How to make work UIDocumentInteractionController in MonoTouch

Question

I am trying to open a *.epub file throught my application and I don't quite understand how to make it with the UIDocumentInteractionController class. I have seen the official IOS documentation and examples and some of the examples over the net but I don't understand how that class works. This is how I do it, what I achieve and what I dont understand:

I have a UIView with a UIButton:

using MonoTouch.UIKit;
using MonoTouch.Foundation;
using System.Drawing;

public class MyView : UIViewController
{
    UIButton myBtn;

    public MyView() :base()
    {
        View.Frame = new RectangleF(0,0,1024,768);

        var myRect = new RectangleF(300,300,100,50);

        myBtn = UIButton.FromType(UIButtonType.RoundedRect);
        myBtn.Frame = myRect;
        myBtn.TouchUpInside += delegate
        {
            var dic = UIDocumentInteractionController.FromUrl(new NSUrl("http://192.168.50.50:2020/myfile.epub"));
            var dicDel = new UIDocumentInteractionControllerDelegate();
            dic.Delegate = dicDel;

            InvokeOnMainThread(delegate
            {
                var result = dic.PresentOpenInMenu(myRect, View, true);
                //If I do this -> NullReferenceException because delegate is null (something about autorelease?? Don't know)
                if(!result) dic.Delegate.DidDismissOpenInMenu(dic);
            });


        }
    }
}

The weirdest thing is if I debug and inspect "dic" (without the delegate) before calling the PresentOpenInMenu() method it shows the menu (returning true) but just after doing it the app blows up on Main.cs because the autorelease thing I dont understand.

I am a little lost. Can someone help me understand this class and how can I make it work correctly? Thanks in advance.

EDIT: By the way, I used a *.txt file too with same results.

Answer 1

It looks like a MonoTouch bug. Setting the UIDocumentInteractionController.Delegate (or WeakDelegate property and then querying its value returns null (which will fail later on).

I'll look into this bug and update this answer if I can provide a workaround (until the bug is properly fixed in a future release of MonoTouch).

UPDATE: UIDocumentInteractionController already creates it's own internal UIDocumentInteractionControllerDelegate so you do not need to create one. The Delegate methods, like DidDismissOpenInMenu are available as events on UIDocumentInteractionController itself.

Remove your own Delegate (creation and set) and use the events and you should be fine.

UPDATE #2: The Delegate property returns null since the default UIDocumentInteractionControllerDelegate is not usable as is. It is meant to be inherited from and customized to do what you want to (and the unusable default one is not registred properly to be used). E.g.

class MyDocumentInteractionControllerDelegate : UIDocumentInteractionControllerDelegate { }

and

var dicDel = new MyDocumentInteractionControllerDelegate ();

would work, as in no NullReferenceException, but of course DidDismissOpenInMenu won't be doing anything interesting.