'm meeting with little success. The closest I have been able to come is:

var itemBeforeMovedObservable = Observable
    .FromEvent<Outlook.MAPIFolderEvents_12_BeforeItemMoveEventHandler, object>(handler =>
    {
       Outlook.MAPIFolderEvents_12_BeforeItemMoveEventHandler bimEventHandler =
       (obj, f, ref cx) =>  // <-- Cannot resolve symbol 'cx'; Identifier expected
       {
          handler(obj); // <-- shouldn't this have the other parameters as well?
       };
       return bimEventHandler;
    },
    h => ((Outlook.MAPIFolderEvents_12_Event)calendarFolder).BeforeItemMove += h,
    h => ((Outlook.MAPIFolderEvents_12_Event)calendarFolder).BeforeItemMove -= h);

Thanks in advance for any guidance.

Answer 1

I don't really have access to a way to test this but I would say you would probably be best off wrapping it up into an operator:

//Because that naming is ridiculous
using ItemMoveEventHandler = Outlook.MAPIFolderEvents_12_BeforeItemMoveEventHandler; 
using ItemMoveEvent = Outlook.MAPIFolderEvents_12_Event;

//Used to wrap multiple arguments into a single object
public class MyMoveEventArgs {
  public MyMoveEventArgs(Object item, MAPIFolder folder) {
    this.Item = item;
    this.Folder = folder;
  }

  public Object Item {get; private set;}
  public MAPIFolder Folder {get; private set;}
}

//Create an extension method
public static IObservable<MyMoveEventArgs> BeforeMoveObservable(
  this ItemMoveEvent folder, 
  Func<object, MAPIFolder, bool> shouldCancel) {

    return Observable.FromEvent<ItemMoveEventHandler, 
                              MoveEventArgs>
                    //Use the conversion overload
                    (emit => new ItemMoveEventHandler(
                          //The compiler seems to complain about cancel
                          //being implicit, so explicitly declare your params
                          (object item, MAPIFolder f, out bool cancel) => 
                          {
                            //cancel needs to be set somewhere in the body
                            if (!(cancel = shouldCancel(item, f)) {
                             emit(new MyMoveEventArgs(item, f));
                            }
                          }
                    },
                    h => folder.BeforeItemMove += h,
                    h => folder.BeforeItemMove -= h);

}

Then you should be able to use it like so (untested):

calendarFolder.BeforeMoveObservable((obj, folder => /*Return if the event should be cancelled or not*/)
.Subscribe(x => /*Only reach here if the move was successful*/);