gistfile1.cs

Use:

var floatElement = new MVFloatElement(null, null, 0.5);
floatElement.OnValueChange += delegate(fe) {
  //do something with fe.Value, or floatElement.Value
};

public class MVFloatElement : Element
{
    public bool ShowCaption;
    public float Value;
    public float MinValue, MaxValue;
    static NSString skey = new NSString("MVFloatElement");
    UIImage Left, Right;
    UISlider slider;

    //ADDED THIS
    public Action<MVFloatElement> OnValueChange;

    public MVFloatElement(UIImage left, UIImage right, float value)
        : base(null)
    {
        Left = left;
        Right = right;
        MinValue = 0;
        MaxValue = 1;
        Value = value;
    }

    protected override NSString CellKey
    {
        get
        {
            return skey;
        }
    }
    public override UITableViewCell GetCell(UITableView tv)
    {
        var cell = tv.DequeueReusableCell(CellKey);
        if (cell == null)
        {
            cell = new UITableViewCell(UITableViewCellStyle.Default, CellKey);
            cell.SelectionStyle = UITableViewCellSelectionStyle.None;
        }
        else
            RemoveTag(cell, 1);

        SizeF captionSize = new SizeF(0, 0);
        if (Caption != null && ShowCaption)
        {
            cell.TextLabel.Text = Caption;
            captionSize = cell.TextLabel.StringSize(Caption, UIFont.FromName(cell.TextLabel.Font.Name, UIFont.LabelFontSize));
            captionSize.Width += 10; // Spacing
        }

        if (slider == null)
        {
            slider = new UISlider(new RectangleF(10f + captionSize.Width, 12f, 280f - captionSize.Width, 7f))
            {
                BackgroundColor = UIColor.Clear,
                MinValue = this.MinValue,
                MaxValue = this.MaxValue,
                Continuous = true,
                Value = this.Value,
                Tag = 1
            };
            slider.ValueChanged += delegate
            {
                Value = slider.Value;
                //CHANGE HERE
                if (OnValueChange != null) OnValueChange(this);
            };
        }

        cell.ContentView.AddSubview(slider);
        return cell;
    }

    public override string Summary()
    {
        return Value.ToString();
    }

    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            if (slider != null)
            {
                slider.Dispose();
                slider = null;
            }
        }
    }
}