Monotouch.Dialog StyledStringElement delegate always fires for the last element added

Question

given the following code, I am having an issue when clicking on each element. If we assume I have 5 exercises and therefore create 5 elements in the foreach() loop, when the table is rendered and I click on any element, the delegate always gets the exercise of the 5th (last) element.

The elements are displayed properly, each showing the associated exercise's name. It is just the delegate that does not work as expected.

If I do not use a foreach loop and hardcode each element instead it works as expected. However if I cannot dynamically populate the dialogViewController and use the element tapped event for each one, is not good.

private void CreateExerciseTable()
{
Section section = new Section();

foreach (var exercise in exercises)
{
    var element = new StyledStringElement(exercise.ExerciseName, 
        delegate { AddExercise(exercise); }) 
        {
            Font = Fonts.H3,
            TextColor = UIColor.White,
            BackgroundColor = RGBColors.LightBlue,
            Accessory = UITableViewCellAccessory.DisclosureIndicator
        };

    section.Elements.Add(element);
}

var root = new RootElement("Selection") {
    section
};

 var dv = new DialogViewController(root, true);
dv.Style = UITableViewStyle.Plain;

//Remove the extra blank table lines from the bottom of the table.
UIView footer = new UIView(new System.Drawing.RectangleF(0,0,0,0));
dv.TableView.TableFooterView = footer;

dv.TableView.SeparatorColor = UIColor.White;
dv.TableView.BackgroundColor = UIColor.White;
tableFitnessExercises.AddSubview(dv.View);      
}

private void AddExercise(FitnessExercise exercise)
{
NavigationManager.FitnessRoutine.Add(exercise);
PerformSegue(UIIdentifierConstants.SegAddExerciseToFitnessRoutine, this);
}

Answer 1

This is a classic closure bug!

The problem is that you are accessing the loop reference.

Try:

foreach (var exercise in exercises)
{
    var localRef = exercise;
    var element = new StyledStringElement(exercise.ExerciseName, 
        delegate { AddExercise(localRef); }) 
        {
            Font = Fonts.H3,
            TextColor = UIColor.White,
            BackgroundColor = RGBColors.LightBlue,
            Accessory = UITableViewCellAccessory.DisclosureIndicator
        };

    section.Elements.Add(element);
}

For more on this see http://blogs.msdn.com/b/ericlippert/archive/2009/11/12/closing-over-the-loop-variable-considered-harmful.aspx